Abstract: A digital/analog conversion apparatus for converting a digital signal into an analog signal. The digital/analog conversion apparatus can generate a high-quality analog signal, even when elements configuring the digital/analog conversion apparatus have variance, with high resolution and a small circuit size. The data conversion apparatus is provided with a first data converter for reducing the number of bits of an input signal, a second data converter for converting the format of the first output signal, and a third data converter for conversion into a code which corresponds to the history of the output from the second data converter.

Abstract: A digital audio driver having a floating PWM input and for controlling a stage of high voltage, high speed high- and low-side MOSFETs series connected at a node. The driver includes a floating input interface circuit having a protection circuit to provide secure protection sequence against over-current conditions; and high and low side circuits for driving the high- and low-side MOSFETs, each high and low side circuit including a bi-directional current sensing circuit which requires no external shunt resistors that enables capture of over-current conditions at either positive or negative load current direction. The RDS(ON) of the high- and low-side MOSFETs is used as current sensing resistors, once the RDS(ON) exceeds a pre-determined threshold, an over current output signal is fed to the protection block to shutdown the MOSFET to protect the devices.

Abstract: A semiconductor device is disclosed. The semiconductor device includes a digital audio circuit which converts an input digital signal into an analog audio signal, a DC-DC converter having a switching power source circuit, and an audible frequency determining circuit. In order that a difference between a frequency of a first clock signal for digital to analog conversion which is used in the digital audio circuit and a frequency of a second clock signal for switching control which is used in a DC-DC converter exceeds a maximum audible frequency, a frequency comparing circuit in the audible frequency determining circuit outputs a signal to a frequency changing circuit in the DC-DC converter. The frequency changing circuit causes a second oscillating circuit to change the second frequency.

Abstract: A dual-coil, dual magnetic gap electromagnetic transducer is provided where each voice coil is wired to include separate leads so that each individual voice coil may be driven by a separate amplifier or by a separate bridged amplifier. Signal processing may further be utilized to increase the output of the loudspeaker, to achieve extreme excursion without extreme distortion and to provide for alternative voice coil designs to address common problems with dual-coil, dual magnetic gap transducers, including, but not limited to, heat generation.

Abstract: An power-saving amplifying device is disclosed, the power-saving amplifying device uses a micro controller unit (MCU) to receive a control signal transmitted by a volume controller and to generate a decision signal based on the control signal; the MCU transmits the decision signal to the volume controlling circuit for obtaining a drive signal, then the volume controlling circuit transmits the drive signal to a power amplifier for driving a speaker to output a sound with a required volume; the MCU also calculates an output value of a PWM signal and transmits the PWM signal to a DC integrating circuit for rectifying and integrating the PWM signal into a DC voltage; the DC voltage is coupled with a voltage control terminal of the power supply to increase or decrease the DC voltage outputted by the power supply to the power amplifier, thereby reducing power consumption by using the volume to control the output voltage of the power supply.

Abstract: The installation size of hearing apparatuses and in particular of hearing devices is to be reduced. Provision is thus made for a hearing apparatus with a transmitting facility including an antenna for the wireless, electromagnetic transmission of data and a switching controller including an inductor, which is used to supply energy to the hearing apparatus and the transmitting facility, with the inductor of the switching controller being identical to the antenna of the transmitting facility. This multiple use of the inductor can save on installation space. In order to avoid mutual interference of the transmitting facility and the switching controller, the signals thereof are modulated independently of one another.

Abstract: A speaker unit performing sound output in proportion to electric current by current driving includes: a frame having an opening; a magnet arranged inside the frame and formed in an annular shape; a yoke including a shaft-shaped insertion arrangement portion which is inserted into a center of the magnet; a coil bobbin formed in a cylindrical shape; a coil wound around an outer peripheral surface of the coil bobbin; a damper having elasticity and connected between the frame and the coil bobbin; a cone connected to the coil bobbin at an inner peripheral portion and fixed to an opening edge of the opening of the frame at an outer peripheral portion, which vibrates with movement of the coil bobbin; and a sound absorbing material arranged inside the coil bobbin.

