Abstract: The present invention is directed to methods and apparatus for dissipating heat in a voice coil of a loudspeaker, where at least one of: a bobbin having a substantially cylindrical shaped wall member is operable to support the voice coil, and the wall member includes at least one aperture operable to provide thermal communication from the voice coil through the wall member; and a heatsink is coupled to an outer surface of a bobbin and is in thermal communication with the voice coil.

Abstract: A speaker device and associated method for producing a speaker device that includes a voice coil and a radiant layer made of a radiant energy emissive material provided on a surface of the voice coil for suppressing the heat generated at the voice coil while simultaneously improving the input durability of the speaker device.

Abstract: A pole piece 19 of a speaker main unit 1 has a pole 19a engaged with a bobbin 14 from the back side of a diaphragm 12, and a flange 19b horizontally expanding from the base of the pole 19a. In the pole 19a is formed a through hole 19c passing therethrough in an axial direction thereof, and in the bottom end of the through hole 19c is provided with a taper 19d which widens with it goes downward. A thin film piezoelectric element 4 is provided such that the element covers an external opening 19e of the through hole 19c, and one end 4a of a thin film piezoelectric element 4 is adhered to the bottom surface of the flange 19b.

Abstract: A combination voice coil and diaphragm device for use in a receiver is disclosed having a diaphragm injection-molded from plastics, and a voice coil formed integral with the diaphragm by means of thin film plating. The voice coil has electrodes integral with the diaphragm and extended to the periphery of the diaphragm for quick installation in the receiver.

Abstract: It is one object for the present invention to improve current-carrying capacity of a wire and input characteristics. A speaker is provided with a wire unit, which is formed by combining a plurality of unit electric wires and the unit electric wires are electrically parallel with each other to form one voice coil; an insulation member for insulating the unit electric wires each other; a bobbin for being wound by the electric wires; a vibration plate for being vibrated by the bobbin; a magnet for surrounding the bobbin; a yoke for being substantially connected to the magnet; a plate for being substantially connected to the magnet; and a damper for being connected to the bobbin.

Abstract: A knockdown speaker. The speaker includes a magnetic circuit base, a casing, and a vibration unit. The magnetic circuit base is substantially a hollow body having a central projecting cylinder and fixing holes in its top rim. The vibration unit is composed of a funnel-shaped cone socket and a damper set, which are formed by combining a bottom end and a top end of the vibration unit respectively with a sound ring set or a piece of drum paper. The magnetic circuit base is mounted on the bottom rim of the casing. The vibration unit is jointed with the magnetic circuit base via the sound ring set arranged at the bottom end of the vibration unit to form a consolidated knockdown speaker.

Abstract: An inertial vibration transducer for exciting bending waves in a sound-radiating member has a motor coil assembly with a tubular member adapted to be rigidly mounted directly to the sound-radiating member by adhesive means. The transducer has a magnet assembly supported on a resilient suspension, and the magnet of the magnet assembly may be disposed within the tubular member of the motor coil assembly. Loudspeakers incorporating such transducers also are disclosed.

Abstract: In a fixing disk for connecting voice coil with drum paper and retaining them in a speaker, a circular fixed lid for jointing with an upper edge of a voice coil is laid in center of the fixing disk, and the circumferential edge of the fixed lid is connected with a plurality of connection ribs. The other end of each connection rib is then connected with an annular fixed piece, which is inclined in a same oblique angle with the drum paper such that it can be thoroughly fitted on the drum paper when the fixed lid covers the voice coil. By so doing, the fixing disk of this invention can fasten the voice coil and the drum paper together to raise the tone quality of the synchronous vertical vibration of the drum paper and the voice coil when the voice coil is outputting the audio power.

Abstract: An improved structure for the sound coil of loudspeaker comprises a cylinder provided with multiple layers of coils surrounding one end thereon. The coils are divided into sections in the middle position which provide more than two conducting wires. The cylinder is rolled by a single plate and is provided with four layers of coils. The conducting wire extends to the other end of cylinder and is wrapped with oilpaper; and connects to a piece of thick wire. The cylinder is provided with several ventilation holes. Every two layers of coil being a independent wire material, the sound coil comprised four conducting wires; or each layer of coil being a independent wire material, the sound coil comprised eight conducting wires. Thus the sound coil produces larger output power and reduces the size of sound coil, the coils surrounding the cylinder, production costs, and the size of products.

