US 3649776 A
An omnidirectional loudspeaker is disclosed herein having a pressure wave radiator comprising a pair of circular, vibrating pistons incorporating opposing spaced-apart shaped surfaces wherein each piston carries a cylindrical extension disposed at its center with a voice coil movable in the magnetic gap of a magnetic structure. An outer portion of the shaped surfaces of the vibrating pistons forms an omnidirectional exponential horn for propagating sound in all directions outwardly as the pressure waves are generated by the piston movement, via energization of the respective coaxial voice coils. The voice coils are electrically connected out of phase so as to differentially move the pistons in opposite directions to increase or decrease the pressure components between the opposing piston-shaped surfaces. The pistons are maintained in coaxial relationship by a pair of spider members mounting the extensions of the pistons respectively to rigid supporting structure.
Claims available in
Description (OCR text may contain errors)
United States Patent [151 3,649,776
Burton 5] Mar. 14, 1972  OMNIDIRECTIONAL HORN LOUDSPEAKER  inventor: William D. Burton, 2946 Getrude Avenue,
Los Angeles, Calif. 91214  Filed: July 22, 1969  Appl. No.: 343,346
 US. Cl. ..179/115.5 H, 179/115.5 VC  Int. Cl ..11041' 9/02  Field oiSearch................179/l15.5, 115.5 PS, 115.5 11,
 References Cited UNITED STATES PATENTS 2,956,636 10/1960 Boersma ..181/31 Primary Examiner-Kathleen H. Claffy Assistant Examiner-Thomas L. Kundert Attorney-Roger A. Marrs  ABSTRACT An omnidirectional loudspeaker is disclosed herein having a pressure wave radiator comprising a pair of circular, vibrating pistons incorporating opposing spaced-apart shaped surfaces wherein each piston carries a cylindrical extension disposed at its center with a voice coil movable in the magnetic gap of a magnetic structure. An outer portion of the shaped surfaces of the vibrating pistons forms an omnidirectional exponential horn for propagating sound in all directions outwardly as the pressure waves are generated by the piston movement, via energization of the respective coaxial voice coils. The voice coils are electrically connected out of phase so as to differentially move the pistons in opposite directions to increase or decrease the pressure components between the opposing 3,350,514 10/1967 Cooke ..179/1 15.5 pistomshaped Surfaces. The pistons are maintained in coaxial FOREIGN PATENTS OR APPLICATIONS relationship by a pair of spider members mounting the extensions of the pistons respectively to rigid supporting structure. 272,263 6/1927 Great Britain 179/1 16 11 Claims, 8 Drawing Figures 59 5' 7 41 m m: !I\ 1 m in m '1 i l 1 1 i F I I l 1, l 1 l i 1 52, I Z5 Z6 52. i g, l 1] 1 1 40 i1 18 25 25 T M H! 56 -J 1 I 1 5 20 1 r 55 4 4 I 5 1 1 l r 1 1 I l l 1 [7 S 1 1 S L 1 l Q m 16 n\ g 19 51 4 e a PATENTEDMAR 14 I972 SHEET 2 0F 2 l V/LL/AM 0. BURTON IN v/ mu (m Q /QM OMNIDIRECTIONAL HORN LOUDSPEAKER BACKGROUND OF THE INVENTION 1. Field ofthe Invention This invention relates to the field of electroacoustic transducers or acoustic reproducers and, more particularly, to a novel loudspeaker apparatus providing acoustic energy generation in a toroidal propagation pattern by employing differentially moving pistons having opposing shaped surfaces functioning as a pressure wave generator and an exponential horn.
2. Brief Description of the Prior Art In general, conventional loudspeaker construction employs a single vibrating cone as piston to reproduce sound by mechanical motion of the relatively loosely suspended cone. The cone piston is generally made of paper or prepared cellulose, folded or formed to cone shape, so that an adequate degree of rigidity may be obtained without a significant increase in mass. The degree to which a rigid piston of this type produces sound is determined by its size, how it is baffled and the magnitude of the electromotive driving force. Baffling, in general, is a means of preventing the rear wave of sound from interfering or cancelling the front wave. Baffling may take the form of absorbing the rear wave, shielding the rear wave from the front, or processing this wave in such a manner so that it becomes in-phase with the front wave.