Abstract: A vibration generator for a portable electronic device includes a speaker driver and a counterweight retained by a housing to form a closed assembly. When a communications transmission is received by the electronic device, an input force signal is transmitted to the speaker driver to apply a force at a frequency substantially below its resonance frequency. Air sealed within the vibration generator between the speaker driver and the counterweight transmits the force signal inputted to the speaker driver to the counterweight with minimal dissipation, thereby causing the counterweight to vibrate at substantially the same frequency as that of the input force signal. The vibrations of the counterweight alert a user that a communications transmission is being received.

Abstract: A drive mechanism @is comprised with a set comprising a plurality of magnetic bodies, means for supplying a frequency signal to said set, and means for producing movement caused by the attraction/repulsion between the magnetic bodies. The movement is the driving source of the drive mechanism.

Abstract: A method of optimizing the low frequency audio response emanating from a pair of low frequency transducers housed within a cabinet. The low frequency transducers are electrically connected to a power amplifier and source of audio content. The resonant frequency (Fs) and amplitude (Q) are characterized as to the high-pass pole of the low frequency transducers as they are mounted within the cabinet. An equalizer is placed between the amplifier and source of audio content for canceling the complex pole of the low frequency transducers and for establishing a new complex pole at a cut off frequency below which the sound generated by the low frequency transducers will diminish.

Abstract: An apparatus for monitoring speaker cone displacement in an audio speaker includes: (a) an electromagnetic coil structure; (b) a ferrous core structure; the ferrous core structure and the electromagnetic coil structure being mounted with the speaker to effect variable electromagnetic coupling between the ferrous core structure and the electromagnetic coil structure as the speaker cone moves; (c) a signal injecting circuit coupled with the electromagnetic coil structure for injecting a predetermined input signal into the electromagnetic coil structure; and (d) a signal monitoring circuit coupled with the electromagnetic coil structure; the signal monitoring circuit receiving an output signal from the electromagnetic coil structure and generating an indicating signal based upon the output signal; at least one signal characteristic of the indicating signal being related with the cone displacement.

Abstract: A speaker driving apparatus includes a speaker enclosure whose inside is tightly closed, at least two speakers that are provided to the speaker enclosure so as to have a common rear space, and a signal supplying unit that supplies a stereo left channel signal to the speaker in a first group and supplies a stereo right channel signal to the speaker in a second group. The at least two speakers being divided into two groups as the first group and the second group.

Abstract: A loudspeaker includes a horn including a first end panel, a second end panel, a first side panel, and a second side panel. Edges of at least the first and second side panels define a diffraction slot opening. The first and second side panels are each fabricated from a sheet of flexible material held in a stressed, curved shape by at least a rigid support member. The panels are designed by an automated process based on a number of electro-acoustic transducers to be used in a loudspeaker, horizontal and vertical coverage angles for the loudspeaker, and a wall length for a horn of the loudspeaker.

Abstract: The present invention utilizes switching power amplifier technology to improve the performance of self-amplified speaker system. In contrast to analog Class A and Class AB amplifiers, the present invention utilizes a digital class D amplifier. Class D amplifiers are a pulse width modulated or digital switching amplifier configuration. The Class D amplifiers of the present invention includes 2-pole compensation feedback and power supply tracking that improves stability and total harmonic distortion over conventional power amplifiers. Class D amplifiers have an average electrical efficiency value of at least 65%. This level of electrical efficiency leads to reduction in the amount of power lost in the device or systems that result in heat generation.