Abstract: A loudspeaker has a diaphragm with a voice coil disposed about its perimeter and extending in a gap into which the flux of an annular rare earth magnet is focused. An opening behind the diaphragm communicates through the speaker frame. The voice coil may have two or more windings that are connected in parallel, and may, e.g., be layered on top of one another, so that the impedance of the coil, as well as its depth in the front/back direction of motion, are low. The voice coil is preferably implemented using a polyimide form or bobbin, which has patterned lead-in conductors embedded therein to bring power to wire windings on the perimeter of the coil. The lead-in conductors extend to, or through, the central opening of a ring magnet, providing a robust ribbon input connection. The ribbon lead-in may be symmetrical, and the central opening further provides an air channel that couples to an auxiliary chamber for enhanced sound.

Abstract: A loudspeaker having a flux gap defined by central pole and a magnet surrounding the central pole, includes a plurality of low-friction ridges extending from an outer surface of a the central pole. A voice coil, connected to the loudspeaker's diaphragm, is free to reciprocate within the flux gap. The ridges are linear and run generally in an axial direction, along a length of the pole where the voice coil reciprocates. Instead of rubbing directly against a metal pole, which has relatively high friction, the voice coil will rub against the ridges, thus reducing some of the noise that would otherwise occur due to rubbing. The voice coil includes a relatively stiff structure, created in part with a ceramic or epoxy material, that is coupled to a diaphragm, and a relatively flexible multiple layer structure at the terminating free end having dampening properties.

Abstract: A speaker includes a diaphragm having a central aperture at which a bobbin with a voice coil wound therearound is mounted, and mounted at the outer periphery thereof on a frame with an edge therebetween, and a magnetic circuit section that has a magnetic gap in which the bobbin is placed, and that drives the diaphragm to vibrate in the frontward and rearward direction. The speaker can use a larger diaphragm by providing the frame with an edge-mounting portion on which the edge is mounted, and a portion formed in front of the edge-mounting portion.

Abstract: A voice coil bobbin comprises a cloth material woven from longitudinal and lateral fibers, and transmits driving force caused by a voice coil wound thereon to a diaphragm. The longitudinal or lateral fibers are obliquely oriented with respect to the direction of the driving force. Thus, rigidity and mechanical strength required for the voice coil bobbin are ensured with reduced weight and cost.

Abstract: A speaker includes: a frame; a magnetic circuit fixed to the frame; a diaphragm fixed to the frame so as to be capable of vibrating in a predetermined direction; a driving force transmitting member connected to the diaphragm; and a damper for supporting the driving force transmitting member, wherein the magnetic circuit is positioned between a first plane and a second plane, the first plane being parallel to the diaphragm and defined as a plane with which at least a portion of the magnetic circuit is in contact, and the second plane being parallel to the diaphragm and defined as a plane with which at least a portion of the magnetic circuit is in contact, and one end of the damper is connected at a position between the first and second planes, and the other end of the damper is connected at another position between the first and second planes.

Abstract: An electroacoustic transducer (1) includes a base (24) and magnetic core (22) a diaphragm (20) supported with a gap between the diaphragm and a forward end of the magnetic core, a magnet (25) constituting a magnetic circuit together with the base (24), the magnetic core (22) and the diaphragm (20) a coil (23) disposed around the magnetic core a coil bobbin (30) for holding the coil (23), a housing (10) for receiving the above-mentioned members, a filler (19) applied to an external surface side of the base (24), and lead terminals (41 and 42) for supplying an electric current. The lead terminals (41 and 42) have protrusion portions (41a and 42a, protruding into an internal surface side of the base (24) in the axial direction of the coil. A coil wire (23a) is wound around the protrusion portions (41a and 42a) so as to be connected to the lead terminals (41 and 42).

Abstract: A linearly compliant, flexible, resilient and flat speaker damper connected between the frame and the cone of the speaker with electrically conductive paths applied to the damper to conduct the signal to be applied to the voice coil of the speaker. A method for linearly compliant audio speaker damping and a method for application of voice coil conductors on the damper.