Since the sound output of a vibrating piston is governed by the piston size and excursion, increasing the piston diameter increases the acoustic radiation. Under these conditions, the acoustic power output for a given frequency and excursion will vary directly with the radius of the piston. Theoretically, it is possible to increase the radiation for a given frequency at will by utilizing larger and larger diaphragms or cones with increasingly improved reproduction at low frequencies. Practically, however, there are physical limitations imposed on making conventional cones too large. Molded paper cones become physically unstable and depart from true pistons when they become too large, since they begin to flex within themselves. The larger the cone, the deeper they must be made to maintain an acceptable measure of mechanical stability. In order to improve on the mechanical stability, it is necessary to utilize reinforced cones, and this procedure increases the mass and decreases the output. With its accompanying heavy magnet structure, the large-size and cone-type speaker becomes excessively bulky, deep and heavy. The resulting structure, even if successful, is both difficult and expensive to manufacture.
Conventional cone loudspeakers employ a magnetic structure which produces a radial magnetic flux field within a closely spaced gap. A voice coil, carried on the single cone, is im mersed in the gap and electrical signals applied to the coil produce motor action in cooperation with the magnetic field with resulting acoustical output as the cone reciprocally moves accordingly. Since the maintenance of the voice coil in the magnetic gap is critical, conventional spiders" or supporting members are required to mount and center the voice coil within the magnetic gap. Since the voice coil is carried on the vibrating cone, any motion of the cone tends to move the voice coil out of the magnetic gap which results in inefficient system operation.
Attempts have been made in the past to provide cone movement and to maintain the voice coil in the magnetic gap by employing a long voice coil of many wire turns which insures that at least a percentage of the coil will be in the gap at all times. However, this practice has been found to be inefiicient since only a part of the coil is actually used. Another attempt to maintain the complete coil in the magnetic gap has been to employ a long magnetic gap with a relatively short coil so that the coil can move up and down in the gap. This latter practice has been found unsuitable since a relatively heavy magnet structure is required in order to properly saturate the enlarged gap with a magnetic force field.
Another problem encountered with conventional electroacoustic reproducing systems involves acoustical radiation propagation so that the pressure wave variations generated by the vibrating cone are propagated in a desired directional pattern. Normally, pressure waves generated by the vibrating cone as a radiator travel in the direction of cone movement. To this end, it is a customary practice to employ an exponential horn which includes a rigid continuous sidewall outwardly flared or curved from the peripheral edge of the vibrating cone so that the center of the cone is coaxial with the structure of the exponential horn as an acoustic coupling device. Such a horn is highly advantageous but presents additional structure to that of the loudspeaker and is generally considered an additive structure to the loudspeaker rather than an integral structure therewith.
Therefore, it can be seen that a longstanding need is present for providing an acoustical energy system which vastly improves efficiency of the system by maintaining the voice coil more nearly within the magnetic gap at all times, by reducing the mass of the cone to be driven and by improving the loudspeaker design to include directional energy wave propagation means such as an integrally formed exponential horn.
SUMMARY OF THE INVENTION Accordingly, the problems and difficulties encountered with conventional loudspeaker system both in physical construction and in energy radiation are obviated by the present invention which provides a novel omnidirectional exponential horn loudspeaker for generating pressure wave variations and for dispersing sound or acoustical energy radiation in response to the variations in a generally circular or omnidirectional propagation pattern outwardly from the center of the loudspeaker radiator. In one form of the invention, the loudspeaker comprises a pressure wave radiator having a pair of cooperating movable, circular pistons wherein shaped surfaces of the pistons are arranged in opposing spaced-apart relationship so as to produce pressure wave variations therebetween when the pistons are differentially moved with respect to each other. The configuration of an outer portion of the piston-shaped surfaces, in cross section, further provides an exponential horn so that the pressure waves developed by the relative movement of an inner portion of the pistons are translated into transverse acoustical energy wave propagation substantially normal to piston movement. The center of each of the shaped pistons includes an elongated cylindrical extension arranged in telescoping relationship so that the pistons are coaxially disposed with respect to each other and spider members are connected between the respective extensions and supporting structure to physically mount the pistons on the supporting structure. A voice coil is carried on each of the extensions so as to reside within a circular magnetic gap defined by magnetic structure carried on the supporting structure. The voice coils are electrically connected out of phase so that the differential movement of the coils when energized is translated into reciprocating differential movement of the pistons via the telescoping extensions.
Therefore, it is among the primary objects of the present invention to provide a novel electroacoustic reproducer having a pressure wave radiator comprising a pair of differentially moving pistons coaxially disposed with respect to each other adapted to produce acoustic energy perpendicular to the movement of the pistons.