Abstract: A system and method for playing audio material is described. The audio material is illustratively downloaded from a network, or from a storage media, each coupled to a loudspeaker through a speaker drive unit. A speaker authorization signal is provided to the speaker drive unit from the network or storage media. The speaker drive unit provides an audio signal to the loudspeaker if the authorization signal indicates that the loudspeaker is authorized to play the audio material. The speaker drive unit does not provide an audio signal to the loudspeaker if the authorization signal indicates that the loudspeaker is not authorized to play the audio material. The system and method includes a monitoring unit to furnish a signal indicating the sound generated by the loudspeaker, to be stored, and to determine whether the loudspeaker has played the audio material.

Abstract: The disclosed method provides audio location perception to an endpoint in a multipoint videoconference by providing a plurality of audio streams to the endpoint, wherein each of the audio streams corresponds to one of the loudspeakers at the endpoint. The audio streams are differentiated so as to emphasize broadcasting of the audio streams through one or more loudspeakers closest to a position of a speaking endpoint in a videoconference layout that is displayed at the endpoint. For example, the audio broadcast at a loudspeaker that is at a far-side of the screen might be attenuated or time delayed compared to audio broadcast at a loudspeaker that is located at a near-side of the display. The disclosure also provides a multipoint control unit (MCU) that processes audio signals from two or more endpoints according to the positions in a layout of the endpoints and then transmits processed audio streams to the endpoints in a way that allows endpoints to broadcast spatially correlated audio.

Abstract: A loudspeaker provides increased magnetic flux from multiple magnets to drive voice coils to generate sound. The loudspeaker is formed as a smaller profile and reduced weight package. The loudspeaker includes a dual pole, first and second magnets, first and second front plates, and first and second gaps. The polarities of the first and second magnets are aligned in the same direction. The first and second magnets may be disk or ring-shaped and may be coupled to a flange of the dual pole. The first and second gaps may be formed between the inner diameters of the first and second magnets and the dual pole. The magnetic flux produced by the first and second magnets may be combined, directed, and concentrated within the first and second gaps by the dual pole and the front plates. At least portions of a first and a second voice coil may be positioned within the first and second gaps, respectively, and diaphragms may be coupled to the first and second voice coils.

Abstract: A system and method for playing audio material is described. The audio material is illustratively downloaded from a network, or from a storage media, each coupled to a loudspeaker through a speaker drive unit. A speaker authorization signal is provided to the speaker drive unit from the network or storage media. The speaker drive unit provides an audio signal to the loudspeaker if the authorization signal indicates that the loudspeaker is authorized to play the audio material. The speaker drive unit does not provide an audio signal to the loudspeaker if the authorization signal indicates that the loudspeaker is not authorized to play the audio material. The system and method includes a monitoring unit to furnish a signal indicating the sound generated by the loudspeaker, to be stored, and to determine whether the loudspeaker has played the audio material.

Abstract: An amplifier circuit is disclosed having an output transistor for driving a complex load over a drive frequency range, wherein in the lower part of the range an inductive component of the load dominates and in the upper part the inductive component does not dominate. The amplifier circuit includes a current mirror circuit that is connected upstream of the output transistor and has a shunt path to a second potential, for the purpose of relatively reducing a DC current flowing through the output transistor in comparison with an AC current flowing through the latter.

Abstract: A diaphragm for a loudspeaker contains resin, aramid fibers, and an organic silicon compound binding the resin with the aramid fibers. By this structure, high elasticity and high internal loss as characteristics of the aramid fibers are maintained; flexibility in the setting of properties of the diaphragm is thus increased. Accordingly, a diaphragm securing humidity resistance reliability and strength, and having a superior appearance can be provided.

Abstract: In a first aspect the present invention provides a compact high efficiency driver suitable for driving a loudspeaker, such as a miniature loudspeaker for mobile phones or hearing aids. The driver comprising an interface for receiving an input signal, a three-level modulator, and a three-level H-bridge. The interface may be adapted to receive a digital input signal. In a preferred embodiment of the driver the H-bridge is controlled by a correction circuit which is operated by a Return-To-Zero scheme. In a further preferred embodiment the driver comprises a supply voltage step-up circuit for increasing a voltage supplied to the H-bridge. In a second aspect the present invention provides a miniature loudspeaker assembly having a built-in driver. In a third aspect the present invention provides a mobile device with a built-in miniature loudspeaker assembly.