Abstract: The surrounding structure of the loudspeaker forms an annular structure, including attaching parts and curved part. The cross section of the curved part is in a hollow and approximately elliptical form. The height along the major axis of the ellipse is made parallel to the center axis of the vibrating diaphragm of the loudspeaker while the width along the major axis of the ellipse is set in the direction orthogonal to the center axis of the vibrating diaphragm. In the elliptical surrounding structure having such a structure, the width in the cross section of the surrounding structure of the loudspeaker can be made narrow in comparison with a semi-circular surround, whereby the linearity of the amplitude and the maximum displacement are increased.

Abstract: An electricity-to-sound transducer has a diaphragm having an asymmetric shape which is flat when viewed from a direction of vibration, with major and minor axes, having continuous curvatures of concavity and convexity in a direction of sound irradiation, provided with a slot formed almost at a center of the diaphragm in a direction perpendicular to a longitudinal direction of the diaphragm. An edge portion is formed as surrounding an outer periphery of the diaphragm, an inner section of the edge portion being connected to the outer periphery, the edge portion sustaining the diaphragm so that it can vibrate. A voice coil bobbin has a winding portion around which a voice coil is wound split into two portions in the longitudinal direction of the diaphragm, the bobbin being attached to a rear surface of the diaphragm while the two portions are joined to each other, the joined portions forming a reinforcing beam that reaches a rear surface of a bottom of the slot of the diaphragm.

Abstract: A pole piece 31 is placed on a lower case 21. A pole piece 31 has a core 32 and a base 33. The bobbin portion 24 extends from the lower case 21 toward the internal space of a case 1 so as to surround the outer periphery of the core 32. The bobbin portion 24 is divided into a plurality of portions along the circumferential direction of the core 32. The bobbin portion 24 has basal parts 26 and elongated parts 27. The pole piece 31 is pressed from the above of the lower case 21 in a state where the bobbin portion 24 is passed through holes 35 of the base 33, to be positioned on the outer periphery of the core 32, so that the pole piece is fitted and placed into the lower case 21. A coil 41 is configured by winding a conductor wire 42 around the elongated parts 27 of the bobbin portion 24.

Abstract: A loudspeaker has a diaphragm with a voice coil disposed about its perimeter and extending in a gap into which the flux of an annular rare earth magnet is focused. An opening behind the diaphragm communicates through the speaker frame. The voice coil may have two or more windings that are connected in parallel, and may, e.g., be layered on top of one another, so that the impedance of the coil, as well as its depth in the front/back direction of motion, are low. The voice coil is preferably implemented using a polyimide form or bobbin, which has patterned lead-in conductors embedded therein to bring power to wire windings on the perimeter of the coil. The lead-in conductors extend to, or through, the central opening of a ring magnet, providing a robust ribbon input connection. The ribbon lead-in may be symmetrical, and the central opening further provides an air channel that couples to an auxiliary chamber for enhanced sound.

Abstract: A high efficiency loudspeaker without a damper is provided. The loudspeaker includes magnetic circuit 9 having magnetic gap 14 and voice coil member 15, which has movable coil 16, disposed in magnetic gap 14 of magnetic circuit 9. The loudspeaker also includes diaphragm 17, whose inner peripheral part is linked with voice coil member 15, outside magnetic gap 14 and frame 19 linked with an outer peripheral part of diaphragm 17 via first edge 18. An inner peripheral part of suspension holder 20 is linked with voice coil member 15 at a linked position, which is nearer to magnetic circuit 9 than a linked position of diaphragm 17 and voice coil member 15. An outer peripheral part of suspension holder 20 is linked with frame 19 via second edge 21. First edge 18 and second edge 21 are substantially symmetrical analog each other about a median of first edge 18 and second edge 21.

Abstract: Fixing of a voice coil (16) to a diaphragm (12) is performed by caulk-fixing a coil supporting member (26) to the diaphragm (12) and by fit-supporting the voice coil (16) by the coil supporting member (26). Hereby, the voice coil 16 is physically fixed to the diaphragm (12) and its fixing strength is heightened. The caulk-fixing is performed by subjecting a caulking projection of the coil supporting member (26) to a plastic deformation thereby to provide a caulk-fixed portion (26b), whereby deformation injurious to the acoustic property does not occur in the diaphragm (12). Further, the fit-supporting is performed by interposing a flange portion (16a1) formed at an upper end portion (16a) of the voice coil (16) between an engaging portion (26a) of the coil supporting member (26) and a central flat portion (12b) of the diaphragm (12) and holding it by them from upper and lower sides.

