High back EMF, high pressure subwoofer having small volume cabinet, low frequency cutoff and pressure resistant surround
A subwoofer cabinet having a volume less that 1 ft3 axially aligned openings in opposed cabinet walls; first and second cages mounted on respective ones of the walls in alignment with the openings; a voice coil driven driver including an annular 225 oz. magnet affixed to the first cage; a stationary pole piece extending through the magnet and defining a magnetic gap therebetween; a voice coil mounted on a cylindrical voice coil former positioned within the gap; a cone affixed to one end of the former; a first flexible surround secured to the outer end of the cone and attached at its periphery to the first cage; a flexible spider secured to the former and at its outer periphery to the first cage; a mass driven driver including a 1.7 lb. mass; a second flexible surround secured to the mass and to the second cage; a flexible spider attached to the second cage and to the mass; both surrounds having a uniform thickness of at least 0.1″, an edgeroll having a diameter of at least 1.5″, and capable of standing off internal pressures of 1.5 lbs./in2 to 3 lbs./in2; a drive amplifier capable of delivering 2,700 watts to a nominal 4 ohm resistive load and swinging 104 volts for delivering (+)-v and (−)-v drive signals to the voice coil for driving the voice coil driven driver through a peak-to-peak stroke of about 2.5″ while generating a large back emf sufficient to counter the applied emf and minimize current flow in the voice coil.
The present Application is related to, based on, a continuation-in-part of, and, for all common subject matter contained therein, claims priority from, Applicant's co-pending Provisional Application No. 60/023,784, filed Aug. 12, 1996, entitled “HIGH BACK EMF, HIGH PRESSURE SUBWOOFER HAVING SMALL VOLUME CABINET, LOW FREQUENCY CUTOFF AND PRESSURE RESISTANT SURROUND”.
The present Application is also related to, a continuation-in-part of, and describes and claims improvements on, the invention disclosed and claimed in Applicant's co-pending U.S. patent application Ser. No. 08/582,149, filed Jan. 2, 1996, entitled “HIGH POWER AUDIO SUBWOOFER”, now U.S. Pat. No. 5,748,753 issued May 5, 1998.
BACKGROUND OF THE INVENTION1. Field of the Invention
The present invention relates generally to the field of high fidelity audio reproduction; and, more particularly, concerns subwoofer loudspeaker systems that produce high quality, low distortion and low-frequency sound.
2. Prior Art
In the field of high fidelity sound reproduction, a high quality audio system is normally comprised of: a) a signal source, which is generally music or soundtracks from: i) films; ii) compact disk players; iii) laser disk players, and the like; b) a “preamplifier” which receives signals from the signal source and provides an audio signal to a power amplifier which amplifies the signal; and c), loudspeakers that can reproduce the sound from the signal source. Generally, loudspeakers are single enclosures designed to produce most of the audible frequency range, which is from. 20 Hertz (“Hz”) to 20,000 Hz.
Modern recording technologies have allowed music and film Producers to make recordings having wider dynamic ranges—i.e., higher signal-to-noise ratios—and more extended frequency response. Furthermore, many music and film recordings contain more low frequency information than those of only a few years ago. This is especially true in film soundtracks, where recordings of special effects such as explosions are commonplace.
In response to the increased low frequency sound in recordings, a growing number of audio systems are adding an additional type of loudspeaker to their existing array of loudspeakers. This type of loudspeaker is known as a “subwoofer”. Subwoofers are specialized loudspeakers which reproduce only the lowest frequencies of the audible frequency range—viz., those frequencies ranging from approximately 20 Hz, or lower, to about 80 to 120 Hz. These low frequencies are difficult for many full range loudspeakers to reproduce because the bass drivers for full range loudspeakers must handle a wider frequency range—i.e., their frequency response must extend much higher in the audible frequency range, often to about 2,500 Hz or even higher depending upon the design of the loudspeaker. Adding a subwoofer to an audio system relieves the full range loudspeaker from reproducing the lowest frequencies, thereby improving its performance. In addition, certain standards are being set for the reproduction of film soundtracks at home which require the use of one or more subwoofers. Such standards include THX® (a registered trademark of Lucas Film, Ltd.) certification from Lucas Film and Dolby AC-3 Surround Sound® (a registered trademark of J.C. Penney Company, Inc.) from Dolby Laboratories. Dolby AC-3 Surround Sound® even has an audio channel dedicated to only low frequency information.
Conventional design of a subwoofer involves the placement of one or more large bass drivers into a large cabinet—e.g., typically a cabinet enclosing a volume of space ranging from about 8 cubic feet to about 27 cubic feet. Bass drivers, known as “woofers”, generally include a circular “diaphragm” or “cone” which can be constructed of many different materials including paper, plastic, kevlar, etc. Woofer cones have a certain diameter—viz., the bore of the cone is equal to pi×radius2 (πr2). Prior art subwoofer cones capable of high acoustic output generally have a diameter of at least ten inches, and often greater.
The circumference of the cone is affixed to a “surround” or “suspension”, which is then affixed to the driver's frame. The suspension enables the cone to move in and out of the driver frame at a particular frequency and returns it to a null position when no sound is produced. The peak-to-peak distance traveled by the cone is known as the “stroke” of the driver—sometimes referred to as the “excursion” of the driver. Generally, the drivers installed in prior art subwoofers have a peak-to-peak stroke or excursion of between 0.4″ and 0.6″. Prior art suspensions are constructed of flexible, compliant materials such as relatively thin rubber, impregnated cloth, expanded synthetic cellular foam such, for example, as expanded cellular polyethylene (“PE”) surround foam, or similar materials which are compressed to a thickness of about 0.02″ and which are not self-supporting, which have historically produced very little resistance to peak-to-peak cone movement, and which are capable of standing off box pressures of only on the order of nominally about 0.1 lbs/in2 and, at best, only about 0.15 lbs/in2.
Movement of the cone about the suspension causes air to be moved, which is what produces the sound heard and, in the case of bass, felt by the listener. The amount of air that can be moved by a driver is directly related to the bore and stroke of the subwoofer cone. Thus, to increase the amount of air that a subwoofer can move, the bore, the stroke, and/or both the bore and stroke, can be increased. However, and as will be discussed below, simply increasing the bore and/or the stroke has disadvantages.
At the center of the cone, the driver is affixed to the “motor” of the cone which is comprised generally of a single electrical conductor placed within a magnetic field. In the prior art, the electrical conductor is a single electrical wire wrapped around a cylinder. This arrangement is know as the “voice coil” of the driver. The voice coil is wrapped around a voice coil former which is, in turn, affixed to the cone of the driver and placed in proximity to a magnet. When current is run through the voice coil, magnetic fields are created around the voice coil. These voice coil magnetic fields interact with the magnetic fields of the magnet, which causes the voice coil former to move. The voice coil former's movement causes the movement of the cone. Cone movement, as discussed above, causes movement of air which produces sound. Producing sound at higher volumes requires greater cone movements. Greater cone movements are produced when the voice coil and the driver's magnet have greater magnetic field interactions; and, this increased magnetic field interaction is produced when the voice coil has more current running through it.
To reproduce low frequencies at high volume levels, a subwoofer must be capable of moving large quantities of air. Typical prior art subwoofers for use in the home can move approximately one-hundred thirty cubic inches of air. For louder audio volumes, it is desirable that the subwoofer be capable of moving even more air—for example, one-hundred eighty cubic inches of air. A typical fifteen inch diameter woofer, which has a cone diameter of approximately thirteen inches and a stroke of approximately 0.6 inches, can move approximately eighty cubic inches of air. Therefore, generally a prior art subwoofer will utilize two of these drivers; and two drivers are able to move approximately one-hundred sixty cubic inches of air. One disadvantage of having a driver with a fifteen inch cone is that it is difficult to design a cone of that size which is rigid enough to resist distortion when the cone has such a large surface area.
Another example of a prior art subwoofer utilizes four twelve inch drivers. Each of these drivers has a cone diameter of approximately ten inches and a stroke of approximately 0.6 inches. Such a subwoofer can move approximately one-hundred ninety cubic inches of air. However, such a subwoofer suffers from the disadvantage that four drivers are required; and, this greatly increases the size of the cabinet required, cost and weight.
Of course, it is possible to increase the stroke of the driver, and thus increase the amount of air that is moved by the driver. However, when the stroke of the driver is increased, the efficiency of the driver is substantially reduced, as less of the voice coil will remain in the magnetic gap.
Prior art subwoofer systems invariably require a large cabinet. One reason, as seen from the above, is that many prior art subwoofer systems utilize several large drivers so that they can move enough air for adequate performance. However, large cabinets are necessary for prior art subwoofers for reasons having nothing to do with the number of drivers installed therein. Some of the more significant reasons for this are set forth herein below.
Drivers for subwoofers are generally installed in a sealed or vented box. Thus, when the cone of the driver moves, it must overcome the forces inherently created because of the box structure itself. For instance, during operation, if the cone is moving into the cabinet, the air inside the cabinet will be compressed by the moving cone, thereby creating a force resisting inward cone movement. If, on the other hand, the cone is moving out of the cabinet, a vacuum is created that, in effect, exerts a force tending to pull the cone back into the cabinet. These conditions exist for both sealed and vented boxes or cabinets. Atmospheric pressures outside the cabinet also affect these forces.
The driver must overcome the foregoing forces during movement of the cone. The higher the pressure to be overcome (whether positive or negative), the more power that is required to overcome that pressure. The physical structure of the subwoofer can be manipulated to deal with the increase in power that is required to overcome the foregoing forces. First, a larger enclosure (i.e., cabinet) can be used. A larger enclosure will create less resistance to inward and outward cone movements because it contains more air than a smaller enclosure. The reason for this is that when the driver cone moves into the cabinet, the larger air volume is compressed to a lower pressure. Thus, less power is required by the voice coil to overcome the forces created by the compression of air within the cabinet. Further, when the driver cone moves out of the cabinet, less vacuum is created, which therefore allows the voice coil to move the cone with less power. Because of this, prior art subwoofers have typically utilized relatively large cabinets.
A second design factor is related to the stroke of the driver. If the stroke of the driver is short, the driver cone will have physical limitations on how far it can enter into the cabinet and how far it can extend outwardly from the cabinet. The shorter the extension of the driver cone into the cabinet, the less air that will be compressed within the cabinet. Such a movement will, therefore, require less power into the voice coil to effectuate movement of the cone. The same holds true for cone extension out of the cabinet. The shorter the extension of the driver cone out of the cabinet, the less will be the vacuum that is created and, therefore, the less power that will be required for such cone movement.
Power in prior art subwoofer systems must be provided by power amplifiers. Often a subwoofer system will use a separate power amplifier. However, for ease of packaging, many prior art subwoofer systems utilize power amplifiers that are built into the cabinet of the subwoofer. In general, power amplifiers capable of driving conventional prior art subwoofers must be large and capable of creating between one-hundred (100) to three-hundred (300) watts of power. Large amounts of power are required to drive a subwoofer for many of the reasons described above. However, power amplifiers capable of providing such power levels tend to create large amounts of heat which, in turn, requires large heat sinks, massive power reserve capacitors, and large transformers, all of which are large in size, heavy, and expensive. All of these factors are undesirable; and, all tend to reinforce the need for a relatively large cabinet.
Thus, as can be seen from the foregoing, because of the large power demands required by subwoofer systems and the large cost involved in providing large amounts of power amplification, prior art subwoofer apparatus have invariably required, and utilized, large cabinets which held drivers having large diameters and short strokes. Such an arrangement, as discussed above, allowed the subwoofer to move reasonable amounts of air without distortion. However, normal listening environments often do not have space for such a large cabinet. Therefore, there is a need for a subwoofer system capable of producing low frequency information at high listening volumes that is packaged in a small volume cabinet.
The design of audio woofers has, for many years, been predicated on conventional wisdom commonly referred to as “Hoffman's Iron Law” which provides:
Eff.=VBOX/f0
where f0 is the desired low frequency cutoff or limit-for the subwoofer; VBOX is the volume of the cabinet; and, Eff. is the efficiency of the subwoofer. Unfortunately, if one wishes to reduce the low frequency cutoff (f0) from, for example, 50 Hz to 18 Hz while retaining the same efficiency, the volume of the woofer cabinet must be significantly increased. Or, if one wishes to decrease box volume from, for example, 1 ft3 to 0.4 ft3 and, at the same time, decrease the low frequency cutoff (f0) from, for example, 50 Hz to 18 Hz, efficiency drops by a factor of approximately 53. Consequently, the woofer designer finds that where a 50 watt or 100 watt amplifier might have operated a 1 ft3 woofer at a 50 Hz low frequency cutoff, a 0.4 ft3 box at 18 Hz low frequency cutoff will require an amplifier that is approximately 53 times larger than conventional.
For example, a typical loudspeaker in a 1 ft3 box with a low frequency cutoff of 50 Hz and one percent (1%) efficiency will normally operate satisfactorily if it employs a 200 watt amplifier. But, were the designer to arbitrarily decide to reduce the box volume to 0.4 ft3 and the low frequency cutoff to 18 Hz, the wattage requirement for the amplifier would be 10,600 watts. That, of course, would be ludicrous and is neither practical, cost effective nor economically feasible from a commercial standpoint.