Another object of the present invention is to provide a novel electroacoustic reproducer incorporating differentially movable pistons incorporating a pair of coaxial voice coils electrically connected out of phase which are disposed within the magnetic gap of a magnetic structure.
Still another object of the present invention is to provide a novel loudspeaker having differentially movable pistons disposed in opposing relationship so as to define an annular space therebetween for generating acoustical pressure waves and for propagating such waves outwardly in a direction normal to the pressure waves produced by differential displacement of the pistons.
Yet another object of the present invention is to provide a novel toroidal loudspeaker having an integrally formed pressure wave radiator portion and exponential horn portion for dispersing acoustical energy generated by the radiator portion.
A further object of the present invention is to provide a novel omnidirectional exponential horn loudspeaker for radiating sound or acoustical vibrations in a generally circular or omnidirectional propagation pattern outwardly from the center of the loudspeaker radiator.
BRIEF DESCRIPTION OF THE DRAWINGS The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The present invention, both as to its organization and manner of operation, together with further objects and ad vantages thereof, may best be understood by reference to the following description, taken in connection with the accompanying drawings, in which:
FIG. I is a transverse cross-sectional view of the novel omnidirectional exponential horn loudspeaker of the present in vention;
FIG. 2 is a plan view, partially broken away, taken in the direction of arrows 22 of FIG. 1 showing details in elevation of one loudspeaker piston and a cutaway portion of the supporting structure therefor;
FIG. 3 is an elevational view partially in cross section taken in the direction of arrows 33 of FIG. 1 showing details of a portion of the other loudspeaker piston, a spider member for supporting the piston, and a portion of the magnetic structure;
FIG. 4 is an elevational view partially in cross section taken along plane 4-@ of FIG. 1 showing the coaxial arrangement of the voice coils within the circular gap of the magnetic structure;
FIG. 5 is a cross-sectional view partially in elevation taken along line 55 of FIG. 1 showing further details of the magnetic structure;
FIG. 6 is a transverse cross-sectional view of a portion of another exemplary embodiment of the omnidirectional exponential horn loudspeaker with compliant means formed in the loudspeaker pistons between the inner and outer peripheries thereof;
FIG. 7 is a schematic representation of the two cylindrical extensions carried on the loudspeaker pistons respectively as used in both exemplary embodiments of the loudspeaker construction showing the manner in which the voice coils may be wound on these extensions and the manner of interconnecting the voice coils so as to attain telescopic movement of the cylindrical extensions in opposite directions to each other; and
FIG. 8 is an alternate schematic representation of the two cylindrical extensions of the loudspeaker pistons as used in both exemplary embodiments of the loudspeaker construction showing an alternate manner in which the voice coils may be wound on these extensions and interconnected so as to obtain movement of the cylindrical extension in opposite directions to each other.
DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 15 inclusive, an exemplary embodiment of an omnidirectional exponential horn loudspeaker in accordance with the present invention is illustrated having a magnetic structure and pressure wave generating pistons for transducing electrical signals supplied from a suitable amplifier into acoustical vibrations.
In F IG. 1, a suitable magnetic structure is indicated in the general direction of arrow 10 which is preferably a permanent magnet. However, it is to be understood that an electromagnet may be used, if desired. The permanent magnetic structure includes a cup-shaped member 12 having an internal cavity wherein an annular lip 13 defines the entrance thereto. The lip 13 serves as the south magnetic pole of the magnetic structure and is indicated by the letter character S. Generally, a cylindrical portion 14 occupies part of the cavity and is integrally formed with the magnetic structure so as to be centered within the cavity of the cup-shaped member. The lower end of the cylindrical portion 14 may be attached to the inner concave surface of the cup-shaped member by welding, or the entire magnetic structure may be cast, molded or machined to include cylindrical member 14. Cylindrical member 14 is formed with a reduced diameter portion 15 wherein the free end thereof constitutes the north magnetic pole of the magnetic structure as indicated by letter character N. Portion 15 projects between the opposing surface of annular lip 13 in spaced-apart relationship therewith to define a circular gap 16 and in such a manner that the magnetic pole portion I5 and the south magnetic pole portion represented by annular lip 13 are coaxial.
Disposed on top of annular lip 13 is a mounting ring 17 having a central opening aligned with the gap 16. Mounting ring 17 is employed for supporting a first piston 18 via a cylindrical extension 20 and a spider member 21 having its opposite ends attached to the ring 17 and extension 20, respectively. The spider member 21 is made of resilient material and has compliant means 22 formed therein for limiting displacement of the cylindrical extension 20 and loudspeaker piston 18 to which it is attached.