Abstract: The invention relates to a speaker that can cool a voice coil efficiently. A bobbin that supports the voice coil is made from a material having good thermal transfer characteristics. Slits are formed in the bobbin to further promote heat emission from the voice coil.

Abstract: An electroacoustic transducer operating in accordance with the electrodynamic principle include a diaphragm which has in the region of the coil an annular protrusion which is integrally connected to the diaphragm, wherein the coil is attached, preferably glued, to the annular protrusion at a desired distance from the diaphragm. The attachment can be end face against end face. The diaphragm may in the area of the coil have an annular reinforcing corrugation which is attached to the coil in an appropriate manner, preferably by gluing.

Abstract: In a speaker which is constructed in a manner that a voice coil bobbin is attached to an inner circumferential portion of a cone type diaphragm while a voice coil is wound around the voice coil bobbin, and the voice coil is inserted into a magnetic gap, the voice coil bobbin is formed of a conductive material and is provided with a gap extending a lengthwise direction so as to form a one-turn voice coil, and the voice coil is fixed to the voice coil bobbin by a soft bonding agent while a very high frequency audio signal is supplied to the one-turn voice coil forming the voice coil bobbin.

Abstract: A plurality of heat conduction bodies comprising a metallic material are located with a space held between each other, and attached with a connection with at least one of a voice coil bobbin comprising an insulating material and a voice coil. Further, one end of each heat conduction body is connected to a center cap comprising a metallic material. When the voice coil generates heat, the heat can be radiated by transmitting it to the center cap through the heat conduction body. Additionally, the heat conduction body with a shape of band is attached with a space held between each other, and the voice coil bobbin is formed with an insulating material, so that an eddy current caused by a magnetic field in a magnetic gap can be restrained from occurring.

Abstract: An open-type magnetic circuitry of loudspeaker includes a lower yoke having a central portion upward projected to form a bobbin, a magnet positioned on top of the bobbin, a voice coil wound around the bobbin and the magnet, and a diaphragm connected at a root portion to the voice coil. The magnetic circuitry of loudspeaker is characterized in that the lower yoke is provided at an upper side surrounding the bobbin with a plurality of radially equally spaced supporting posts, a top end of which being higher than at least a bottom side of the magnet, and that a ring-shaped upper yoke having a central hole is covered onto the top end of the supporting posts, such that heat produced by the voice coil during working could quickly dissipate via the spaces among the supporting posts. Since no heat would accumulate in the loudspeaker, the loudspeaker could always maintain good sound quality.

Abstract: In a speaker which is constructed in a manner that a voice coil bobbin is attached to an inner circumferential portion of a cone type diaphragm while a voice coil is wound around the voice coil bobbin, and the voice coil is inserted into a magnetic gap, the voice coil bobbin is formed of a conductive material while the voice coil being fixed is the voice coil bobbin by a soft bonding agent, and in a very high range, the voice coil is operated as a driving coil while the voice coil bobbin is operated as a short coil.

Abstract: A speaker 300 is formed using a plate such as a mobile phone display window 310 as a vibrating element. At least two dynamic actuators 950 are positioned behind the edges of the window 310 to actuate the window 310 through its boundary region so as to leave a large uniform area behind the vibrating element for containing any components, e.g. a display or battery.

Abstract: An audio transducer having simple and single means to micro adjust the air gap between the driving element and the driven element.

Abstract: A voice coil bobbin 1 is formed from a material combining a fiber-type material and a ceramic-type-coating agent including metal alkoxide, metal hydroxide, and a colloidal or fine-particulate inorganic substance. The combining process for the ceramic-type-coating agent is performed before or after the fiber-type material is formed into a shape of the voice coil bobbin 1.

Abstract: A loudspeaker assembly includes a chassis, a magnet assembly supported by the chassis and disposed at a rear side thereof, a moveable voice coil, a rear suspension, and a diaphragm connected to the voice coil and to the chassis. The assembly defines a voice coil gap receiving the voice coil. To improve the cooling of the assembly, particularly when the magnet assembly includes neodymium, the assembly is positioned at least substantially in front of the diaphragm, and the chassis is positioned outwardly of the magnet assembly. Heat generated by the coil, which could adversely affect the magnet, is dissipated by conduction to the chassis and by convection and radiation to ambient air. The rear suspension supports the voice coil, is secured to the assembly and is connected to the chassis only through the magnet assembly and through the diaphragm.