Abstract: An apparatus includes two DC/DC converters including two conversion circuits for converting a power supply voltage to first and second output voltages, respectively, two driving circuits for driving the respective conversion circuit based on first and second pulse wave modulated signals, and two pulse width modulation circuits for performing pulse width modulation on a thinned wave signal formed from a first wave signal and on a second wave signal to generate the pulse wave modulated signals, respectively. One DC/DC converter includes a thinning circuit for removing portions of a first wave signal to form the thinned wave signal. The apparatus includes a speaker for generating sound by inputting a signal based on the voltages.

Abstract: A PWM signal generator is operable to generate a first pulse signal and a second pulse signal at least one of before and after generating the first pulse signal. A duty ratio of the second pulse signal is gradually changed. A low-pass filter is operable to convert the first pulse signal output from the PWM signal generator into an analog acoustic signal. The low-pass filter is operable to convert the second pulse signal output from the PWM signal generator into the analog acoustic signal having an inaudible frequency.

Abstract: A piezo-electric speaker ensures a uniform sound in a broad band and can easily reproduce a signal of large amplitude or sound. A piezo-electric speaker has a piezo-electric member to generate a vibration according to an electric signal applied thereto. A piezo-electric vibration plate converts the vibration to a sound. The piezo-electric vibration plate is positioned closely to the piezo-electric member. The piezo-electric vibration plate is divided into parts of any configuration and is connected to the piezo-electric member.

Abstract: A loudspeaker module in the form of a ribbon element, where the module can be equipped with a membrane, 50 millimeters in width or narrower, and with any length from 50 millimeters to 2500 millimeters. The magnet system is equipped with so called booster-magnets in order to reduce loss of magnetic flow in the soft iron pole pieces and in order to equalize and in order to even the magnetic flow at the magnet ends. The signal-feed is designed in the form of passive current-feeding, whereby the inductance's negative impact of the frequency response up to the 1/f point is eliminated. Above the 1/f point, the ribbon membrane is compensation fed from a separate circuit consisting of R and C, whose values have been chosen in such a way that the resulting frequency response is flat over the whole operating area.

Abstract: Each of a plurality of speaklets (MEMS membranes) produces a stream of clicks (discrete pulses of acoustic energy) that are summed to generate the desired soundwave. The speaklets are selected to be energized based on the value of a digital signal. The greater the significance of the bit of the digital signal, the more speaklets that are energized in response to that bit. Thus, a time-varying sound level is generated by time-varying the number of speaklets emitting clicks. Louder sound is generated by increasing the number of speaklets emitting clicks. The present invention represents a substantial advance over the prior art in that sound is generated directly from a digital signal without the need to convert the digital signal first to an analog signal for driving a diaphragm.

Abstract: A method of reproducing audio sound using low level electromagnetism applied to ambient air particles to create a new magnetic field. The method uses a device having at least one winding of electric wires that re wound onto a flexible polymer support. The impedance of the winding is 8 Ohms. The device is connected to an electric audio signal of an acoustic chamber or an acoustic supply. The device and method are useable with audio and audio-video systems, as well as other known methods of communication.

Abstract: In an electromagnetic induction type speaker apparatus, individual constants are set in such a manner that the following formula is satisfied N×(R1×R2)1/2/{2 ?×L1×(1?k2)1/2}?20000 where R1 is the DC resistance of a primary coil 15: L1 is the inductance of the primary coil 15; N is the number of turns of the primary coil 15; R2 is the DC resistance of the secondary coil 18; L2 is the inductance of the secondary coil 18; and k is the coupling coefficient of the primary coil 15 and the secondary coil 18. In addition, the constants L1 and L2 are selected in such a manner that the ratio of the inductance L1 and the inductance L2 becomes equal to in the ratio of the DC resistance R1 and the DC resistance R2.