In essence, Hoffman's Iron Law forbids one from making a subwoofer having a small volume box, high efficiency and low frequency cutoff; and, designers of subwoofers have not deviated from religious adherence to such theories. If the speaker designer wants to have a highly efficient bass driver for a highly efficient woofer that can have a very low frequency cutoff, the box must be huge—and, they always are. Conversely, if the designer wishes the box to be small, there has heretofore been no way to get a lot of bass out of it, either low or loud, with high efficiency.
At the same time, speaker designers have been taught, and have believed, that there is an optimum size for magnets employed in voice coil driven woofers—i.e., it has been assumed that if the magnet is too small, the speaker will not work at all; but, if the magnet is too large, only a small percentage of the output wattage from the power amplifier will be applied to the voice coil. Consequently, woofer designers have concluded that an optimum magnet must lie somewhere between “too small” and “too large” in order to produce effective power in the voice coil. Typically, therefore, virtually all conventional subwoofers will employ a magnet that weighs on the order of only about 20 ounces or less. Indeed, even in the face of today's highly advanced technologies, speaker designers still believe that a well designed, commercially marketable subwoofer should employ: i) a relatively large cabinet—e.g., from about eight to about twenty-seven ft3; ii) multiple large drivers; iii) drivers with peak-to-peak strokes generally on the order of not more than 0.4″ to 0.6″;
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- iv) magnets weighing, on average, not more than 20 ounces and, at the very most, about 40 ounces; v) low internal box pressures of on the order of only about 0.1 Ilbs/in2; and, vi), surrounds or suspension systems that are very compliant leading to surrounds that are, at best, flimsy and incapable of stably supporting the moving driver components without wobble and consequent degradation of the audio sounds generated.
The problem of attempting to design a woofer which is small in size—e.g., defining an enclosed volume of space of about 0.4 ft3 to about 0.5 ft3 having a low cutoff frequency below about 40 Hz, and which is, at the same time, efficient, has defied solution—at least until the advent of the present invention and the invention disclosed in Applicant's aforesaid co-pending U.S. patent application Ser. No. 08/582,149, filed Jan. 2, 1996, now U.S. Pat. No. 5,748,753 issued May 5, 1998. For example, as stated by Louis D. Fielder of Dolby Laboratories, Inc. and Eric M. Benjamin in an article entitled “Subwoofer Performance for Accurate Reproduction of Music”, J. Audio Eng. Soc., Vol. 36, No. 6, June 1988, pages 443 through 454 at page 446:
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- “For the required value of 0.0316 acoustic W at 20 Hz, this results in a volume excursion of 41.8 in3 (685 cm3). For a single 12-in (0.3-m) woofer effective piston diameter 10 in (0.25 m) this would require a peak linear excursion of 0.53 in (13.5 mm). This large excursion requirement can be reduced by using larger drivers, increasing the number of drivers, and utilizing the low-frequency boost provided by the room. With four 15-in (0.38-m) woofers the peak linear excursion required is 0.078 in (2 mm), neglecting room effects.”
In short, the “solution” advocated by the authors, who are accredited experts that were then attempting to establish design criteria for the performance of subwoofers to be used for the reproduction of music in the home, is: i) to design a woofer having a peak linear excursion of 0.53″; ii) to attempt reduce this “large excursion”—i.e., 0.53″—by using larger drivers and increasing the number of drivers (and, therefore, the size of the box or subwoofer cabinet); and iii), utilizing the low frequency boost provided by the listening room.
Those skilled in the art relating to subwoofers will recognize that the efficiency of a subwoofer is proportional the size of the box or cabinet that the subwoofer is mounted in. Therefore, a box or cabinet that is {fraction (1/10)}th the size of a conventional prior art subwoofer box or cabinet would ordinarily be ten times less efficient than its prior art counterpart. Under those circumstances, ten times more heat is developed in the voice coil regardless of the efficiency of the driving amplifier. Consequently, the voice coil will soon overheat; and, in fact, that has been a major stumbling block to the development of very small, but powerful, subwoofers. Nevertheless, as will become apparent from the ensuing description, the present invention relates specifically to a subwoofer characterized by its high efficiency and, at the same time, its extremely small box or cabinet.
The broad concept of the present invention, in fact, flies in the face of all known subwoofer computer modeling programs as well as the teachings in the prior art literature.
In this connection, those skilled in the art will appreciate that raw driver efficiency is expressed as:
Eff.=(Bl)2/re [2]
where “B” is the magnetic field strength, and “1” and “re” are constants.
Rewriting equation [2] it is found:
Eff.=kB2 [3]
Based upon the foregoing, those skilled in the art will understand that in a subwoofer driver where B is increased by a factor of 3.3, the efficiency will be increased by a factor of approximately 10—viz., 3.32≅10. Unfortunately, however, when such a subwoofer driver is built and installed in a box—any box—bass output is found to be actually far less than before the magnetic field was increased! This fact is well known to those skilled in the subwoofer art; and, consequently, prior art conventional subwoofers have evolved with magnetic fields optimized for maximum bass output.
Unfortunately, subwoofers designed with magnets optimized for maximum bass output are very inefficient. The reason for this is because the motor of the subwoofer (consisting of the voice coil and magnetic structure) is operating very close to stall, a condition characterized by relatively high armature winding—or, in the case of subwoofers, voice coil—heating. By increasing the magnetic field strength, the efficiency is increased, but the bass output is decreased because of the large back emf generated by the motion of the subwoofer's voice coil immersed in its magnetic field. The magnitude of the back emf is established by Lenze's Law:
back emf=dφ/dt, [4]
where φ is the magnetic flux.
The back emf generated acts to prevent current from flowing in the voice coil because it opposes the forward voltage impressed on the voice coil winding. With the lowered current in the voice coil, the result is less bass.
It must be recognized at this point that all prior art literature known to the inventor, the descriptive equations therein, and all subwoofer computer modeling programs based on prior art literature make the basic assumption that the subwoofer is operating in stall in order to simplify the modeling. Prior to the advent of the present invention, this assumption was tenable because a tracking downconvertor drive amplifier able to deliver the high voltage necessary to overcome the back emf did not exist. Indeed, prior art subwoofer designers have all made the simplifying assumption that the back emf at system impedance minimums is not significant.
Another major problem encountered by subwoofer designers is directly related to the fact that subwoofers are exceptionally prone to hum problems induced by power line “ground loops”. Ground loops are caused by a redundant ground that runs from the wall plug or other suitable A.C. source where the subwoofer is plugged in, through the power line to where the audio signal source—e.g., a CD player, an FM tuner, a turntable, etc.—is plugged into the power line, and then back to the subwoofer audio input through the audio cable shields. This constitutes a loop called a “ground loop”, and it generates a very undesirable 60 Hz hum.
Prior art subwoofers all suffer from unwanted “ground loop” induced 60 Hz hum to a greater or lesser degree. Subwoofer designers have attempted to solve the “ground loop” induced 60 Hz hum problem in various ways. One proposed solution includes the use of a balanced transformer which breaks the loop by virtue of its primary and secondary windings. The transformer can either be at the power line input (power transformer), or at the audio input (input transformer), or, for that matter, at both locations. Another attempted solution involves the use of optical couplings in which the audio signal is coupled by a light beam—i.e., there is no ground connection. Both of the foregoing approaches have been effective in substantially reducing, but not eliminating, “ground loop” induced 60 Hz hum problems. This is because while they effectively “break” the ground(s), they do not suppress the hum voltage generated across the broken ground or grounds.
SUMMARY OF THE INVENTIONThe present invention overcomes the foregoing problems and disadvantages inherent in the design, construction and operation of conventional prior art subwoofers by providing a subwoofer design that is characterized by: i) a relatively small volume sealed cabinet—e.g., a cabinet defining an enclosed volume of space on the order of from about only 0.4 ft3 to about only 0.5 ft3; or, substantially less than 1 cubic foot in volume in the exemplary apparatus illustrated (stated differently, the present invention requires a subwoofer cabinet which ranges from only about {fraction (1/15)}th to about {fraction (1/67)}th the size of the cabinets employed in conventional prior art subwoofers)—ii) a single voice coil driven woofer; iii) a mass driven woofer, sometimes referred to in the art as a “passive radiator”; iv) a relatively small, compact, power amplifier capable of delivering 2,700 watts rms to a 3.3 ohm (the resistance of the voice coil) resistive load (hereinafter, a “nominal 4 ohm resistive load”) and swinging 104 volts rms; and v), an arrangement wherein the maximum peak-to-peak excursion of each of the voice coil driven woofer and the mass driven woofer is on the order of about 2.5 inches as contrasted with prior art drivers having peak-to-peak strokes ranging from only about 0.4″ to about 0.6″—i.e., an arrangement wherein the maximum stroke of the drivers of the present invention is from about five to about six times greater than achievable with conventional prior art subwoofer driver configurations.
As a result of the foregoing, a subwoofer embodying features of the present invention is characterized by its extremely small size, high efficiency, high power and high acoustically accurate sound levels, all without requiring large, heavy and costly heat sinks and/or storage capacitors.
It is a general aim of the present invention to provide a small, compact, fully contained subwoofer capable of generating high quality, low distortion, and low frequency audio signals at high listening volumes, yet which is packaged in an aesthetically pleasing small volume cabinet.
More specifically, it is an object of the invention to provide a subwoofer capable of generating acoustically accurate low frequency audio signals at high listening volumes packaged in a relatively small volume cabinet.
A related object of the invention is the provision of a subwoofer having a relatively small volume cabinet, yet which has power and sound characteristics at least equal to, if not substantially better than, conventional prior art subwoofers despite the fact that the subwoofer is only a fraction of the size, weight and cost of similarly performing, commercially available, subwoofers. In achieving this objective, the subwoofer of the present invention, including its electronic packages or circuit boards, is generally fully contained in a cabinet occupying a total volume of space significantly less than 1 cubic foot—e.g., from only about 0.4 ft3 to only about 0.5 ft3—rendering the subwoofer unobtrusive to the user and facilitating easy placement of one or more subwoofers in a listening room or in other living areas within a user's residence, office or like facility.
In one of its more detailed aspects, it is an object of the invention to provide a relatively low cost subwoofer apparatus capable of equaling or exceeding the performance characteristics of conventional large and more expensive subwoofers; and, which is compact, light weight, aesthetically attractive in appearance, and devoid of large heat sinks, massive power reserve capacitors, large transformers, and the like.
A further objective of the present invention is to provide a subwoofer apparatus which, despite its small size employing a cabinet having a sealed volume of space substantially less than 1 cubic foot, is highly efficient and capable of moving or displacing large volumes of air—e.g., a volume of just under 200 cubic inches of air—in response to driver movement through a peak-to-peak stroke of up to about 2.5″.
In another of its important aspects, it is an object of the invention to take advantage of the high back emf generated by using a relatively large magnet—e.g., a magnet weighing on the order of 225 ounces (approximately 14 pounds, 1 ounce) or, approximately an order of magnitude greater than the magnets commonly used in conventional subwoofers—to oppose current flow in the voice coil of a voice coil driven woofer so as to enable employment of a small compact tracking downconvertor drive amplifier capable of outputting on the order of about 2,700 watts rms to a nominal 4 ohm resistive load and capable of swinging 104 volts rms; and, which will, therefore, deliver only about 150 to 200 watts (300 to 400 watts on a time limited basis) maximum power to the voice coil, preventing overheating thereof and enabling generation of large quantities of power with high efficiency. The use of such a large magnet roughly ten times the size of conventional prior art subwoofer magnets serves to increase the field strength of the subwoofer by a factor of 3.3 since field strength increases roughly as the square root of the magnet size.
Stated differently, in one of its important aspects it is an object of the invention to provide a subwoofer design employing a very small cabinet and a unique tracking downconvertor drive amplifier which is capable of generating sufficient power applied to the subwoofer's voice coil to overcome the excess high back emf generated by the use of a large magnet in combination with maximum voice coil peak-to-peak strokes of about 2.5″. As a result of attaining this objective, sufficient current flows in the voice coil to produce the desired bass output; and, the subwoofer's efficiency is increased by a factor of approximately 10, effectively offsetting the loss of a box volume related efficiency.
A further objective of the invention is to provide a subwoofer capable of operating far from the stall mode—viz., an operating mode characterized by very little output power and large amounts of current flowing in the voice coil generating large amounts of heat that must be dissipated—wherein the subwoofer is characterized by high conversion efficiency and low joule (voice coil) heating.
Yet another important objective of the invention is the provision of a subwoofer capable of achieving an 18 Hz low frequency cutoff in a small box 11″×11″×11″ having an enclosed volume of space of from about only 0.4 ft3 to only about 0.5 ft3 with high efficiency and at low cost. In achieving this objective, advantage is taken of the usage of a mass driven woofer (sometimes referred to as a “passive radiator”) in combination with a voice coil driven woofer made in accordance with the present invention, thus reducing size, weight and cost of the overall subwoofer.
In another of its important aspects, it is an object of the invention to provide methods for forming a surround for a subwoofer which is capable of standing off pressures ranging upwardly to about 3 pounds per square inch (3 lbs/in2)—for example,—from on the order of about one and a half pounds per square inch (1.5 lbs/in2) to about 3 pounds per square inch (3 lbs/in2)—and the resulting surround—all as contrasted with conventional surrounds which are typically capable of standing off pressures of only about 0.1 lbs/in2 to 0.2 lbs/in2; or, an improvement of up to thirty times the capability of conventional surrounds.
