WO2010076656A2

WO2010076656A2 - Improved inertial type acoustic transducer

Info

Publication number: WO2010076656A2
Application number: PCT/IB2009/007985
Authority: WO
Inventors: Robert Katz; Stephen Saint-Vincent
Original assignee: Robert Katz
Priority date: 2008-12-31
Filing date: 2009-12-30
Publication date: 2010-07-08
Also published as: WO2010076656A3

Abstract

The improved suspension system includes a sprung suspension disc associated with a cup partially surrounding a magnitc circuit which allows axial movement of the circuit but retains its rotational status and prevents cocking. Further, the invention provides a structure that reduces the height and/or size of a transducer and includes a mounting disc and receiving apparatus which provide advantages for manufacturing and installation. Apertures int he housing are artfully provided to conduct convective currents for cooling. Finally, the invention comprises a reduction in the number of parts by disclosing the creation of a unitary part in place of several components.

Description

TITLE OF THE INVENTION

Improved Suspens ion System for Inertia! Type Acousti c Transducer FIELD OF THE INVENTION

The present invention relates generally to electrodynamic, ineitial type actuators used to produce sound. Specifically, the actuators are capable of converting energy between electrical and mechanical form utilizing any of a variety of magnetic circuits or magnetic motor structures and a multi-component suspension system. BACKGROUND OF THE INVENTION

Loudspeakers and momentum type transducers historically have utilized two basic electrodynamic structures based upon a magnetic circuit described in US Patent 2,698,917 (A.T. Van Urk, et al) ihat describes the use of a ferromagnet having a substantially flat, thin permanent magnet, where the smallest dimension of the magnet is parallel with the direction of magnetization. Of the two most basic descriptions of the substantially flat magnet, the most common is the use of an annular magnet adjacent to a bottom plate with a center post to form one magnetic pole and a top plate with a central hole, creating an annular air gap with the center post to form the second magnetic pole. The second basic description is a disk shaped magnet without a central aperture that has a first pole defined as a top plate having the same as or larger diameter than the magnet, and a second pole formed by a pot type structure where the magnet is centrally aligned with the pot and an annular airgap is formed between the upper edge of the pot and the magnetic top plate.

The annular magnet type electro-dynamic motor structure has found a very wide use because the magnet material is inexpensive, and because of the fact that assembly and magnetization are simple to accomplish. However, this design has significant drawbacks. The magnetic leakage flux at the outer edge of the magnetic assembly is strong. When this structure is placed near a CRT or Plasma type video display, the display equipment is degraded. Further, the low magnetic flux output of the ferromagnetic material requires substantial cross-sectional area of the magnet sysrem (transversely to the axis of symmetry). The resulting requisite large physical dimensions are problematic for many new product design considerations.

The poL type magnetic structure re-gained significant commercial viability with the introduction of rare earth magnets, primarily those containing Neodymium, Iron and Boron. US Patent 5,390,257 (Oslac, et al) describes a system that is based on an axially magnetized, coin or disk-shaped magnet, usually of NdFeB material. The high flux capacity of the NdFeB magnet enables reasonable efficiency with the magnet contained within the voice coil dimension. However, since the area of the magnet is limited by the coil diameter, the level of magnetic flux is also limited. It is common to add an axial hole centrally through the assembly to obtain ventilation but this addition will reduce the magnetic flux, overall efficiency, and bandwidth. On the positive side, the system has a moderate depth and cross- sectional area in relation to the coil diameter, something which is very advantageous in some applications.