Abstract: A magnetostrictive actuator comprises a rod of giant magnetostrictive material, biasing permanent magnets arranged at each end thereof and coaxially therewith so as to pass a magnetic field through the rod. An energizing electromagnetic coil is connected to an energizer so as to superimpose on the magnetic field passing through the rod an alternating magnetic field to cause variation in the length of the rod in response thereto. The permanent magnets are each in the form of a disc having a cross-sectional area substantially greater than that of the rod and are spaced from the ends of the rods by material of low magnetic permeability. The magnetic field in the rod is thereby substantially linear along the length thereof.

Abstract: A speaker system utilizes an isolation transformer with an independent secondary coil to produce power for a poll back response circuit.

Abstract: The present invention relates to an electro dynamic speaker unit comprising an electro dynamic motor adapted for receiving a first electrical signal and to drive a diaphragm in accordance with the received first electrical signal. The speaker unit further comprises sensing means adapted for generating a second electrical signal in accordance with a movement of the diaphragm, and determining means adapted for receiving the first and the second electrical signals so as to determine an acoustical load of the speaker unit from the first and the second electrical signals. The determining means further generates a third electrical signal in accordance with the determined acoustical load of the speaker unit. The present invention further relates to a method for active leak compensation of an electro dynamic speaker unit.

Abstract: The present invention relates to an apparatus for converting an audio signal from a source (25) into audio waves, comprising a modulator (17), for modulating said audio signal, an amplifying switching stage (15), for amplifying a modulated audio signal supplied from the modulator, and a transducer (19). The transducer is connected directly to the switching stage, and is arranged to convert a pulse train from the switching stage into audio waves. Further, the modulator, the switching stage and the conversion means are integrated mechanically and electrically in one operational unit, being connectable directly to a mains power supply (12). By this electrical integration, no separate filtering is required, but instead the inherent qualities of the transducer are used for accomplishing filtering of the pulse train.

Abstract: Apparatus for use with a loud speaker with a volume control function, the apparatus having a recess for releasably receiving an audio device, a first connector on the apparatus for electrical connection with a second connector of the audio device to enable functional connectivity between the apparatus and the audio device, the apparatus including: (a) a volume control for controlling the volume of the loud speaker, (b) an electrical power connector for supplying electric power to the audio device, and (c) at least one functional connection for functional connection with the audio device for establishing a functional relationship between the first control means and the audio device, the recess being sized and shaped to receive therein the audio device, the recess being of dimensions such that the audio device does not extend beyond edges of the recess when the audio device is functionally engaged in the recess and the first connector and the second connector are engaged.

Abstract: A sound generator circuit configured for a handheld computer is disclosed. A method of producing a tone with a sound generator and handheld computer is also disclosed. The sound generator circuit includes a low pass filter having an input and an output. The input is coupled to a pulse width modulated (PWM) signal line. The sound generator circuit also includes a switching circuit coupled to the output of the low pass filter and being controlled by the output of the low pass filter. Further, the sound generator circuit includes a sound generator having a first and a second terminal. Further still, the sound generator circuit can include a high-pass filter coupled across the first and second terminals.

Abstract: A multifunction acoustic device has a rotor rotatably supported in a frame, a stator provided in the frame. A permanent magnet is provided on the rotor, a coil is provided for forming magnetic fluxes between the rotor and the stator. Voltage detecting means is provided for detecting a voltage generating at the coil. A voltage detected by the voltage detecting means in the operation of the acoustic device is compared with a reference voltage which corresponds to a voltage generating at abnormal rotation of the rotor and for producing an abnormal signal when the detected voltage is equal or higher than the reference voltage. In response to the abnormal signal, the rotor is rotated from a low speed.