A further and more detailed objective of the invention is the provision of improved buffer circuitry for processing audio signals which sums both the L+R and L−R audio signal components, retaining the L−R components (which are typically destroyed in a conventional subwoofer's audio signal processing system) as part of the composite output signal, thereby enhancing the life, luster, depth and impact of the audio sound for the listener.
Another detailed object of the invention is the provision of improved protection circuitry for essentially eliminating distortion resulting from clipping, overheating, overdrive, or impulsive wave forms.
Yet another important objective of the present invention is the provision of circuitry which completely eliminates both undesirable “ground loops” and the voltage generated across broken grounds, thereby completely eliminating the problem of “ground loop” induced 60 Hz hum.
It is a further object of the invention to provide a system for maintaining tinsel leads under tension during peak-to-peak reciprocation of the subwoofers' voice coil driven components so as to prevent undesired noise resulting from slapping of the tinsel leads against the speaker cone in the voice coil driven woofer.
DESCRIPTION OF THE DRAWINGSThese and other objects and advantages of the present invention will become more readily apparent upon reading the following Detailed Description and upon reference to the attached drawings, in which:
While the present invention is susceptible of various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that it is not intended to limit the invention to the particular forms of the invention disclosed; but, on the contrary, the intention is to cover all modifications, structural equivalents, equivalent structures, and/or alternatives falling within the spirit and scope of the invention as expressed in the appended claims. Thus, in the appended claims, means-plus-function clauses and similar clauses are intended to cover: i) the structures described herein as performing a specific recited function; ii) structural equivalents thereof; and iii), equivalent structures thereto. For example, although a nail and a screw may not be deemed to be structural equivalents since a nail employs a cylindrical surface to secure wooden parts together while a screw employs a helical surface, in the art broadly pertaining to the fastening of wooden parts, a nail and a screw should be deemed to be equivalent structures since each perform the recited fastening function.
DETAILED DESCRIPTION Turning now to the drawings, exemplary embodiments of the present invention will now be described. Thus, referring first to
In carrying out the invention, the cabinet 51 is a substantially cubic structure with: i) a front wall (not visible in
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- iv) a top wall 59; and v), a bottom wall (not visible in
FIG. 1 ), all preferably constructed of a rigid, non-resonant, inert material such as MDF type particle board, wood, or the like. Each panel or wall can have a suitable finish applied thereto such that the subwoofer can match the furnishings of the room where it will be installed. The drivers 52, 54 may, if desired, be covered by an acoustically transparent material (not shown).
- iv) a top wall 59; and v), a bottom wall (not visible in
It will be noted upon inspection of
The front, rear, side, top and bottom panels (i.e., sidewalls 55, 56, rear wall 58, top wall 59, and the front and bottom walls which are not visible in
In accordance with one of the important aspects of the present invention, and as hereinafter described in connection with
It will be noted upon inspection of
Considering next
The movable components of the voice coil driven woofer 54 comprise: i) an expanded synthetic cellular foam surround 78′ such, for example, as an expanded cellular polyethylene (“PE”) foam surround, which is substantially identical to the surround 78 employed with the mass driven woofer 52 previously described except that the central disk-shaped portion 82 of the surround 78 associated with the mass driven woofer 52 has been removed in the surround 78′ employed with the voice coil driven woofer 54; ii) a speaker cone 100 having a funnel shape with its outer large diameter end 101 being adhesively bonded or otherwise fixedly secured to the inner inturned flange 81 on the surround 78′; iii) a cylindrical voice coil former 102 having an inner diameter slightly greater than the outer diameter of the annular pole piece 98;
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- iv) a voice coil 104 wound about the voice coil former and having an outer diameter slightly less than the inner diameter of the upper annular spacer 92; v) a rigid dust cover or surround support 105 having a shape comprising a segment of a sphere which is positioned within, and secured to, the funnel-shaped speaker cone 100 with the domed portion of the dust cover/support facing outwardly; vi) a decorative cover 106 formed of expanded cellular polyethylene (“PE”) surround foam, or similar material, positioned within, and secured to, the outermost large diameter end 101 of the speaker cone 100 with the decorative cover 106 abutting the dust cover/support at their respective midpoints; and vii) and annular spider 108 having a corrugated cross section wherein the depth of the corrugations progressively increase from the inner periphery towards the outer periphery with the spider 108 being secured at its innermost periphery to the outer surface of the voice coil former 102 and at its outer periphery to the frame or cage 90 of the apparatus.
Thus, the arrangement is such that when positive or negative voltage levels are output from the tracking downconvertor drive amplifier (not shown in
Thus, the movable voice coil former 102 and voice coil 104 move axially within the magnetic gap 99 between the annular pole piece 98 and the annular upper spacer 92 with a PUSH/PULL movement dependent upon the polarity of the voltage applied to, and the current flow in, the voice coil 104. Since the voice coil former 102 and voice coil 104 reciprocate axially within the magnetic gap 99—i.e., move to the left and to the right as viewed in
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- i) permitting a peak-to-peak stroke of the movable driver components of up to about 2.5″; ii) resisting or standing off internal box pressure ranging up to about 3 lbs/in2—in the exemplary embodiment of the invention, from about 1.5 lbs/in2 to about 3 lbs/in2 (an internal box pressure which, when applied to a typical 8″ diameter speaker cone 100, translates to a force of approximately 150 lbs. applied to the speaker cone (100); and iii), simultaneously supporting and stabilizing the moveable driver components on the longitudinal axis passing through the magnetic gap 99 without significant or meaningful wobble.
It will further be noted that an accelerometer 109 is mounted in the speaker cone (100) on the end of the voice coil former 102. The accelerometer 109 serves to sense the movement of the movable components of the voice coil driven woofer 54 and any movement distortion, with signals representative of such movement and any such distortions being conveyed to the processing circuitry discussed hereinafter.
Referring next to
Turning next to
The surround 78′ described above is intended for use in supporting a speaker cone 100 having an effective 8″ diameter which would normally be mounted in a basket-like frame or cage 90 having a diameter of approximately 10″. When the surround is intended for use with, for example, a speaker cone 100 (
Conventional surrounds are, and have been, typically fabricated from, for example, an expanded cellular polyethylene (“PE”) surround foam sheet which is approximately {fraction (7/16)}″ in thickness and which is compressed to form a very resilient, compliant suspension member having a thickness of approximately 0.02″. Such conventional prior art surrounds are very thin and flexible, often having little more rigidity than rubber gloves; and, consequently, have very little ability to stand off internal pressures within the woofer box 51. However, since conventional woofers generally generate internal pressures of only on the order of about 0.1 lbs/in2 to about 0.2 lbs/in2, and normally have peak-to-peak strokes of only 0.4″ to 0.6″, the conventional thin, highly flexible, compliant prior art surrounds have generally been acceptable. Typically such conventional surrounds will have an outer half roll or “edgeroll” of not more than, and usually less than, one inch in diameter.
As will be described hereinbelow, the mass driven woofer 52 and voice coil driven woofer 54 of the present invention are driven through peak-to-peak excursions up to about 2.5″ as contrasted with conventional woofers which typically have peak-to-peak excursions ranging from only about 0.4″ to about 0.6″—i.e., the movable components of the drivers 52, 54 of the present invention are driven to excursions ranging from five to six times the excursions typically generated in conventional subwoofers. Moreover, subwoofers made in accordance with the present invention generate internal box pressures up to about 3 lbs/in2—in the exemplary form of the invention, from about 1.5 lbs/in2 to about 3 lbs/in2—as contrasted with internal box pressures of only 0.1 lbs/in2 to about 0.2 lbs/in2 for conventional subwoofers—i.e., the internal box pressures that must be withstood by the surrounds 78, 78′ of the present invention range from fifteen to thirty times greater than the internal pressures generated in conventional subwoofers. Accordingly, conventional surrounds are simply not capable of standing off the pressures generated and/or supporting the movable driver components free of wobble and in a stable, but axially reciprocable, position wherein the voice coil former 102 and the voice coil 104 wound thereabout are capable of moving axially within the magnetic gap 99 through a peak-to-peak stroke of up to about 2.5″ without touching either the annular pole piece 98 or the surrounding magnet/spacer 94/92 structure.
In accordance with one of the important aspects of the present invention, the surrounds 78, 78′ of the present invention have been modified in two significant respects as compared with conventional surrounds. Although made of an expanded synthetic cellular foam such, for example, as an expanded cellular polyethylene (“PE”) surround foam which is typically supplied in sheets {fraction (7/16)}″ thick, the finished surrounds 78, 78′ of the present invention are, for an 8 inch speaker, preferably a minimum of about 0.1″ in thickness ranging up to 0.14″ in thickness or more—i.e., from five to seven times the thickness of a conventional surround for eight inch and larger conventional subwoofers. Secondly, the half round or “edgeroll” 80 of the surrounds 78, 78′ employed with the present invention have an outside diameter of approximately 1.5″ as contrasted with conventional surrounds which typically have an edgeroll of not more than, and usually less than, 1.0″ in outside diameter.
In order to carry out this aspect of the invention, and as best shown in
Those skilled in the art will, of course, appreciate that the pressure, temperature and time parameters set forth hereinabove can be varied somewhat without departing from the spirit and scope of the invention as expressed in the appended claims. However, it has been found that excellent results can be obtained on a consistent replicable basis where: i) pressure is maintained in the range of from about 60 psi to about 100 psi with about 80 psi being preferable; ii) temperature is maintained in the range of about 420° F. to about 450° F.; and iii), time is maintained in the range of from about forty (40) seconds to about ninety (90) seconds. Surrounds 78, 78′ embodying features of the present invention, and made in accordance with the methods of the present invention, have been manufactured by Rapid Die & Molding Co., Inc. of Schiller Park, Ill., to specifications originated and developed by the inventor using tooling proprietary to the inventor.
The process and product parameters for manufacturing conventional single ply surrounds using a single layer of expanded cellular polyethylene (“PE”) surround foam of approximately {fraction (7/16)}″ in thickness to produce highly resilient compressed surrounds with thicknesses of not more than about 0.02″ and a half round or “edgeroll” of not more than 1.0″ O.D. using an RDM2102 press (without the modifications required for the practice of the present invention) are proprietary to, and the property of, Rapid Die & Molding Co., Inc.; and, no claim is, or will hereafter be, made herein and/or in any future application filed by or on behalf of the inventor which would interfere with Rapid Die & Mold's exclusive right to use its pre-existing proprietary processes, information and technology; but, such prior processes, information and technology may not be modified so as to enable Rapid Die & Mold and/or others to manufacture surrounds 78, 78′ embodying features of the present invention and/or in accordance with the processes of the present invention—i.e.,: i) surrounds 78, 78′ employing half rolls or “edgerolls” 80 having diameters of approximately 1.5″; and/or ii), surrounds 78, 78′ having a substantially uniform thickness on the order of about 0.1″ or greater formed from either; a) multiple layers 118a-118n of an expanded synthetic cellular foam such, for example, as an expanded cellular polyethylene (“PE”) surround foam, and/or from other similar natural or synthetic materials, aggregating on the order of approximately 2{fraction (3/16)}″ thickness or greater prior to compression; or b), a single layer 118 of such material having an initial thickness equal to or greater than on the order of approximately 2{fraction (3/16)}″. The resulting surround 78, when removed from the press 114, exhibits the characteristics and dimensions of the surround as shown in
Directing attention now to
Thus, in carrying out the present invention, and as best shown in
The Input Buffers 125 output a composite audio signal 126 containing both the L+R and the L−R components of the signal successively to: i) a Ground Loop Hum Eliminator 124; ii) a Subsonic Filter 130, iii) an E.Q. Amplifier 131; iv) a Video Contour Controller 132; v) a Phase Amplifier 134; vi) a Crossover Control circuit 135; vii) a Volume Control 136; viii) a Line Amplifier 138; ix) an Opto-Coupler 139 (which serves to further isolate the electronics within the subwoofer 50 from the environment outside the subwoofer cabinet 51); and x), a Master Protection Circuit 140. The Subsonic Filter 130, E.Q. Amplifier 131, Video Contour Controller 132, Phase Amplifier 134, Crossover Control circuit 135, Volume Control 136, Line Amplifier 138 and Opto-Coupler 139 are all completely conventional circuits well known to persons skilled in the art and will not be described herein in further detail. Those interested in acquiring more detailed information with regard to such conventional circuits are referred to Appendix “B”.
The Master Protection Circuit 140 illustrated in block-and-line form in
Of the foregoing processing and control circuits, the Excursion Limiter circuit 142 (
In keeping with the invention, the thus processed audio signal output from the Impulse Damper 145 (
The audio signal which is output from the Woofer Servo 155 is, as best shown in
The present invention solves this problem by “steering” the positive components of the audio signal to the (+) Tracking Downconverter Power Supply 170 while the negative voltage components are steered to the (−) Tracking Downconvertor Power Supply 180. The (+) and (−) Tracking Downconvertor Power Supplies 170, 180 respectively output the (+)v. output signals and the (−)v. output signals to the Driver Amplifier 190 which also receives the composite audio signal from the Diode Steering Network 165. As a consequence of this arrangement, the Driver Amplifier 190 is enabled to deliver amplified positive voltage levels to the voice coil 104 during positive swings of the audio signal; and, thus drive the voice coil driven woofer 54 through a PUSH stroke of up to about 1.25″. Similarly, the (−)v. signals input to the Driver Amplifier 190 enable the latter to feed amplified negative voltage levels to the voice coil 104 during the negative-going portions of the audio signal, thus driving the voice coil driven woofer 54 through a PULL stroke of up to about 1.25″, with the total peak-to-peak PUSH/PULL stroke being up to about 2.5″.