A post 23 is attached at one end to magnetic structure portion 15 and extends upwardly through the gap and the mounting ring opening to terminate in a fastener arrangement 24 for securement with a spider member 25 adapted to movably support one end of a second loudspeaker piston 26. The spider member 25 includes a compliant means 27 and the piston 26 further includes an elongated cylindrical extension 28 adapted to axially move within the central bore of extension 20 in reciprocal telescopic relationship therewith. It is to be particularly noted that the terminating free ends of both cylindrical extensions 20 and 28 reside within the circular gap 16 in coaxial relationship with respect to each other and with respect to the gap and magnetic structure portion 15. The ends of each of the cylindrical extensions 20 and 28 residing within the gap 16 serve to mount a pair of voice coils 30 and 31 respectively. The cylindrical extensions are moved axially through the magnetic gap 16 in response to the motor action created by the magnetic field within the gap and in response to electrical signals imposed across the coils. The coils are wound about the external surface of the lower portion of each cylindrical extension and are, preferably, entirely within the magnetic field created by the north and south poles of the magnetic structure when the cylindrical extensions are at rest. When the coils are energized by suitable electrical signals, the extensions will move in a differential manner upwardly and downwardly with respect to the cylindrically shaped north pole portion 15 carrying the central or inner central portions of the pistons therewith. As will be described later, the coils are electrically connected out of phase so that the differential movement between the pair of cylindrical extensions move in opposite directions in a telescoping action or relationship. However, at no time will either of the coils be entirely out of magnetic gap.
Inasmuch'as the central inner portions of the loudspeaker pistons 18 and 26 are carried by the respective extensions 20 and 28, the application of electrical signals to the coils will cause axial motion of the extensions which, in turn, will move the pistons together and away from each other, thereby transducing electrical signals to acoustic vibrations or sound.
The loudspeaker pistons 18 and 26 are substantially dish shaped in cross section and include circular compliant means 32 and 33 formed along the edge marginal region of their circular peripheries. The circular peripheries of the pistons are secured to supporting structure taking the form of a plurality of upright posts, such as post 36 which are arranged in fixed spaced-apart relationship about the circumference of the loudspeaker and by means of an upper support plate 37 and a lower support plate 38. Fasteners, such as fastener 39, secure the extreme peripheral edge marginal region of each of the pistons to the posts 36 so that the edge is disposed between a surface of a respective plate and a sleeve 40 carried about the post 39. Therefore, by means of the peripheral edge marginal regions of each of the pistons being secured to the supporting structure via fasteners 39 and posts 36 and by means of the central portion of each of the pistons being mounted on the magnet structure via spider members 21 and 25, it can be seen that the pistons are mounted so that their center sections or inner portions are adapted to vibrate differentially in response to the motor action of the voice coils 30 and 31 reacting in the magnetic field of the magnetic gap 16. It is also to be understood that the support plates 37 and 38 may take the form of a simple ring which interconnects the plurality of post 36 or, as illustrated, each plate may be provided with a plurality oflightening holes 41.
A feature of the present invention resides in the fact that not only are pressure waves generated between the opposing shaped surfaces of the pistons 18 and 26 but pressure waves are generated on the opposite sides of the pistons so that such acoustic energy radiates through or past the top and bottom plates 37 and 38. Therefore, it is apparent that the novel loudspeaker of the present invention has a unique facility of being operated unbaffled to provide an omnidirectional radiating characteristic. In other words, advantage is taken of both the front and rear pressure waves when the pistons are vibrated and no means are required to dampen, absorb or otherwise cancel the rear pressure wave as is the customary case in connection with conventional cone loudspeakers.
However, the primary development of acoustical pressure waves resides in a throat area T defined between the opposing surfaces ofthe central inner portions of the pistons 18 and 26. As the pistons are moved together, air occupying a throat area T is compressed and as the opposing surfaces move apart, the air within the throat area is released or permitted to expand. In other words, opposing surface areas of the pistons extending from the respective extensions outwardly for approximately one-third of their respective diameters, constitute a pressure wave generator or radiator. From the end of the throat area T, the remaining two-thirds of the outer surface area to the peripheral edge of the pistons defines an exponential horn between the opposing surfaces. These latter surfaces are shaped to include outwardly extending opposite flared portions defining a circular mouth area indicated by the letter M. It is to be understood that both the throat area T and the mouth area M are coextensive and that the combined areas are substantially annular about the coaxial extensions and 28.