Abstract: A driver control circuit (10) that enhances a steep crossover slope while permitting selective shaping or adjusting of its in-band frequency response with a minimum number of components. The driver control circuit includes a signal connector (16) for connecting with a source of audio signals (12); a speaker connector (18) for connecting with a speaker (14); and a frequency passing circuit (20) coupled between the signal connector (16) and the speaker connector (18) for passing a selected range of frequencies of the audio signals to the speaker (14) and for attenuating other frequencies. The frequency passing circuit (20) includes components forming a traditional low-pass or high-pass filter network and a resistive component (R1) connected in parallel across the second series mounted component of the low-pass or high-pass filter network.

Abstract: An acoustic drive circuit for driving a headphone for converting variation of magnetic force, occurring to a voice coil, in sound, and outputting the sound, comprises a power amplifier for amplifying a signal at a frequency within the speech band, and outputting the signal after amplification, at a voltage with a given bias voltage superposed thereon, to one end of the voice coil of the headphone, and a pulse generation circuit for generating a pulse signal at a frequency higher than those in the speech band, having an average voltage equivalent to the bias voltage, and for outputting the pulse signal to the other end of the voice coil. The pulse generation circuit generates rectangular waves at a frequency higher than those in the speech band, having a duty ratio such that the average voltage is equivalent to the bias voltage.

Abstract: A member for producing an audible sound in a vehicle including a speaker area having an upper surface and a lower surface, the speaker area being located on the member. A piezo bimorph is attached to the speaker area, the piezo bimorph including a first piezoelectric element attached to the upper surface of the speaker area, and a second piezoelectric element attached to the lower surface of the speaker area. An amplifier in electrical communication with the piezo bimorph, the amplifier supplying an electrical field to the piezo bimorph, the piezo bimorph causing the speaker area and the member to vibrate, causing an audible sound.

Abstract: A broadband transducer controlled by magnetic field coupling, the transducer has signal volume control of a hi-fi set that is achieved by means of variable resistance originally achieved instead by means of a magnetic field coupler, wherein, the magnetic field coupler has a primary coil and a secondary coil with an adjustable gap therebetween, an adjusting rod is provided in the gap for adjustment and control; thereby, magnetic resistance is controlled for controlling volume of sounds; using of low voltage amplifying saves energy source and lowers cost of production, and makes an amplifier have an ideal acoustic effect able to give sweet sounds such as is done with a vacuum tube type hi-fi set and to give pushout power such as is done with a transistor type hi-fi set.

Abstract: In a first aspect the present invention provides a compact high efficiency driver suitable for driving a loudspeaker, such as a miniature loudspeaker for mobile phones or hearing aids. The driver comprising an interface for receiving an input signal, a three-level modulator, and a three-level H-bridge. The interface may be adapted to receive a digital input signal. In a preferred embodiment of the driver the H-bridge is controlled by a correction circuit which is operated by a Return-To-Zero scheme. In a further preferred embodiment the driver comprises a supply voltage step-up circuit for increasing a voltage supplied to the H-bridge. In a second aspect the present invention provides a miniature loudspeaker assembly having a built-in driver. In a third aspect the present invention provides a mobile device with a built-in miniature loudspeaker assembly.

Abstract: A method and system for using an audio transducer as both an input device and an output device is disclosed. The method and system include digitally modulating a primary input signal for driving the transducer as an output device, sampling an output signal generated from the transducer during off times of the modulated signal, and determining an input signal from the sampled output signal.

Abstract: A woofer that is capable of producing a flashing light show depending upon the volume and frequency of the sounds emitted thereby. The woofer includes at least one light emitting diode and a control circuit that are conveniently mounted on a printed circuit board at the center of the woofer at an inconspicuous location below a transparent dust cover so as to achieve a compact configuration without effecting the aesthetic appearance of the woofer. The woofer also includes a magnetic structure having at least one permanent magnet and at least one electromagnetic voice coil that is adapted to move in first and opposite directions towards and away from the permanent magnet depending upon the changing polarities of an alternating current that is supplied to the electromagnetic voice coil.