As previously discussed, the output of the Diode Steering Network 165 (
Turning now to
In order to permit operation of the electronic circuits employed in the subwoofer 50 (
The power delivered to the driver of the voice coil driven woofer 54 by the inductors L1, L2 in respective ones of the Power Output Sections 174, 184 of the (+) and (−) Tracking Downconvertor Power Supplies 170, 180 is controlled by controlling the time within which the Switches 172, 182 in the respective Downconvertors 170, 180 are CLOSED for each current pulse. This is accomplished by tracking the audio signals which are to be amplified by the Driver Amplifier 190; and, comparing these tracked signals to the voltage imposed across the Driver Amplifier 190. This produces a control signal which controls the duration of each current pulse delivered to the respective inductors L1, L2. In other words, on the assumption that the Switches 172, 182 are being opened and closed at a frequency of 100 Kilohertz, the duration of each time period would be 10 microseconds. During those time periods where the power requirements of the Driver Amplifier 190 are high, then during each 10 microsecond time period, a respective one of the Switches 172, 182 will be CLOSED (dependent upon whether the polarity of the audio signal is then positive or negative) for a relatively large fraction of that time—e.g., for about 5 to about 7 microseconds. On the other hand, when power requirements of the Driver Amplifier 190 are relatively low, the respective Switches 172, 182 will be CLOSED in each time period for a much shorter duration.
As discussed above, the audio signal containing the low frequency information which is to be reproduced by the subwoofer 50 ultimately enters the Diode Steering-Network 165 (
The output of the Diode Steering Network 165 is then directed to the Comparator 176 in, for example, the (+) Tracking Downconvertor Power Supply 170. The Power Output Feedback circuit 175, which is responsive to the voltage impressed across the power input terminals of the Driver Amplifier 190, transmits a voltage generally proportional to the voltage at the power input terminals of the Driver Amplifier 190 as a second input to the Comparator 176. The Comparator 176 then “compares” the signal input from the Diode Steering Network 165 and the signal input from the Power Output Feedback circuit 175 to produce a control signal 214 (
Referring next to
In keeping with the broad objectives of the present invention, the Pulse Generator 200 associated with the (+) and (−) Tracking Downconverter Power Supplies 170, 180 illustrated in
The output pulse wave 215 (
The output wave form 216 from the Square Wave-To-Triangular Wave Converter 201 is then transmitted to the Ramp Time Modulators 171, 181 of the respective (+) and (−) Tracking Downconvertor Power Supplies 170, 180. As previously described, the Ramp Time Modulators 171, 181 also receive the control signal 214 from their respective Comparators 176, 186. This is illustrated in
The output of the Ramp Time Modulators 171, 181 is illustrated in
The voltage pulse signals 218 depicted in
Those skilled in the art will, of course, appreciate that the foregoing description of the operation of one of the (+) and (−) Tracking Downconvertor Power Supplies 170, 180 is equally applicable to the other.
Having the foregoing in mind, a brief overview of the operation of the (+) and (−) Tracking Downconvertor Power Supplies 170, 180 will be set forth hereinbelow in terms of the block-and-line diagrams depicted in
Referring to
The arrangement is such that when an audio signal is presented at the input terminals 66 and/or 68 (
Thereafter, the low frequency audio signal which has been servoed is presented to the Diode Steering Network 165 which performs several functions. For example, and as discussed above, the Diode Steering Network 165 produces a signal output wherein the negative portions of the audio signal are directed to the (−) Tracking Downconvertor Power Supply 180, and where the positive portions of the audio signal are directed to the (+) Tracking Downconvertor Power Supply 170. For an example of this, see
In keeping with this aspect of the present invention, the Diode Steering Network 165 ensures that the positive-going and negative-going audio signals are amplified at the proper time. Thus, when the subwoofer 50 receives an audio signal to reproduce, the Diode Steering Network 165 transmits an enabling signal to the Driver Amplifier 190 via line 166 for both positive and negative swings of the audio signal. The Diode Steering Network 165 also sends the positive-going portions and the negative-going portions of the audio signal to respective ones of the (+) and (−) Tracking Downconverter Power Supplies 170, 180 via respective ones of lines 168, 169 in the manner previously described above with reference to
Since upon initial start up there is no voltage generated at the output of the Power Output Sections 174, 184 of either the (+) or the (−) Tracking Downconvertor Power Supplies 170, 180, the feedback signal provided by the respective Power Output Feedback circuits 175, 185 are zero or substantially zero. Accordingly, at start up, the Comparators 176, 186 generate a rather strong output signal 214 (
At this time, the Power Output Feedback circuits 175, 185 (
Therefore, the control signals 214 (
Those skilled in the art will readily appreciate from the foregoing description that the Comparators 176, 186 will, in effect, “track” the audio signal to maintain the voltage level impressed upon the output terminals 220, 221 of the Power Output Sections 174, 184 and which is being routed to the Driver Amplifier 190 so that the voltage level is varied in such a manner that it remains only moderately above the power requirements of the Driver Amplifier 190. In actual practice, there is generally a voltage drop across the output transistors Q1, Q2 of the Driver Amplifier 190 (
Contributing to the small size of the subwoofer 50 (
Because the (+) and (−) Tracking Downconvertor Power Supplies 170, 180 used in the subwoofer 50 of the present invention react so quickly to transients, only relatively small storage capacitors C3, C4—viz., 6.8 microfarad capacitors rather than the 10,000 microfarad capacitors typically used in the prior art—are needed for supplying the power necessitated by a rapid increase in the power requirements of the Driver Amplifier 190. The reason for this is that the power pulses 219 (
Another advantage provided by the subwoofer 50 of the operational amplifier OP6 in the Clipping Level circuit 144 as best shown in
The composite audio signal 126 output from the operational amplifier OP6 in the Clipping Level circuit 144 is next conveyed to a Manual Throttle Set circuit 148 (
In order to protect the subwoofer 50 when it gets too hot, the voltage level at the junction 151 of the Manual present invention is that the tracking downconvertor drive amplifier therein is very efficient when compared to amplifiers used in prior art subwoofers. Thus, a typical prior art amplifier (not shown) used in a conventional prior art subwoofer requires the use of large heat sinks to dissipate the heat generated by the output transistors. The reason for this has to do with conventional amplifier design. More specifically, in conventional amplifiers of similar power as the invention, the rail voltages would generally be on the order of 160 volts, leading to thermal dissipation roughly an order of magnitude greater than achieved with the present invention. When the conventional amplifier is driving the load—i.e., the driver of the subwoofer—the amplifier only uses the voltage required by the driver to produce the appropriate audio volume. If that voltage is less than the voltage provided by the power supply—which it almost always will be—the remainder of that voltage must be dissipated in the output transistors. Thus, if the audio signal requires that the driver be driven with 30 volts, the remaining 130 volts multiplied by the load current must be dissipated in the form of heat by the output transistors. If a transistor is conducting ten amperes of current, the transistor is dissipating 1,300 watts of power in the form of heat. To avoid failure of the output transistors, they must be mounted on large heat sinks which aid in the heat dissipation. A further problem, however, is that most output transistors are rated at only two-hundred watts. Consequently, the output of these devices will be current limited. This will, therefore, require the use of many output transistors, each requiring a large heat sink and, therefore, the size of the subwoofer will inherently be substantially increased.
In contrast to prior art subwoofers, the outputs of the (+) and (−) Tracking Downconverter Power Supplies 170, 180 are fixed at a much lower voltage than the power supplies used in the prior art. For example, in the exemplary embodiment of the subwoofer 50 of the present invention, the output of each of the (+) and (−) Tracking Downconvertor Power Supplies 170, 180 is maintained at six volts above the voltage required by the Driver Amplifier 190. Thus, when no audio signal is being amplified, only six volts appears across the output transistors of the Driver Amplifier 190 (
In carrying out one of the important aspects of the present invention, provision is made for: i) isolating the left and right components of the audio signal being processed from the external environment; and ii), at the same time, summing the left and right channels of the audio input signal at different decibel (“dB”) levels (rather than at the same dB levels which would effectively produce a monaural audio output where the L−R component of the audio signal is effectively cancelled and lost), thereby retaining the L−R component of the audio signal representing the stereo sound field which serves to substantially enhance the life, luster, depth and impact of the audio sound for the listener. This represents a significant advance over conventional subwoofer designs wherein the L+R and L−R components are summed to monaural with equal contributions from both the left and right channel inputs, effectively canceling the L−R component of the signal and retaining only the L+R component which represents the monaural component of the signal as determined at points substantially equidistant from the left and right speakers.
To accomplish this, and as best illustrated by reference to
(L+R)+α(L−R) [5]
where α is a constant representative of the difference in resistance values for resistor R5 (680 ohms) and R6 (1,600 ohms). Because of this arrangement, the composite audio signal 126 output from the Input Buffers 125 retains the stereo sound field represented by the L−R components of the audio signal—thereby substantially enhancing the solidity and realism of the audio sound produced by the subwoofer 50.
Of course, those skilled in the art will appreciate that the values of resistors R5 (680 ohms) and R6 (1.6 K) can be reversed—i.e., resistor R5 can be a 1.6 K resistor while resistor R6 can be a 680 ohm resistor—without departing from the spirit and scope of the invention as expressed in the appended claims, in which case, the single composite audio signal 126 will be defined as:
α(L+R)+(L−R) [6]
In either case, or, for that matter, in cases where the values of the two resistors R5, R6 are other than 680 ohms and/or 1,600 ohms, provided only that they are significantly different, the left and right channels of the audio input signal will be summed at different dB levels, thereby producing the desired results—viz., outputting a composite audio signal 126 that retains both the (L+R) and (L−R) components of the audio input signal.
The composite audio signal 126—viz., either the signal (L+R)+α(L−R) or the signal α(L+R)+(L−R)—produced in accordance with one of the important features of the present invention is then fed through a Ground Loop Hum Eliminator 124 (
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- 1) A Subsonic Filter 130 which serves to strip the composite audio signal 126 of unwanted, very low frequency, inaudible signals that would, in any event, simply waste power.
2) An E.Q. Amplifier 131 which provides a slight equalization curve to ensure that the acoustic output is flat down to 20 Hz, a necessary feature because the intrinsic frequency response of the subwoofer 50 and its cabinet 51, taken together, deviates from ideal flatness.
3) A Video Contour circuit 132 having back panel adjustability via toggle switch 65 (
4) A Phase Amplifier 134 again having back panel adjustability via knob 64 (
5) A Crossover Frequency circuit 135 having back panel adjustability via knob 62 (
6) A volume control 136 defined by variable resistor VR1 having back panel adjustability via knob 61 (
7) A Line Amplifier 138 which serves to amplify the composite audio signal 126.
8) An Opto-Coupler 139 which optically couples the composite audio signal 126 to the downstream signal processing stages.
Optical coupling is highly desirable because it helps to eliminate “ground loops” and attendant hum—i.e., extraneous noise—caused by “ground loops”.
9) An Overshoot Control circuit 141 which serves to clamp any transient signals that occur to a factory predetermined maximum level
10) A Clipping Eliminator circuit 146 which serves to limit the drive signal to an absolute maximum level.
The Clipping Eliminator circuit 146 and Overshoot Control circuit 141 comprise the upstream circuits included within the Master Protection Circuit 140 (
In order to prevent the subwoofer 50 from being overdriven at frequencies below 25 Hz, the composite audio signal output from the overshoot Control circuit 141 is input, in parallel, to: i) an Excursion Limiter circuit 142 (
In carrying out this objective of the invention, and as best observed by reference to
To accomplish this, the composite audio signal 126 output from the Overshoot Control circuit 141 is applied simultaneously to both the Excursion Limiter circuit 142 (
Under those conditions where the woofer 50 is being driven to its maximum allowable mechanical limits and, nonetheless, more output is required, the Low Frequency Auto Throttle control line which is coupled to input terminal T2 of the Excursion Limiter 142 (
The output of operational amplifier OP4 comprises a negative-going signal 127 which is passed through diode D11 to charge up capacitor C9. Resistor R15 comprises a current limiting resistor which serves to protect operational amplifier OP5. Resistor R16 is provided to form a discharge path for the voltage on capacitor C9 resulting from the negative output signal 127 from operational amplifier OP4. The magnitude of the negative voltage on capacitor C9 is dependent on the amplitude of the audio input signal 126 as rectified by diodes D9, D10; and, consequently, as the negative voltage level on capacitor C9 becomes larger—i.e., more negative—than a predetermined threshold established by resistors R17, R18, operational amplifier OP5 flips HIGH, passing a positive voltage level through a current limiting resistor R20 and turning transistor Q3 ON. When transistor Q3 is turned ON, resistor R21 is pulled to ground, effectively placing resistor R22 (
Thus, those skilled in the art will appreciate that when the Low Frequency Auto Throttle circuit 143 determines that dangerously low frequencies are overstressing the subwoofer 50, the Low Frequency Auto Throttle circuit 143 is turned ON, throttling the undesirable low frequency signals. When the dangerously low frequency signals disappear, the Low Frequency Auto Throttle circuit 143 trips back to its OFF state.