Abstract: A speaker having a voice coil bobbin wound around with the voice coil and a detection coil together. The detection coil is formed by a wire whose diameter is smaller than one fourth of that of the wire used for the voice coil, and wound in a space among the voice coil wires. In another example, the voice coil and the detection coil are formed using a flat type wire. In a speaker made in accordance with the present invention, the outer diameter of the whole coil structure containing a voice coil and a detection coil does not increase; as a result, decrement of the magnetic flux density in magnetic gap does not occur. Thus, the signals that proportionately represent the speaker vibration are made available without inviting deterioration in the efficiency of a speaker, nor an increased Q0.

Abstract: A pole piece 31 is placed on a lower case 21. A pole piece 31 has a core 32 and a base 33. The bobbin portion 24 extends from the lower case 21 toward the internal space of a case 1 so as to surround the outer periphery of the core 32. The bobbin portion 24 is divided into a plurality of portions along the circumferential direction of the core 32. The bobbin portion 24 has basal parts 26 and elongated parts 27. The pole piece 31 is pressed from the above of the lower case 21 in a state where the bobbin portion 24 is passed through holes 35 of the base 33, to be positioned on the outer periphery of the core 32, so that the pole piece is fitted and placed into the lower case 21. A coil 41 is configured by winding a conductor wire 42 around the elongated parts 27 of the bobbin portion 24.

Abstract: The invention relates to a speaker that can cool a voice coil efficiently. A bobbin that supports the voice coil is made from a material having good thermal transfer characteristics. Slits are formed in the bobbin to further promote heat emission from the voice coil.

Abstract: A speaker apparatus, in which sound wave is uniformly radiated to front and rear sides thereof, to prevent distortion of sound due to one way vibration. The speaker apparatus includes a bobbin to vibrate a vibrating plate according to a current applied to a voice coil, and a yoke is disposed at an inner side of the bobbin and spaced apart from the bobbin by a predetermined interval. A sound wave guiding member is disposed at an inner side of the yoke so as to guide the sound wave to the front side and the rear side of the speaker apparatus.

Abstract: An electricity-to-sound transducer has a diaphragm having an asymmetric shape which is flat when viewed from a direction of vibration, with major and minor axes, having continuous curvatures of concavity and convexity in a direction of sound irradiation, provided with a slot formed almost at a center of the diaphragm in a direction perpendicular to a longitudinal direction of the diaphragm. An edge portion is formed as surrounding an outer periphery of the diaphragm, an inner section of the edge portion being connected to the outer periphery, the edge portion sustaining the diaphragm so that it can vibrate. A voice coil bobbin has a winding portion around which a voice coil is wound split into two portions in the longitudinal direction of the diaphragm, the bobbin being attached to a rear surface of the diaphragm while the two portions are joined to each other, the joined portions forming a reinforcing beam that reaches a rear surface of a bottom of the slot of the diaphragm.

Abstract: A speaker apparatus includes a frame having a magnetic circuit, a voice coil bobbin installed in the frame to be magnetically coupled to the magnetic circuit, and a diaphragm movably installed in the frame and fixed to the voice coil bobbin so as to be driven by activating the magnetic circuit. The diaphragm has a positioning portion that had been used for securing the diaphragm relative to the magnetic circuit during an installation of the diaphragm in the frame.

Abstract: A speaker comprising a magnetic circuit containing at least a magnetic gap, a frame connected to the magnetic circuit, and an integral unit consisting of a ring shaped voice coil bobbin unit which is wound around with coil to be coupled in the magnetic gap, and a diaphragm unit formed in the shape of an inverse letter “U” disposed on an upper edge of the voice coil bobbin unit. This speaker provides enhanced rigidity, a reduction in production/assembly cost, and an improved sound pressure level.

Abstract: A loudspeaker comprising a frame, a motor structure, an upper suspension, a lower suspension, a diaphragm, and, a voice coil carrying a wire winding and being formed with a number of circumferentially spaced vent bores spaced from the winding. An adaptor is provided having a wall with a first end mounted to the former of the voice coil, a second end, and an intermediate portion extending between the first and second ends which overlies the vent bores of the former and is radially offset thus forming a passage between the wall of the adaptor and a portion of the outer surface of the former. A ledge is formed at the second end of the adaptor wall for mounting the free ends of the diaphragm and lower suspension, which, in turn, position the voice coil within the magnetic gap in the motor structure.