Abstract: A system for distributing a source voltage from a signal source to a number of drivers or loudspeakers is disclosed. The system includes at least one autotransformer for connection to the signal source, and a number of drivers electrically connected to the autotransformer. The autotransformers distribute the source voltage across each of the drivers. The autotransformers produce an output voltage across each of the drivers, such that the sum of the output voltages is substantially equal to the source voltage multiplied by the number of drivers.

Abstract: Each of a plurality of speaklets (MEMS membranes) produces a stream of clicks (discrete pulses of acoustic energy) that are summed to generate the desired soundwave. The speaklets are selected to be energized based on the value of a digital signal. The greater the significance of the bit of the digital signal, the more speaklets that are energized in response to that bit. Thus, a time-varying sound level is generated by time-varying the number of speaklets emitting clicks. Louder sound is generated by increasing the number of speaklets emitting clicks. The present invention represents a substantial advance over the prior art in that sound is generated directly from a digital signal without the need to convert the digital signal first to an analog signal for driving a diaphragm.

Abstract: A woofer that is capable of producing a flashing light show depending upon the volume and frequency of the sounds emitted thereby. The woofer includes at least one light emitting diode and a control circuit that are conveniently mounted on a printed circuit board at the center of the woofer at an inconspicuous location below a transparent dust cover so as to achieve a compact configuration without effecting the aesthetic appearance of the woofer. The woofer also includes a magnetic structure having at least one permanent magnet and at least one electromagnetic voice coil that is adapted to move in first and opposite directions towards and away from the permanent magnet depending upon the changing polarities of an alternating current that is supplied to the electromagnetic voice coil.

Abstract: A signal processing system in which a differentially quantized digital signal is used, the digital signal having two bits which represent only three values, of which one value (10 or 01) is zero and the other two (11 and 00) values represent a positive value and a negative value respectively.

Abstract: A sub woofer system is constituted of a real time digital signal processing part 5 that includes an A/D converter 5a, a low pass filter block 5b, a delay block 5c, and a D/A converter block 5d, an analog power amplifier 6 and a speaker 7. The length of delay time of the delay block 5c is set so that the length of group delay time of the digital signal processing part 5 may equal an integral multiple of the length of time corresponding to one wavelength of the crossover point frequency between the digital signal processing part 5 and a main speaker 4. The signal processing is performed under the conditions that have been set as such. In this case, a construction is made up wherein the length of a group delay time produced in the digital type real time digital signal processing part can be set to a given value. By this construction, it is possible to provide a sub woofer system which can improve the phase interference between the main speaker and the sub woofer system at the crossover point between the two.

Abstract: A multifunction acoustic device has a rotor rotatably supported in a frame, a stator provided in the frame. A permanent magnet is provided on the rotor, a coil is provided for forming magnetic fluxes between the rotor and the stator. Voltage detecting means is provided for detecting a voltage generating at the coil. A voltage detected by the voltage detecting means in the operation of the acoustic device is compared with a reference voltage which corresponds to a voltage generating at abnormal rotation of the rotor and for producing an abnormal signal when the detected voltage is equal or higher than the reference voltage. In response to the abnormal signal, the rotor is rotated from a low speed.

Abstract: According to the invention, this magnetic circuit, of known type with a central magnet, is such that the diameter of said central magnet 8.1 is greater than that of the core 9.1, such that said magnet 8.1 has a peripheral projection 14, which is annular and radial, with respect to the core 9.1. The performance of said magnet is thus improved.

Abstract: An ultra-directional speaker system has a speech generation means, an ultrasonic generation means, an amplitude modulation means to which the speech generation means and ultrasonic generation means are connected, an electro-acoustic transducer means which converts an ultrasonic modulated signal that is output from the amplitude modulation means to an acoustic signal, and a virtual sound source positioning means that establishes the position of a virtual sound source by detecting the position of a listener by detecting the ultrasonic waves that are output from the electro-acoustic transducer means and reflected from the listener.