In carrying out the present invention, the composite audio signal 126 output from the Excursion Limiter 142 (
When transistor Q4 is turned ON, it inserts resistor R33 in parallel with resistor R26 in the Manual Throttle Set circuit 148, reducing the output voltage at the junction 151 by 3 dB. Consequently, the drive signal to the subwoofer 54 is, in terms of power, reduced to half of its former value, allowing the subwoofer 54 to begin to cool down. When the subwoofer 54 has cooled sufficiently, the operational amplifier OP7 in the Thermal Integrator 139 flips from HIGH to LOW as the capacitor C11 is being discharged.
The composite audio signal 126 impressed on junction 151 is then fed to the input of an Impulse Damper circuit 145 whose function and operation is described in detail below. However, before discussing the Impulse Damper circuit 135 in detail, it may be helpful to an understanding of this facet of the present invention to briefly describe the operation and relationship of the mass driven driver 52 (
“Passive radiators” are well known to persons skilled in the art; and, it will be understood that the mass driven subwoofer 52 or “passive radiator” employed with the present invention does not, of and by itself, constitute an inventive feature of the invention. Nevertheless, its structure and operation do contribute to the lightness in weight of the subwoofer 50 of the present invention and to the ability of the subwoofer to function at high efficiency in a very small cabinet 51. More specifically, and as is well known to persons skilled in the art, assume that operation of the subwoofer 50 is initiated when the movable components of both the mass driven subwoofer 52 and the voice coil driven subwoofer 54 are initially at rest, and in the null or neutral position shown in solid lines in
Under these assumed operating conditions, it will be understood that the movable components of the voice coil driven subwoofer 54 will begin to move outwardly in a PUSH stroke of up to about 1.25″ from the null or neutral position. As the voice coil driven subwoofer's movable components begin to move outwardly, the air contained within the sealed cabinet 51 (
F=Ma=(Mdv/dt) [7]
where “M” equals the mass of the subwoofer's movable components, “a” equals acceleration, “dv” equals incremental changes in velocity, and “dt” equals incremental changes in time.
Movement of the voice coil driven subwoofer 54 is, of course, governed by the following:
F=il×{right arrow over (B)}=Bli [8]
where “i” equals the current in to voice coil 104, “l” equals the length of the voice coil 104, and “{right arrow over (B)}” equals the magnetic field.
During approximately the first half cycle of operation, the movable components of the voice coil driven subwoofer 54 and the mass driven subwoofer 52—i.e., the “passive radiator”—are out of synchronism with movement of the mass driven subwoofer 52 lagging behind that of the voice coil driven subwoofer 54. However, following the initial approximate half cycle of operation, the mass driven subwoofer 52 catches up with the voice coil driven subwoofer 54 and the movable components of the two subwoofers 52, 54 begin to move in synchronism with both moving outwardly simultaneously in a PUSH stroke of up to about 1.25″ and both moving inwardly simultaneously in a PULL stroke of up to about 1.25″—i.e., a peak-to-peak stroke of up to about 2.5″.
During the initial approximate half cycle of operation when the mass driven subwoofer 52 is still moving inwardly while the voice coil driven subwoofer 54 is moving outwardly, air pressure within the cabinet 51 is insufficient to prevent the voice coil driven subwoofer 54 from being overdriven; and, during this brief period of time, the voice coil driven subwoofer 54 can be damaged unless steps are taken to control the motion of the movable components in the voice coil driven subwoofer 54.
To resolve this problem, the composite audio signal 126 output from junction 151 in the Manual Throttle Set circuit 148 (
In order to ensure that the audio sounds emanating from the subwoofer 50 of the present invention are as free of distortion as possible, provision is made for sensing whether the moving components of the voice coil driven subwoofer 54 are moving in a linear non-distorted fashion or are moving in a non-linear distorted fashion; and, wherein distorted nonlinear motions are sensed and generate a signal which is proportional, but inverted, with respect to the sensed non-linear distorted motion of the subwoofer and are impressed on the undistorted composite audio signal 126 being processed. To accomplish this, the composite audio signal 126 output on terminal 154 of the Impulse Damper (
Acceleration of the subwoofer 54 is, in turn, proportional to the amplitude of the motion; and, consequently, when the amplitude of the motion of the subwoofer 54 is non-linear, the output of the accelerometer 109 is also non-linear. The Woofer Servo 155 serves to compare the output signal from the accelerometer 109 with the non-distorted composite audio input signal 126.
To accomplish this, the sensed output signal from the accelerometer 109—which is a replica of the motion of the voice coil 104 and other moving components of the voice coil driven subwoofer 54—is fed to an operational amplifier OP10 (
The output signal from operational amplifier OP10—which is a replica of the undistorted composite audio signal 126 being input to the positive input port of operational amplifier OP9, but which has any sensed distorted components on it amplified by operational amplifier OP10, is fed, out-of-phase with the undistorted composite audio signal 126, to the negative input port of operational amplifier OP9. Thus, operational amplifier OP9 algebraically sums the undistorted composite audio signal 126 presented at its positive input port and the distorted signal output from the accelerometer 109 and presented at its negative input port. This serves to ensure that the composite audio signal 126 output from the operational amplifier OP9 on terminal 159 is a distorted audio drive signal; but, the distortion is substantially equal and opposite to the distortion resulting from the sensed non-linear movement of the subwoofer 54. As a consequence, the distorted composite audio drive signal 126 output from the operational amplifier OP9 on terminal 159 serves to substantially cancel, to the extent possible, the distortions sensed by the accelerometer 109. Resistors R42, R43 serve to set the gain of operational amplifier OP9. Resistors R44, R45 and capacitor C14 form the compensation poles and zeros to compensate the feedback system as is conventional with Woofer Servo circuitry such as depicted at 155 in
The distorted composite audio drive signal 126 output from the Woofer Servo 155 on terminal 159 is then passed through the Buffer 160 (
In order to better understand the operation of the Diode Steering Network 165 depicted in
In order to simplify an understanding of the ensuing description of the circuit architecture and operation of the (+) and (−) Tracking Downconvertor Power Supplies 170, 180, attention is directed to FIGS. 31A-31C—but, especially,
Referring now to
As best shown in
In the Ramp Time Modulator 171, resistor R60 comprises a pull-up resistor enabling power to flow into the the light sensative trigger 178 in light emitting diode LED1, while resistor R61 is a pull-up resistor enabling power to flow into the opto-coupler 177. Capacitors C19, C20 and C22, together with diode D16, are power suppression filter components for the opto-coupler 177. A pull-up resistor R62 is provided to enable power to flow into the bases of the transistors Q6, Q7 to turn the transistors ON. Resistor R63 and capacitor C22 comprise components at the output of the driver circuitry consisting of transistors Q6, Q7 which serve to slightly slow down the drive pulses so as to avoid generating radio frequency interference (RFI). Capacitors C23, C24 are RFI suppression components.
The signal output from the Ramp Time Modulator 171 is input to the (+) Switch 172 via resistors R64, R65, R66, R67 which all comprise suppression components. Resistor R68 comprises a safety resistor to ensure that there is always a ground return path for the high impedance field effect transistors FET1, FET2, FET3. A boot strap power supply is provided by capacitor C25, resistor R69 and diode D17 when the field effect transistors FET1, FET2, FET3 are OFF. At this time, the voltage at the output of the field effect transistors FET1, FET2, FET3 is LOW; and, when this occurs, the negative end of capacitor C23 is locked to ground through diode D5 which is forward conducting during that period of time, permitting current to flow from the 13 volt supply through capacitor C25, resistor R69 and diode D17 so as to charge up capacitor C23—i.e., the charge on capacitor C25 is transferred to capacitor C23 through resistor R69 and diode D17. When capacitor C23 is fully charged and fixed HIGH, the power supply for the circuit is from capacitor C23 rather than capacitor C25, enabling current flow from capacitor C23 to run the circuitry for the Ramp Time Modulator 171. The outputs from the field effect transistors FET1, FET2, FET3 are filtered by inductor L1 and capacitor C3. The purpose of diode D5 is to supply continuous conduction when the field effect transistors FET1, FET2, FET3 are OFF. Capacitors C26, C27 comprise RF suppression components with capacitors C26 and C27 being in parallel with the +160 volt main power supply, again serving to prevent RFI.
In operation, the (+)-v output signal from the Power Output Section 174 of the (+) Tracking Downconvertor Power Supply 170—i.e., inductor L1, capacitor C3 and diode D5—are routed to: i) the Driver Amplifier 190 via output terminal 220; and ii), the (+) Power Output Feedback Section 175 which provides an input to the negative port of the (+) Comparator 176 therein. Since the audio signal input to the positive input port of the (+) Comparator has a peak voltage of only 13 volts, while the (+)-v voltage levels peak at 153 volts, the (+) Power Output Feedback Section 184 includes resistors R70, R71, R72 which comprise a voltage divider to drop the peak 153 volt (+)-v signal to in the range of about a 13 volt peak signal so that when the input signals are added together in the (+) Comparator 176, they are compatible in amplitude, value and size.
Turning now to
In accordance with another of the important aspects of the present invention, and as best seen by reference to
As a consequence, the composite audio signal 126 input to operational amplifier OP 16 is inverted at the output 234 of operational amplifier OP 16, appearing as an inverted audio signal (126), and is then fed to a light emitting diode LED2 in the opto-coupler 231, generating light which is detected by a light sensitive transistor Q13 in the opto-coupler 231. The output signal generated by transistor Q13 is then fed to the negative input port of a second inverting operational amplifier OP18. A capacitor C29 serves to couple the A.C. components of the inverted audio signal (126) at the junction 235 between the transistor Q13 and the resistor R83 to operational amplifier OP18 which serves to again invert the previously inverted composite audio signal (126), producing a non-inverted composite audio signal 126 at its output 236. Resistor R86 sets the gain of operational amplifier OP18.
At the same time, the original non-inverted composite audio signal 126 input to the Ground Loop Hum Eliminator 124 at terminal 230 is routed to the positive input port of operational amplifier OP17 which comprises a unity gain buffer, reproducing the composite audio signal 126 in noninverted form at its output 238. That audio signal 126 is then routed to light emitting diode LED3 in opto-coupler 232, generating a light signal conveyed to a light sensitive transistor Q14. The output of transistor Q14 is conveyed to the positive input port of operational amplifier OP19, a unity gain Buffer, through capacitor C30 which serves to couple the A.C. components of the signal 126 at the junction 239 between the transistor Q14 and resistor R85 to the operational amplifier OP19. The non-inverted composite audio signal 126 at the output 240 of operational amplifier OP19 is then combined with the non-inverted composite audio signal 126 at the output 236 of operational amplifier OP18 by resistors R87, R88, with the audio signal appearing at the junction 241 of resistors R87, R88 being routed to the output terminal 242 of the Ground Loop Hum Eliminator 124 as a non-inverted composite audio signal 126 to be then fed to the Subsonic Filter 130 as shown at
In the event that an undesired, unwanted “ground loop” induced 60 Hz hum voltage or signal 243 should appear across the input grounds 244 and output grounds 245, the opto-couplers 231, 232 will route the hum signal 243 to respective ones of the operational amplifier OP18, an inverting amplifier, and OP19, a unity gain amplifier. Since the non-inverted hum signals 243 at the inputs to the two operational amplifiers OP18, OP19 are in phase, the inverted hum signal (243) at the output 236 of inverting operational amplifier OP18 will be out of phase—i.e., inverted—with respect to the hum signal 243 at the output 240 of operational amplifier OP 19. Consequently, when the inverted hum signal (243) at the output 236 of operational amplifier OP 18 is combined with the non-inverted hum signal 243 at the output 240 of operational amplifier OP19 by resistors R87, R88, the two hum signals (243), 243 cancel to zero.
Thus it will be seen that the input grounds 244 and output grounds 245 are separated or isolated by the opto-couplers 231, 232, thereby “breaking” the grounds and preventing closed “ground loops”. Any hum voltage 243 generated across the broken grounds 244, 245, will be cancelled due to the phase inversion action of operational amplifier OP18 and summing resistors R87, R88. Finally, the composite audio signal 126 is not cancelled because the audio signal 126 is inverted (out of phase) by operational amplifier OP16, and then inverted a second time—i.e., reinverted—by operational amplifier OP18, so that the composite audio signal 126 at the output 236 of operational amplifier OP 18 is in phase with the composite audio signal 126 at the output 240 of operational amplifier OP19; and, when these two in phase composite audio signals 126 are combined by resistors R87, R88, a composite audio signal 126 devoid of 60 Hz hum induced by “ground loops” is produced at the junction 241 of resistors R87, R88 and is output to the Subsonic Filter 130 (
In accordance with another of the important features of the present invention, provision is made for maintaining the tinsel leads 112 (
Those skilled in the art will appreciate from the foregoing description that the subwoofer 50 of the present invention, although totally contained in a sealed cabinet 51 only 11″×11″×11″ defining an internal volume of space of only about 0.4 ft3 to about 0.5 ft3—as contrasted with conventional prior art subwoofers typically requiring cabinets enclosing a volume of space ranging from about 8 ft3 to about 27 ft3—is, nevertheless, characterized by its ability to output as much bass output as the extremely large conventional prior art subwoofers. This is possible for the following principle reasons:
Those skilled in the art will appreciate from the foregoing description that the subwoofer 50 of the present invention, although totally contained in a sealed cabinet 51 only 11″×11″×11″ defining an internal volume of space of only about 0.4 ft3 to about 0.5 ft3—as contrasted with conventional prior art subwoofers typically requiring cabinets enclosing a volume of space ranging from about 8 ft3 to about 27 ft3—is, nevertheless, characterized by its ability to output as much bass output as the extremely large conventional prior art subwoofers. This is possible for the following principle reasons:
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- 1. The subwoofer 50 of the present invention is characterized by having drivers 52, 54 capable of moving in and out of the very small woofer cabinet 51 through peak-to-peak strokes of up to about 2.5″—i.e., maximum a peak-to-peak stroke that is from five to six times greater than that achievable with conventional prior art subwoofer configurations.