Abstract: A speaker apparatus includes a frame having a magnetic circuit, a voice coil bobbin installed in the frame to be magnetically coupled to the magnetic circuit, and a diaphragm movably installed in the frame and fixed to the voice coil bobbin so as to be driven by activating the magnetic circuit. The diaphragm has a positioning portion that had been used for securing the diaphragm relative to the magnetic circuit during an installation of the diaphragm in the frame.

Abstract: A fully integrated, low cost, amplified electro-acoustic loudspeaker is disclosed in which an amplifier circuit (30, 130, 230, 330, 930, 1030), radio-frequency receiver amplifier circuit (430, 530), optical receiver amplifier circuit (630, 730), or network based amplifier circuit (830) is directly mounted on the loudspeaker's magnetic assembly (105, 505, 705, 805), contained within the loudspeaker's moving assembly (20, 29, 629, 42, 45, 50, 65), or a combination thereof. The amplified loudspeaker's magnetic assembly (5, 105, 405, 505, 705, 805, 905, 1005) is utilized as an electro-magnetic interference shield and/or a heat dissipating element for the attached electronic circuitry. In selected embodiments of the amplified loudspeaker system, the former (42) containing voice coil (45) is additionally utilized for convection cooling of the amplifier circuit (30, 230) or receiver/amplifier circuit combination (430, 630).

Abstract: A dome speaker comprises a dome section including a vibrating diaphragm having a dome shape, an annular edge damper section provided surrounding the dome section, an annular coil holder provided between the dome section and the annular edge damper section for holding a voice coil. In particular, the dome section further includes a cap having substantially the same shape as the vibrating diaphragm, said cap being bonded on the said vibrating diaphragm.

Abstract: A voice coil adaptor ring and loudspeaker system of the moving coil type including a cone diaphragm supported by a frame, a voice coil former for supporting a voice coil, and a lower suspension for securing and centering the voice coil former in a magnetic gap while it is displaced by a magnetic circuit. The voice coil adaptor ring is mounted over the voice coil former and comprises a substantially cylindrical sleeve having at least one ledge extending outward from said sleeve for supporting the cone and lower suspension and a plurality of venting passages in fluid communication with a cone volume defined by the cone for venting hot air from the cone volume.

Abstract: A broad band loudspeaker (101) includes a diaphragm (103) driven by coil assembly (125) centered on a pole (131) of a magnet assembly (133) by a low-friction guide (127) depending from a lower end the coil assembly, and a low-friction guide mounted on an upper end of the pole (131). A suspension (107) for the diaphragm (103) includes two or more parallel, resilient suspension members (115a, 115b), extending between the diaphragm (103) and frame (105) and mounted through a pair of resilient mounting pads (119a, 119b, 125a, 125b). The lower guide (127) includes a flexible portion (151a) which acts like a flapper valve of a pump to create a current of cooling air past down the inside of the coil assembly (125), up the outside of the coil assembly and then out of flux gap (130).

Abstract: A horn speaker system includes a dome-shaped diaphragm, a coil bobbin, a phase equalizer, and a magnetic circuit. The coil bobbin is integral with the dome-shaped diaphragm, and a voice coil is wound on the coil bobbin near a free end thereof. The magnetic circuit coacts with the voice coil for producing forces to actuate the dome-shaped diaphragm. The magnetic circuit includes a cylindrical magnet, a first annular yoke attracted to one end of the cylindrical magnet and having a central opening, a plate cooperating with the first yoke in defining a gap in which the coil bobbin is inserted, and a second yoke attracted to an opposite end of the magnet. The magnet, the first yoke, the first plate, and the second yoke jointly make up a closed magnetic circuit. The phase equalizer serves to keep sounds outputted from the dome-shaped diaphragm in phase. The phase equalizer is mounted on the first yoke and has a plurality of slits defined therein.

Abstract: A light and cost effective speaker is provided which is suitable for a vehicle mount speaker, thin, and has a broad reproduction frequency band. Like a cone diaphragm and a center cap or the like, the cone diaphragm having a valley at the junction point with the center cap is integrally mounted with the center cap, and a plurality of voice coils, preferably three or more voice coils, are radially disposed along the valley or at the area near the valley to drive the diaphragm.