The differential action of the central inner portions of the pistons defining area T results in a doubling of the physical travel which results in doubling the pressure developed in the throat area as compared to the development of pressure by either piston portion alone. This results in an acoustical output which is proportional to the square of the pressure wave variations and such a result is effective without employing an elongated magnetic gap or an increase in coil length or increase in the weight of the magnetic structure. In other words, a substantially smaller amount of physical motion is required in the magnetic gap as compared to conventional voice coil move ment in conventional gaps to produce the required effective travel between the opposing wall portions of the pistons.
The two opposing outer wall portions of the pistons form therebetween an exponential horn with the result that the pressure wave variations induced when these pistons move either together or apart, produce alternate highand low-pressure conditions. Pressure waves that are generated in the throat area are propagated outwardly through the horn or mouth area M and radiate from the horn as acoustical energy. The acoustical energy waves propagated by the exponential horn portion are actually at right angles to the pressure wave variations produced in the throat area T. The pressure waves generated by the pistons 18 and 26 are generated in a vertical direction whereas the sound generated by the pressure wave propagation from the area M is horizontally directed outwardly and irregularly. This situation assists in the elimination of some of the conventional wave-cancellation problems that normally would be encountered in conventional loudspeaker systems where the two pressure wave propagations are in the same plane. Since the rear side of each of the pistons is open to atmosphere, back pressure waves are propagated in the form of acoustical energy and such back wave energy is not a detriment and does not require absorption, cancellation, or other means of baffling, since it is propagated at right angles to the main wave propagation.
Referring now to FIG. 6, an alternate exemplary embodiment is provided of the present invention which differs from the embodiment illustrated in FIGS. 15 in that instead of the loudspeaker pistons having compliant means at their outer peripheries, compliant means 45 and 46 are provided in each of the respective pistons 26 and 18 which are formed substantially midway between the center and peripheral edge of each of the respective pistons. By providing the circular compliant means 45 and 46, each of the pistons is reduced in its pressure wave generating portion so that only the portion of each piston residing between the respective extensions 20 and 28 and the respective compliant means 45 and 46 will vibrate or displace. Therefore, the energy required to displace the reduced mass of the pistons is reduced and at the same time, loudspeaker efficiency is increased and the high-frequency response thereof is greatly improved. Pressure waves are generated only within the throat area T in response to displacement of the inner piston portions while the outer piston portions defining mouth area M remain substantially stationary and serve as an exponential horn for propagating acoustical energy developed by pressure wave variations in the throat area.
Referring to FIGS. 7 and 8, the loudspeaker cylindrical extensions with the voice coils thereon are illustrated schematically showing different ways of winding the voice coils and interconnection thereof to each other so as to provide for loudspeaker cone motion in opposite directions as required by this invention. Hence, in both exemplary embodiments, cylindrical extension 20 has wound thereon in one direction voice coil 30, the free end of extension 20 being shown at 47. Cylindrical extension 28 has voice coil 31 wound thereon in the same direction as voice coil 30. The free end of extension 28 is shown at 48. The voice coils are shown series interconnected so as to provide leads 50 and 51 which conventionally attach to either a transformer or an amplifier. Although the voice coils are shown series connected in such a way as to provide current flow in each voice coil in directions opposite to each other for achieving cylindrical extension and consequently piston movement in opposite directions to each other, the voice coils could be parallel connected or individually connected to a transformer or an amplifier to achieve the same result providing the left-hand rule of orthogonal relationships between magnetic flux, direction of current flow in the voice coils, and direction of motion of the voice coils are maintained.
In FIG. 8, voice coil 30 is wound in the same direction as in FIG. 7, but voice coil 31 is wound in opposite direction to the direction of voice coil 30. Hence, the two voice coils are series connected in another way so as to provide leads 52 and 53 which connect in the same manner as leads 50 and 51. This arrangement provides an alternate way of winding and interconnecting the voice coils to provide the same effect of cylindrical extension and consequently cone motion in opposite directions to each other as required by the invention. Considerations for making parallel connections of the voice coils and for independently connecting the voice coils to external means are the same as those mentioned hereinabove with respect to abiding by the left-hand rule.
Preferably, the voice coils 30 and 31 are not physically coupled together but represent separate coils which are independently connected to their own output transformers. The separate coils are shown in FIGS. 1 and 6; however, it is understood that the separate coils are out of phase with each other so that differential movement of the central portions of the pistons is experienced via the movement of the respective extensions.