- 2. The subwoofer 50 of the present invention includes a mass driven woofer 52 and a voice coil driven woofer 54 in which the movable driver components are supported solely by a flexible surround 78, 78′ and a flexible spider 89, 108. The surrounds 78, 78′ are uniquely characterized by their construction and rigidity, each having a thickness ranging from about 0.1″ to about 0.14″, or more, and an edgeroll having a diameter of about 1.5″ as contrasted with conventional prior art surrounds having thicknesses on the order of 0.02″ and edgerolls having diameters less than 1″. The surrounds 78, 78′ of the present invention are capable of withstanding internal box pressures which are an order of magnitude greater than the internal box pressures generated in conventional prior art subwoofers while retaining the movable driver components stable and substantially free of wobble as they move through their peak-to-peak stroke of up to about 2.5″.
- 3. Since the subwoofer 50 of the present invention is contained totally within a very small sealed cabinet defining an internal volume of space ranging from about 0.4 ft3 to about 0.5 ft3 i.e., a cabinet ranging from about {fraction (1/15)}th to about {fraction (1/67)}th the size of a cabinet employed in conventional prior art subwoofers—as the movable components of the mass driven subwoofer 52 and the voice coil driven subwoofer 54 move in and out of the cabinet 51, a very high air pressure is generated within the cabinet 51—viz., up to about 3 lbs/in2 and, in the exemplary form of the invention from about 1.5 lbs/in2 to about 3 lbs/in2; or, a pressure sufficient to impose a force of 150 lbs. on a typical 8″ diameter speaker cone 100 (
FIG. 3 ). Therefore, in order to overcome the high air pressure generated within the cabinet 51, a tracking downconvertor drive amplifier—viz., the (+) and (−) Tracking Downconvertor Power Supplies 170, 180 and Driver Amplifier 190—is required which is capable of: i) delivering on the order of 2,700 watts rms into a nominal 4 ohm resistive load; ii) swinging 104 volts rms; and iii) delivering only about 150 to 200 watts (300 to 400 watts on a time limited basis) maximum power to the voice coil 104, preventing overheating and enabling generation of large quantities of power with high efficiency. - 4. The weight of the magnet 94 employed with the present invention is approximately 225 oz. (i.e., approximately 14 lbs, 1 oz.)—that is, the magnet 94 employed with the present invention is approximately 512 to 11 times larger than the magnets commonly employed in prior art subwoofers where the magnet typically weighs not more than 20 ounces, and, at most, 40 ounces—and, consequently, the back emf generated within the subwoofer of the present invention is extremely high, allowing the driver 54 to be operated far away from the stall mode and, consequently, at an efficiency more than ten times greater than a conventional subwoofer of comparable size could possibly achieve.
It will, it is believed, facilitate an understanding of the present invention if a brief description is set forth at this point as to a typical subwoofer's operation relative to the stall mode and the efficiencies achieved resulting from generating a large back emf—something achievable only with subwoofers 50 embodying features of the present invention.
Virtually all, if not all, conventional prior art subwoofers are operated very close to stall—an operating mode characterized by very little output power and large amounts of current flowing through the coils of the motor—viz., the voice coil and the magnet—thus making the motor run very hot. In the present invention, however, the electric motor of the subwoofer—i.e., the voice coil 104 and magnet 94—is operated far away from the stall mode. This serves to generate a large back emf. That is, most voltage delivered to the voice coil 104 is, in effect, cancelled by the back emf generated within the motor (voice coil 104/magnet 94) by virtue of the driver's approximate 2.5″ peak-to-peak excursion.
More particularly, because the voice coil 104 is moving inwardly and outwardly with a relatively long peak-to-peak excursion of up to about 2.5″, the voice coil 104 cuts many lines of magnetic flux in the magnetic structure. As those skilled in the art will appreciate, it is the rate of flux change that generates back emf; and, consequently, the large peak-to-peak stroke or excursion of the voice coil 104 within the magnet structure not only moves large amounts of air but, more importantly, it serves to generate a large back emf. In conventional prior art subwoofers, the voice coil typically moves through a peak-to-peak stroke of only about 0.4″ to only about 0.6″—viz., the peak-to-peak stroke of the driver of the present invention is from about five to about six times greater than the maximum peak-to-peak strokes achieved with a conventional prior art subwoofer configuration—within a magnetic field generated by a very small magnet (a magnet typically weighing only about 20 oz.); and, consequently, conventional prior art subwoofers are incapable of generating a large back emf This results in too much current flow in the voice coil winding, causing the subwoofer to overheat; and, therefore, requires large, heavy and expensive heat dissipation systems.
A further requirement for generating a large back emf is the provision of a very high magnetic flux field—again a requirement that cannot be met with conventional prior art subwoofers which typically employ magnets weighing not more than 20 ounces; occasionally employing magnets weighing up to 28 ounces; and, in rare cases employing magnets weighing as much as 40 ounces. The magnet 94 employed with the present invention, however, weighs approximately 225 ounces or, it is an order of magnitude larger than magnets typically employed with conventional prior art subwoofers. Consequently, as the voice coil 104 moves within the very high magnetic flux field produced by the extremely large magnet 94 through a peak-to-peak stroke of up to about 2.5″, a large back emf is generated due to the large stroke of the voice coil 104 cutting many lines of force. This is, of course, not possible with conventional subwoofers where: i) the voice coil typically moves with a peak-to-peak stroke on only about 0.4″ to about 0.6″; ii) the magnet weighs only about 20 oz.; and iii), therefore, the magnetic flux field is small and relatively few lines of force are cut.
Thus having in mind the foregoing discussion and recognizing that: i) the voice coil 104 and magnet 94 of the present invention are operated far from the stall mode, thus generating a large back emf; ii) that the invention contemplates the use of a very large annular magnet having an O.D. of approximately 7-{fraction (11/16)}″, an I.D. of approximately 3.5″, and a weight of approximately 225 ounces, and is, therefore, capable of generating a very high magnetic flux field B; iii) the invention employs a pole piece 98 having a diameter of approximately 3″; iv) the voice coil 104 is a four-layer winding having an overall wound length of approximately 2″ and reciprocates in a magnetic gap 99 of up to about 0.25″; v) the voice coil 104 is reciprocating through peak-to-peak strokes ranging up to about 2.5″ and, therefore, cuts many lines of flux; and vi), the subwoofer 50 of the present invention is capable of operating at frequencies f as low as 20 Hz, it is relatively easy and well within the ability of persons skilled in the art, to compute comparative back emf levels for the present invention on the one hand and conventional prior art subwoofers on the other hand.
Thus, the back emf generated in a typical 8″ Dia. voice coil driven subwoofer, or driver 54, made in accordance with the present invention, operating at a frequency f of, for example, 25 Hz, and employing a magnet 94, pole piece 98, and voice coil 104 having the foregoing dimensional and/or weight characteristics, is established by:
[4]back emf=dφ/dt
where:
[9]dφ/dt=Blv=B1 A ωcos ωt
where: i) B is the magnetic flux field generated by the exemplary magnet/pole piece combination 94/98 of the present invention; ii) l is the length of the voice coil 104 in the magnetic gap 99; and iii), v is equal to velocity, where the velocity v is, in turn, equal to A ω cos ωt and A is equal to the maximum peak stroke of the voice coil 104 (i.e., one-half of the peak-to-peak excursion), ω is equal to 2πf where f is assumed equal to 25 Hz, and cos ωt is equal to 1 corresponding to the peak velocity. Consequently, in order to calculate back emf generated with the present invention assuming: (i) a frequency f of 25 Hz; and ii), a peak-to-peak stroke of 2.5″ for the voice coil 104—viz., a maximum peak stroke of 1.25″ (or 0.03175 meters)—or a peak-to-peak stroke of 2.0″ defining a peak stroke of 0.1″ (or 0.0254 meters), one skilled in the art must first compute the values of B (flux) and l(the length of the voice coil 104 wire within the magnetic gap 99).
To compute the value of flux B, one skilled in the art will recognize that the following well-known equation yields B:
B≅(A1/A2)Br [10]
where A1 is the radial or transverse surface area of the magnet 94, A2 is the radial or transverse surface area of the pole piece 98, and Br is retentivity (a value capable of being determined by reference to commonly available “look up” tables). Since the O.D. and I.D. of the annular magnet 94 and the diameter of the pole piece 98 are all known quantities, substituting in equation [10] and simplifying produces:
B≅[(7{fraction (11/16)})2−(3.5)2]/32×Br [10]
or, B≅(59−12.2)/9×Br
and, therefore:
B≅5.194(Br). [10]
However, Br (retentivity) is a known quantity. See, e.g., REFERENCE DATA FOR ENGINEERS, Seventh Edition, chapter entitled “Saturation Flux Densitys,” where the value of Br for a magnet such as the exemplary magnet 94 ranges from 0.16 to 0.24 and averages 0.20.
Therefore:
B≅5.194(0.20)≅1.0388 Teslas. [10]
In order to compute the approximate length l of that portion of the voice coil 104 in the magnetic gap 99, one skilled in the art needs to determine: i) the axial length of the magnetic gap 99 between the gap plate (top plate 92) and the voice coil 104; and ii), the length l of the wire forming that portion of the voice coil 104 in the magnetic gap 99. The axial length of the magnetic gap 99 defined by the gap plate (top plate 92) is, by definition (as well known to persons skilled in the art), one-quarter of the diameter of the pole piece 98—viz., ¼×3″ equals 0.75″. In other words, those skilled in the art will recognize that the flux density in the pole piece 98 and the flux density in the gap plate (top plate 92) must be made equal for optimum magnetic design. This means that their respective areas must be the same—i.e., A2 equals A3 where A2 is the radial or transverse area of the pole piece 98 and A3 is the inner circumferential area of the annular gap plate (top plate 92).
As to the overall length of the wire in the voice coil 104, it is known from the foregoing description that the voice coil 104 is a four-layer winding of approximately 2″ overall length; and, persons skilled in the art will know that such windings are typically formed of copper wire. Solving a simple arithmetic problem wherein the thickness of the magnetic gap (0.25″) is known, as is the overall length (2″) of the voice coil winding 104 and the fact that the winding is a four-layer winding, shows that the wire gauge must be 23 in order for the voice coil winding 104 to fit inside the specified gap, allowing the voice coil winding 104 to reciprocate in a magnetic gap 99 of up to about 0.25″ in radial width without impinging upon or rubbing against the gap plate (top plate 92) or other fixed structural components of the driver 54.
Thus, one can readily determine that the overall length of the wire defining the voice coil 104 is approximately 195 feet, or approximately 59 meters; and, since only 0.375″ of the overall 2″ length of the wound voice coil 104 is in the gap 99 at any given point in time, then the length l of the voice coil 104 in the magnetic gap 99 at any given time is 0.375″ (59) or, about 22.1 meters. Therefore, Bl≅B(1.0388 Teslas)×l(22.1 meters)≅22.9 Tesla-meters. However, those skilled in the art will appreciate that no magnetic geometry is perfect and, consequently, some lines of force will be lost. To compensate for this fact, Bl will be assumed to approximate only 19.5 Tesla-meters—viz., only about 85 percent of the theoretical value computed above.
Accordingly, substituting in equation [9]:
[9] Back emf=Bl(A)(2πf)(cos ωt); and, therefore:
[9] Back emf=19.5(0.03175)(2π25)(1)=97.25 volts peak or 68.6 volts rms (97.25×0.707) where the long excursion stroke equals 2.5″ or 0.03175 meters peak.
Alternatively, where the long excursion stroke equals 2″ and the maximum peak stroke is, therefore, 0.0254 meters, substituting in equation [9] produces:
[9] Back emf=19.5(0.0254)(2π25)(1)=77.8 volts peak or 55 volts rms.
Obviously, as the frequency f increases from the assumed frequency of 25 Hz to, for example, 40 Hz, 60 Hz, 80 Hz, etc., the back emf will increase proportionally assuming that the peak-to-peak stroke remains at 2.5″. However, in normal operation, and as a practical matter, as the frequency f increases, the peak-to-peak stroke will generally decrease from the maximum peak-to-peak stroke of about 2.5″; and consequently, while the back emf generated by the present invention may increase somewhat above 97.25 volts peak (or 77.8 volts rms) as computed above, it will not, in normal operation, increase to several hundred volts peak even where the frequency f rises to, for example, 100 Hz.
If the frequency f in the foregoing example is increased from 25 Hz to 30 Hz, and assuming the maximum peak stroke A remains at 0.03175 meters, then:
[9] Back emf=19.5(0.03175)(2π30)(1)=116.7 volts peak or 82.51 volts rms.
The significant back emf generated by the present invention becomes quite remarkable when compared to the back emf generated by a normal or standard sized prior art 8″ Dia. driver using a relatively small magnet weighing, for example, 25 ounces, having a peak-to-peak stroke of 0.6″ defining a maximum peak stroke of 0.00762 meters, and operating at a frequency f of 25 Hz. Thus, it is known that with such relatively small light-weight magnetic structures, the value of Bl will typically range from about 5 Tesla-meters to about 8 Tesla-meters. Therefore, assuming an above average Bl value of 7 Tesla-meters for such a conventional driver, and substituting in equation [9], it will be determined:
[9] Back emf=7(0.00762)(2π25)(1)=8.38 volts peak or 5.92 volts rms where the peak-to-peak stroke equals a maximum of 0.6″ and, therefore, the maximum peak stroke is 0.00762 meters.
Where the frequency f of such a conventional prior art subwoofer is increased from 25 Hz to 30 Hz, then:
[9] Back emf=7(0.00762)(2π30)(1)=10.05 volts peak or 7.10 volts rms.
Indeed, even assuming there exists a prior art 8″ Dia. subwoofer with a magnetic structure sufficiently large to generate a Bl volume of 11 Tesla-meters—a highly unlikely possibility—then:
[9] Back emf=11(0.00762)(2π25)(1)=13.16 volts peak or 9.31 volts rms
In short, the back emf generated by a conventional 8″ diameter prior art subwoofer having a relatively small light-weight magnetic structure will be only about 9.5 percent of the back emf generated by the voice coil driven driver 54 of the present invention assuming, of course, that both are being operated at the same frequency. Not even the worst case upper limit of the back emf of a conventional 8″ subwoofer falls within the back emf range of an 8″ subwoofer constructed in accordance with this invention. In that regard, assuming a situation in which a conventional 8″ subwoofer is driven to the point at which the voice coil “bottoms out” (typically about 0.8″ peak-to-peak), and assuming magnetic structure generating a Bl of 11 Tesla-meters results in a back emf of 17.6 volts peak (approximately 12.5 volts rms) at a frequency of 25 Hertz. In comparison, substituting values discussed herein that apply to an 8″ subwoofer constructed in accordance with the invention results in a range of back emf values substantially in excess of 13 volts rms up to about 100 volts rms at a frequency of 25 Hertz.
However, the large back emf generated with the use of a long peak-to-peak stroke of the voice coil 104 within a very high magnetic flux field provided by a large magnet weighing approximately 225 ounces, produces a further problem conventional prior art subwoofers are unable to cope with. That problem is related to the fact that when the back emf is very high, as it is with the present invention, the applied emf to the woofer must be even greater than the back emf in order to overcome it.
In the present invention, this problem is solved by employing an extremely powerful amplifier—viz., a tracking downconvertor drive amplifier (170, 180, 190) capable of delivering 2,700 watts rms into a nominal 4 ohm resistive load, and which can swing 104 volts rms. However, despite employment of such an extremely powerful amplifier, the woofer 50 of the present invention does not overheat and/or burn up while the moving driver components are moving in and out through the 2.5″ peak-to-peak stroke because the presence of a large back emf prevents the flow of damaging stall mode currents in the voice coil 104 that would normally flow in the subwoofer 50 if it were a simple resistive load. Rather, only a small fraction of that current flows in the voice coil 104; but, since the magnet 94 is so large and because the drive force is equal to the magnetic field times the current—See, equation [8], supra—the force on the voice coil 104 to drive the subwoofer 54 and move the air is immense even though very little current is flowing in the voice coil 104. However, where, as here, the magnet 94 is extremely large (i.e., approximately 225 ounces), the back emf generated reduces the volts available, and this leads to the need for a special tracking downconvertor drive amplifier 170, 180, 190.
In the present invention, where the subwoofer 50 operates far from the stall mode, the tracking downconvertor drive amplifier defined by the (+) and (−) Tracking Downconverter Power Supplies 170, 180 and the Driver Amplifier 190 operates at approximately 88% efficiency. This means that at an input of 200 watts, 176 watts are delivered to the voice coil 104. Indeed, at full output power, the subwoofer 50 of the present invention requires delivery of only 360 watts (for an acoustic output of 115 dB) to the voice coil 104.
In summary, the subwoofer 50 of the present invention is characterized by:
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- i) being flat to 18 Hz; ii) each driver 52, 54 can move 125 in3 of air; iii) extremely low distortion; iv) a built-in tracking downconvertor drive amplifier (170, 180, 190) capable of delivering 2,700 watts rms into a nominal 4 ohm resistive load and swinging 104 volts rms; and v), generation of a large back emf attributable to the use of an extremely large magnet (225 ounces) and a voice coil 104 moving through a peak-to-peak stroke of up to about 2.5″ in a very small cabinet 51 (approximately 11″×11″×11″) defining an enclosed volume of space ranging from only about 0.4 ft3 to only about 0.5 ft3, all of which cooperate to allow the subwoofer 50 to be operated far from the stall mode, whereas typical and conventional prior art subwoofers are deliberately designed to operate close to the stall mode wherein large amounts of current flow through the voice coil, generating a large amount of heat that must be dissipated.
Another important feature characteristic of the present invention is the use of a flexible suspension system for the movable driver components including solely a spider 89, 108 and a surround 78, 78′ wherein the surround 78, 78′ ranges from about 0.1″ to 0.14″, or more, in thickness, employs an edgeroll 180 on the order of about 1.5″ in diameter, and is capable of standing off the large internal box pressures—viz., up to about 3 lbs/in2 and, in the exemplary form of the invention, from about 1.5 lbs/in2 to about 3 lbs/in2—generated within the cabinet while permitting the movable driver components to move axially inward and outward through a peak-to-peak stroke of up to about 2.5″ in a stable manner and without significant wobble.
A further important feature characteristic of the present invention is the provision of Input Buffers 125 (
Still another important feature characteristic of the present invention is the provision of a Ground Loop Hum Eliminator 124 (
Appendices
The Inventor is appending hereto Appendices “A” and “B” more fully identified below. Such Appendices comprise schematic circuit drawings depicting in greater detail the circuitry employed with the present invention, including component identification and values. It is intended that such appendices be made a part of the file history relating to this application and, therefore, documents which are available for public inspection by interested parties. It is not intended that these Appendices be printed as part of any patent issuing from this application.
It will be understood by persons skilled in the art that appendices “A” and “B” contain materials which are deemed sensitive and highly proprietary by Applicant and his corporation—viz., Sunfire Corporation—and are not to be duplicated, in whole or in part, without the express written consent of Sunfire Corporation.
Appendix “A” comprises a size “D”, computer-generated schematic circuit drawing—viz., Drawing No. 653-010-00 dated Jan. 22, 1996, with revisions as of Mar. 26, 1997, entitled “True Subwoofer Amplifier”—here depicting circuit details, including component identifications and values where applicable, of the (+) and (−) Tracking Downconvertor Power Supplies 170, 180, Driver Amplifier 190 and Auto ON/OFF circuit employed with the present invention.
Appendix “B” comprises a size “D”, computer-generated schematic circuit drawing—viz., Drawing No. 653-011-00, dated Jan. 22, 1996, with revisions as of Mar. 19, 1997, entitled “Sunfire Subwoofer Preamp & Signal Processor”—here depicting circuit details, including component identifications and values where applicable for: i) an exemplary Signal Processing Circuit including: Input Summing Buffers 125; a Subsonic Filter 130; an E.Q. Amplifier 131; a Zero to −180° Phase Amp 134; a THX® Amp; a Crossover Frequency circuit 135; a Bass Level Control 136; Voltage Regulators; a Line Amplifier 138; an Input Opto-Coupler 139; and, a Low-Pass Filter; ii) an exemplary Master Protection Circuit 140 including: an Overshoot Control 141; a Clipping Eliminator 146; an Excursion Limiter 142; a Clipping Level circuit 144; a Low Frequency Auto Throttle 143; a Thermal Integrator 149; and, a Thermal Protection (Trip circuit) 150; and iii), an Input Woofer Servo 155.
Claims
1. A high pressure, high back emf, small volume subwoofer for processing an input audio signal and comprising, in combination:
- a) a cabinet having front, rear, left, right, top and bottom walls defining a sealed box enclosing a volume of space of less than 1 ft3 with coaxial openings formed in said left and right walls;
- b) first and second basket-like frames mounted within said cabinet coaxial with said openings on respective different ones of said left and right walls;
- c) a mass weighing approximately 2 lbs.;
- d) a first circular flexible surround secured at its midpoint to said mass and having its outer periphery secured to said first basket-like frame at said frame's junction with one of said left and right walls;
- e) a speaker cone having a large diameter outer end and a small diameter inner end;
- f) a second circular flexible surround secured to said large diameter end of said speaker cone and extending radially outward from the periphery thereof with the outer peripheral edge of said second surround being secured to said second basket-like frame at said frame's junction with the other of said left and right walls;
- g) means defining an annular magnet weighing approximately 225 oz. fixedly mounted within said cabinet;
- h) a cylindrical pole piece fixedly mounted within said cabinet, said pole piece extending through said annular magnet and being spaced therefrom with said space defining an annular magnetic gap;
- i) a cylindrical voice coil former having an inside diameter slightly greater than the outside diameter of said cylindrical pole piece and extending into said magnetic gap, the outboard end of said cylindrical voice coil former being affixed to said small diameter end of said speaker cone;
- j) a voice coil wound about said voice coil former and positioned thereon so as to be located within said annular magnetic gap in spaced relation to said magnet;
- k) said first and second flexible circular surrounds each having a uniform thickness at least equal to 0.1″ and an edgeroll having a diameter of at least 1.5″ with said edgeroll on said first surround located outboard of said mass and inboard of the outer peripheral edge of said first basket-like frame, and said edgeroll on said second surround located outboard of said large diameter end of said speaker cone and inboard of the outer peripheral end of said second basket-like frame, said first and second flexible surrounds having sufficient strength and rigidity to stand off internal box pressure within said cabinet in the range of from about 1.5 lbs./in2 to about 3 lbs./in2;
- l) a first annular flexible spider secured at its outer periphery to said first basket-like frame and at its inner periphery to said mass;
- m) a second annular flexible spider secured at its outer periphery to said second basket-like frame and at its inner periphery to said voice coil former;
- n) said first surround and said first spider defining the sole suspension means within said cabinet for said mass, and said second surround and said second spider defining the sole suspension means within said cabinet for said voice coil former, voice coil and speaker cone, and being capable of accommodating peak-to-peak coaxial strokes of about 2.5″ for each of: i) said mass; and ii), said voice coil former, voice coil and speaker cone, without significant wobble;
- o) a tracking downconvertor drive amplifier mounted in said cabinet for generating (+)-v and (−)-v audio output signals and alternately delivering said signals to said voice coil, said amplifier characterized by its ability to deliver 2,700 watts rms and to swing 104 volts rms;
- p) said tracking downconvertor drive amplifier including: i) a (+) Tracking Downconvertor Power Supply for generating (+)-v audio signals; ii) a (−) Tracking Downconvertor Power Supply for generating (−)-v audio signals; and iii), a Driver Amplifier coupled to the outputs of said (+) and (−) Tracking Downconvertor Power Supplies for receipt of said (+)-v and (−)-v audio signals and for delivering said signals alternately to said voice coil for establishing an alternating magnetic flux field thereabout;
- q) means including tinsel leads for coupling said voice coil to said Driver Amplifier;
- r) means for maintaining said tinsel leads under tension during reciprocation of said voice coil driven driver through its peak-to-peak stroke of about 2.5″;
- s) means for inputting the left and right channels of audio signal information to be processed to said subwoofer cabinet and for summing the left and right channel audio signal information at different acoustic dB levels so as to produce one of two composite audio signals (L+R)+α(L−R) and α(L+R)+(L−R) where the (L−R) component of the input audio signal representing the stereo sound field is retained;
- t) means for feeding said composite audio signal in parallel to first and second signal processing channels wherein said first signal processing channel includes first and second inverting amplifier means spaced apart by a first opto-coupler and said second signal processing channel includes first and second unity gain buffers spaced apart by a second opto-coupler;
- u) means for summing the twice inverted audio signals output from said second inverting amplifier means in said first signal processing channel with said audio signal output from said second unity gain buffer in said second signal processing channel to produce a composite audio output signal to be processed and wherein said first and second opto-couplers provide breaks which prevent any continuous ground loop between input and output grounds; and, any hum signal generated at said first opto-coupler is inverted by said second inverting amplifier means in said first signal processing channel and summed with any hum signal generated at said second opto-coupler and output from said second unity gain buffer in said second signal processing channel so as to cancel and effectively eliminate any ground loop induced 60 Hz hum signal;
- v) a Diode Steering Network for separating the composite audio signal output from said first and second signal processing channels into its positive-going and negative-going portions and for steering: i) said positive-going portions of said audio signal to said (+) Tracking Downconvertor Power Supply; ii) said negative-going portions of said audio signal to said (−) Tracking Downconvertor Power Supply; and iii), both said positive-going and said negative-going portions of said composite audio signal to said Driver Amplifier for enabling said Driver Amplifier to alternately deliver said (+)-v and (−)-v signals input from said (+) and (−) Tracking Downconvertor Power Supplies to said voice coil; whereby said voice coil former is axially reciprocated within said magnetic gap through a peak-to-peak stroke of about 2.5″ as a result of interaction between the first magnetic flux field generated by said magnet and the second magnetic flux field generated by said voice coil with said voice coil therefore cutting many lines of flux within said interacting magnetic flux fields and thereby generating a large back emf which acts in opposition to the emf applied to said voice coil by said tracking downconvertor drive amplifier and, thereby preventing the flow of damaging stall mode currents in said voice coil and minimizing heat dissipation requirements; and, wherein the force applied to said voice coil driven subwoofer given by Bli is equal and opposite to the force applied to said mass driven subwoofer Mdv/dt, the air contained within said cabinet is alternately: i) pressurized to pressures in the range of from about 1.5 lbs./in2 to about 3 lbs./in2; and ii), rarefied, during inward and outward movement respectively of said voice coil, voice coil former and speaker cone so that said mass driven subwoofer and said voice coil driven subwoofer simultaneously move outward and simultaneously move inward with PUSH/PULL strokes of about 2.5″ and at a frequency determined by the acoustic signal being processed through said tracking downconvertor drive amplifier.