In view of the foregoing, it can be seen that the present invention provides a novel loudspeaker having a pressure generator or wave radiator defined between differentially moving pistons and which further provides an exponential horn defined by outer portions of the pistons. When the pistons are at rest, the free ends of the extensions 20 and 28 carrying voice coils 3t] and 31 generally reside within the confines of the magnetic poles within the magnetic gap 16 surrounded by the magnetic field created by the magnetic structure 10. When electrical signals are applied to the coils, axial motion of the extensions occurs, thereby moving the opposing walls of the pistons defining throat area T upwardly and downwardly depending upon the direction of current flow of the electrical signal. Spider members 21 and 25 centrally support the extensions and hence the central portion of the pistons and are employed to keep the voice coils centered laterally within the magnetic gap as well as providing structural support for the pistons. The convex opposing surfaces of the pistons form a 360 or an omnidirectional exponential horn. The voice coils are responsive to electrical signals and are electrically connected to each other in a manner so as to provide motion of the cylindrical extensions along their longitudinal axes within the magnetic structure Motion of the extensions is imparted to the pistons in opposite directions to each other for converting the electrical signals to acoustic pressure waves and for providing an acoustic power output from the exponential horn in an omnidirectional beam pattern. The acoustic power output is proportional to the square of the effective displacement distance between the pistons.
While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.
What is claimed is:
1. An omnidirectional exponential horn loudspeaker construction comprising:
a magnetic structure;
a pair of circular loudspeaker pistons having opposing convex surfaces which form said omnidirectional exponential horn;
each of said loudspeaker pistons having a cylindrical extension carried at its center with a voice coil wound on the free end of each of said extensions;
said extensions being coaxial with each other and at least portions of said voice coils extending within said magnetic structure for subjecting said voice coils to the magnetic field thereof; and
said voice coils being responsive to electrical signals and being so connected so as to impart motion to said loud speaker pistons in opposite directions to each other for summing generated pressure developed by said pistons when approaching each other to provide an omnidirectional beam of acoustical power outward from the loudspeaker construction which is proportional to the square of the resultant displacement of said loudspeaker pistons.
2. The loudspeaker construction as defined in claim 1 wherein.
one portion of said magnetic structure is coaxial with said cylindrical extensions and another portion of said magnetic structure is circumjacent at least a portion of said cylindrical extensions.
3. The loudspeaker construction as defined in claim 2, in-
a spider member carried on said magnetic structure and connected to said extensions for limiting motion of each of said loudspeaker pistons for restoring said loudspeaker pistons to their initial positions and for providing structuralsupport therefor. 4. The invention as defined in claim 1 wherein a central inner portion of said opposing surfaces defines a throat area therebetween adapted to generate pressure wave variations; and wherein an outer portion of said opposing surfaces define a mouth area therebetween adapted to propagate acoustic energy in a plane normal to the pressure waves in response to said pressure wave variation.
5. The loudspeaker construction as stated in claim 4,
a pair of spaced-apart support members, each being formed with a plurality of passages therethrough;
said magnetic structure is attached to one of said support members.
6. The invention as defined in claim 5 wherein the center portion of said pistons are movably carried on said magnetic structure and the peripheral edge marginal region of said pistons are fixed to supporting structure.
7. In an electroacoustic reproducer, the combination comprising:
a pair of circular, coaxial pistons having opposing wall sur faces arranged in spaced-apart relationship;
means movably supporting the central portion of said pistons so as to permit differential movement therebetween; and
means mounting said supporting means and cooperating therewith for producing a motor action to move said pistons in response to applied electrical signals;
said supporting means includes a pair of elongated cylindrical extensions coaxially arranged in telescoping relationship, each extension of said pair being carried by a selected end fixed to a respective piston substantially at its central portion;
said mounting means includes a magnetic structure defining a circular magnetic gap occupied by the terminating free ends of said extensions;
spider members connected between said extensions and said magnetic structure for movably mounting said extensions thereon; and
voice coils carried on the free ends of said extensions within said magnetic gap.
8. The invention as defined in claim 7 wherein said voice coils are electrically connected out of phase.
9. The invention as defined in claim 8 wherein said pistons define a pressure wave generator between opposing piston central portions and further define an exponential horn from said central portions to the peripheries of said pistons.
10 The invention as defined in claim 9 including means secured to and between the peripheries of said pistons in fixed spaced parallel relationship so as to support said pistons and to maintain the peripheries of said pistons in fixed spaced-apart relationship.
11. The invention as defined in claim 10 including compliant means formed in each of said pistons midway between their respective centers and the periphery of each of said pistons.