2. A voice coil driven woofer comprising, in combination:
- a) a cabinet having front, rear, left, right, top and bottom walls defining a sealed box enclosing a volume of space of less than 1 ft3 with an opening formed in one of said walls;
- b) a basket-like frame mounted within said cabinet on said one wall coaxial with said opening;
- c) a speaker cone having a large diameter outer end and a small diameter inner end;
- d) a flexible surround secured to said large diameter end of said speaker cone and extending radially outward from the periphery thereof with the outer peripheral edge of said surround being secured to said basket-like frame at said frame's juncture with said wall;
- e) means defining an annular magnet weighing approximately 225 oz. fixedly mounted within said cabinet;
- f) a cylindrical pole piece fixedly mounted within said cabinet, said pole piece extending through said annular magnet and being spaced therefrom with said space defining an annular magnetic gap;
- g) a cylindrical voice coil former having an inside diameter slightly greater than the outside diameter of said pole piece extending into said magnetic gap, the outer end of said cylindrical voice coil former being affixed to said small diameter end of said speaker cone;
- h) a voice coil wound about said voice coil former and positioned thereon so as to be located within said annular magnetic gap in spaced relation to said magnet;
- i) said flexible circular surround having a uniform thickness at least equal to 0.1″ and an edgeroll having a diameter of at least 1.5″ with said edgeroll located outboard of said large diameter end of said speaker cone and inboard of the outer peripheral end of said basket-like frame, said surround having sufficient strength and rigidity to stand off internal box pressures within said cabinet in the range of from about 1.5 lbs./in2 to about 3 lbs./in2;
- j) an annular flexible spider secured at its outer periphery to said basket-like frame and at its inner periphery to said voice coil former;
- k) said surround and said spider defining the sole suspension means within said cabinet for said voice coil former, voice coil and speaker cone and being capable of accommodating peak-to-peak strokes of about 2.5″ for said voice coil former, voice coil and speaker cone without significant wobble;
- 1) a tracking downconvertor drive amplifier mounted in said cabinet for generating (+)-v and (−)-v audio output signals and alternately delivering said signals to said voice coil, said amplifier characterized by its ability to deliver 2,700 watts rms and to swing 104 volts rms;
- m) said tracking downconvertor drive amplifier including: i) a (+) Tracking Downconvertor Power Supply for generating (+)-v audio signals; ii) a (−) Tracking Downconvertor Power Supply for generating (−)-v audio signals; and iii), a Driver Amplifier coupled to the outputs of said (+) and (−) Tracking Downconvertor Power Supplies for receipt of said (+)-v and (−)-v audio signals and for delivering said signals alternately to said voice coil for establishing an alternating magnetic flux field thereabout;
- n) means for inputting a composite audio signal to be processed to said subwoofer;
- o) a Diode Steering Network for separating the composite audio signal input to said subwoofer into its positive-going and negative-going portions and for steering: i) said positive-going portions of said audio signal to said (+) Tracking Downconvertor Power Supply; ii) said negativegoing portions of said audio signal to said (−) Tracking Downconvertor Power Supply; and iii), both said positive-going and said negative-going portions of said composite audio signal to said Driver Amplifier for enabling said Driver Amplifier to alternately deliver said (+)-v and (−)-v audio signals input from said (+) and (−) Tracking Downconvertor Power Supplies to said voice coil;
- whereby said voice coil former is axially reciprocated within said magnetic gap through a peak-to-peak stroke of about 2.5″ as a result of interaction between the magnetic flux field generated by said magnet and the magnetic flux field generated by said voice coil with said voice coil therefore cutting many lines of flux within said interacting magnetic flux fields and thereby generating a large back emf which acts in opposition to the emf applied to said voice coil by said tracking downconvertor drive amplifier so as to prevent flow of damaging stall mode current in said voice coil and thereby minimize heat dissipation requirements; wherein the air contained within said cabinet is pressurized to pressures in the range of from 1.5 lbs./in2 to about 3 lbs./in2 and alternately rarefied so that said voice coil former, voice coil and speaker cone move outwardly and inwardly with PUSH/PULL strokes of about 2.5″ and at a frequency determined by the acoustic signal being processed through said tracking downconvertor drive amplifier.
3. A resilient suspension system for supporting movable driver components within stationary driver components in a driven driver mounted in a subwoofer cabinet, said resilient suspension system comprising, in combination:
- a) an annular flexible spider adapted to be coupled at its inner periphery to the movable components of said driver and at its outer periphery to the stationary components of said driver; and,
- b) a circular surround formed of compressible surround foam, said circular surround having an edgeroll adjacent its outer periphery, said circular surround adapted to be attached to the movable driver components inboard of said edgeroll and to the stationary driver components at the outer periphery of said surround, said surround: i) having a uniform compressed thickness of at least 0.1″; ii) having an edgeroll diameter of at least 1.5″; and iii), being capable of standing off internal box pressures generated within the subwoofer in the range of from about 1.5 lbs./in2 to about 3 lbs./in2.
4. A resilient suspension system as set forth in claim 3 wherein said surround is formed of n laminations of surround foam having an initial aggregate thickness of at least 2{fraction (3/16)}″ compressed to a uniform thickness of at least 0.1″.
5. A resilient suspension system as set forth in claim 4 wherein said n laminations is equal to five laminations, each having an initial thickness of about {fraction (7/16)}″.
6. A resilient suspension system as set forth in claim 4 wherein said n laminations of surround foam have an initial aggregate thickness of at least {fraction (3/16)}″ compressed to a uniform thickness of at least 0.14″.
7. A resilient suspension system as set forth in claim 6 wherein said n laminations is equal to seven laminations, each having an initial thickness of about {fraction (7/16)}″.
8. A flexible, resilient surround for use in suspending the movable driver components of a subwoofer driver from the stationary driver components of a subwoofer driver comprising a circular surround formed of compressible surround foam, said circular surround having an edgeroll adjacent its outer periphery, said circular surround adapted to be attached to the movable driver components inboard of said edgeroll and to the stationary driver components at the outer periphery of said surround, said surround: i) having a uniform compressed thickness of at least 0.1″; ii) having an edgeroll diameter of at least 1.5″; and iii), being capable of standing off internal box pressures generated within the subwoofer in the range of from about 1.5 lbs./in2 to about 3 lbs./in2.
9. A flexible resilient surround as set forth in claim 8 wherein said surround is formed of n laminations of surround foam having an initial thickness of at least 2{fraction (3/16)}″ compressed to a uniform thickness of at least 0.1″.
10. A flexible resilient surround as set forth in claim 9 wherein said n laminations is equal to five laminations, each having an initial thickness of about {fraction (7/16)}″.
11. A flexible resilient surround as set forth in claim 9 wherein said n laminations of surround foam have an initial aggregate thickness of at least 3{fraction (1/16)}″ compressed to a uniform thickness of at least 0.14″.
12. A flexible resilient surround as set forth in claim 11 wherein said n laminations is equal to seven laminations each having an initial thickness of about {fraction (7/16)}″.
13. The method of making a surround capable of standing off internal subwoofer box pressures of from about 1.5 lbs./in2 to about 3 lbs./in2 while stably supporting the subwoofer driver substantially without wobble as it moves through a peak-to-peak stroke of about 2.5″, said method comprising the steps of:
- a) placing cellular surround foam having an aggregate thickness of at least 2{fraction (3/16)}″ intermediate complementary male and female dies; and
- b) closing the male and female dies relative to one another for a period of time T at a pressure P and at a temperature F sufficient to form a surround having a uniform thickness of from about 0.1″ to about 0.14″, and an edgeroll having a diameter of at least 1.5″.
14. The method as set forth in claim 13 wherein the cellular surround foam aggregating at least 2{fraction (3/16)}″ comprises at least five layers of cellular surround foam each approximately {fraction (7/16)}″ thick.
15. The method as set forth in claim 13 wherein T is in the range of 40 to 90 seconds, P is in the range of 60 to 100 psi, and F is in the range of 420° F. to 450° F.
16. The method as set forth in claim 13 wherein T is approximately 45 seconds, P is approximately 80 psi, and F is approximately 430° F.
17. The method as set forth in claim 13 wherein the cellular surround foam aggregates an initial thickness of at least 3{fraction (1/16)}″ and comprises seven layers of cellular surround foam, each approximately {fraction (7/16)}″ thick compressed to a uniform thickness of at least 0.14″.
18. Subwoofer apparatus including circuitry for converting the left and right channels of audio signal information input to a subwoofer into one of two composite audio signals (L+R)+α(L−R) and α(L+R)+(L−R) where the (L−R) components of the audio signal representing the stereo sound field are retained, said subwoofer apparatus comprising, in combination:
- a) left and right channel inputs for the audio signal; and,
- b) means for summing the left channel audio signal input and the right channel audio signal input at different acoustic dB levels so as to deliver one of the two following output composite audio signals: i) (L+R)+α(L−R); and, ii) α((L+R)+(L−R)
- wherein said left and right channel inputs comprise first and second unity gain buffers for respectively receiving and outputting the left and right channel components of the audio signal; and, said means for summing the left channel audio signal input and the right channel audio signal input at different acoustic dB levels constitutes first and second parallel resistors R1 and R2 respectively coupled to the outputs of said first and second unity gain buffers whereby said composite audio output signal is derived from the sum of the left and right channel signal information at the junction of said two resistors and said resistors R1 and R2 have substantially different resistor values.
19. Subwoofer apparatus as set forth in claim 18 wherein one of said resistors R1 and R2 is approximately 680 ohms and the other of said resistors R1 and R2 is approximately 1600 ohms.
20. Subwoofer apparatus including circuitry for eliminating undesirable ground loops and ground loop induced 60 Hz hum from a composite audio signal to be processed, said apparatus comprising, in combination:
- a) means for feeding the composite audio signal in parallel to first and second signal processing channels wherein said first signal processing channel includes first and second inverting amplifier means spaced apart by a first opto-coupler and said second signal processing channel includes first and second unity gain buffers spaced apart by a second opto-coupler; and
- b) means for summing the twice inverted audio signal output from said second inverting amplifier means in said first signal processing channel with said audio signal output from said second unity gain buffer in said second signal processing channel to produce a composite audio output signal to be processed and wherein said first and second opto-couplers provide breaks which prevent any completed ground loop between input and output grounds and any hum signal generated at said first output coupler is inverted by said second inverting amplifier means in said first signal processing channel and summed with a non-inverted hum signal output from said second unity gain buffer in said second signal processing channel so as to cancel and effectively eliminate the ground loop induced 60 Hz hum signal.
21. Subwoofer apparatus of the type including a voice coil driven driver comprising, in combination:
- a) stationary driver components including:
- i) a basket-like frame;
- ii) an annular magnet weighing approximately 225 oz.; and,
- iii) a pole piece extending through said annular magnet and defining a magnetic gap therebetween;
- b) movable driver components including:
- iv) a cylindrical voice coil former adapted to reciprocate in said magnetic gap through a peak-to-peak stroke of about 2.5″;
- v) a voice coil wound about said former and positioned thereon so as to be located within said magnetic gap and spaced from said annular magnet;
- vi) a speaker cone having a large diameter end and a small diameter end wherein said small diameter end is attached to one end of said voice coil former;
- vii) a flexible circular surround having an edgeroll adjacent its outer periphery, said surround being attached to said large diameter end of said speaker cone inboard of said edgeroll and being attached outboard of said edgeroll to said basket-like frame; and,
- viii) an annular flexible spider attached at its inner periphery to said cylindrical voice coil former and at its outer periphery to said basket-like frame;
- c) electrical leads extending from said voice coil to said speaker cone;
- d) tinsel leads coupled to said electrical leads at said speaker cone and extending to said basket-like frame, said tinsel leads adapted to be coupled to the drive amplifier of a subwoofer; and,
- e) means for maintaining said tinsel leads under tension in the span between said speaker cone and said basket-like frame at all positions of said movable driver components; whereby, as said movable driver components move inwardly and outwardly through peak-to-peak strokes of about 2.5″, said tinsel leads are prevented from flapping and striking said speaker cone and, therefore, undesirable noise resulting from said tinsel leads striking said speaker cone during axial reciprocation of said speaker cone is eliminated.
Type: Application
Filed: May 19, 2003
Publication Date: Feb 17, 2005
Inventor: Robert Carver (Snohomish, WA)
Application Number: 10/441,656