As is well known in the art, the force generated by an electrodynamic transducer is a product of the current, I, length of coil wire, L and flux density, B so that F=iL®B. The length of the coil wire that is within the annular magnetic gap is defined as the length, L. This force is what creates the movement of the coil and subsequently generates sound. Building on this concept, inertial voice coil actuators have been used to acoustically stimulate semirigid structures to radiate sound. In this application, voice coil actuators have been attached to structures that are relatively large to act as a soundboard e.g. a wall in a room. The wall of the room, when acoustically driven, radiates sound. As is well known in the art, the force generated by an electrodynamic transducer is a product of the current, I, length of coil wire, L and flux density, B so that F=iL®B. The length of the coil wire that is within the annular magnetic gap is defined as the length, L. This force is what creates the movement of the coil and subsequently generates sound. Any magnetic circuit (as used in this context, magnetic circuit is meant to include magnetic motors) which operates on this theory of producing movement against a soundboard in order to create sound can be employed with the suspension system of the present invention although some may be used with more success than others.

A number of inventions for voice coil actuators have been patented among them U.S. Patent No. 2,341,275 to Holland for Sound Reproducing Instrument; 3,609,253 for Loudspeaker with Improved Voice Coil Suspension; 3,728,497 to Komatsu for Dynamic Loudspeaker Using Wall as Diaphragm; 4,297,537 to Babb for Dynamic Loudspeaker; 4,951,270 for Audio Transducer Apparatus; 5,335,284 to Lemons for Coneless, No-Moving- Parts Speaker; and 5,473,700 Fenner, Jr. for High Gain Transducer and U.S. 3,524,027 to Thurston, et al.

US Patent 5,51 1 1,131, Kohara et al., describes a magnetic structure that utilizes two opposing polarity magnets for generating a repulsion magnetic field at the voice coil. This particular patent does not have a magnetic return path, thus making it unsuitable for applications where stray magnetic fields need to be minimized. US Patent 5,434,549 Hirabayashi et al., describes a moving magnetic type actuator that utilizes a plurality of opposing magnets disposed on a common armature that is free to move on a longitudinal axis. The magnets are surrounded by a plurality of coils plus one which are connected so current flows in a direction in accordance with magnetic flux of the permanent magnets as the boundary. The mass of the moving magnets makes it unsuitable for broadband frequency response as an inertial type transducer.

US Patent 7,039,213 B2 Hyre et al., describes a magnetic circuit in which the top plate of a loudspeaker magnetic circuit contains a rabbet around the perimeter of the top plate, forming a variation in the intensity of the magnetic flux along the height of the top plate. This circuit produces the magnetic flux variation along the top plate height from a single biasing magnet.

Although these voice coil actuators have certain contextual drawbacks, each may employ the suspension system of the present invention with varying degrees of success.

It is known to employ a compliant suspension structure formed in the base wall of a momentum type transducer that is in closest proximity to the soundboard. At the centerline of the base wall there usually is either a threaded insert or protruding threaded bolt. The momentum transducer is cantilevered off a threaded rod, which is mechanically attached to the soundboard. Two problems arise with this design; it significantly increases the transducer's standoff height and profile and, further, forces acting normal to the protruding threaded element are amplified such that they may cause structural failure in the mechanical attachment.

In practice, the annular magnet, magnetizable plates, external housing and structural attachment point as presently known in the art, comprise a system that is large and heavy relative to the total dynamic force the actuator is capable of generating. If the external housing is mounted on a vertical facing surface such as a wall, large bending moments will be placed on the structural attachment point which may be translated to the coil. In sum, the present state of the art provides electrodynamic transducers that are plagued with well known problems of low power handling, limited frequency response, high levels of sound distortion, substantial size and mass, mechanical complexity and high production costs.

Recent innovations include magnetic materials that have produced magnets with substantially greater magnetic energy than ceramic magnets. These magnets have necessitated the redesign of the magnetic circuit to take advantage of the higher magnetizing flux while reducing the volume of the magnet material consumed, thus reducing its size while simultaneously increasing its force density per unit volume. However, these prior art voice coil actuators are not typically designed with suspension systems adequate for actuators driving relatively large structures such as walls. Consequently, their application in those contexts results in some of the same short falls as was previously known, especially relative to sound quality and distortions. SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a unitary or minimum piece outer housing to simplify production and assembly, and to provide a robust assembly.

It is another object of the present invention to provide a novel means to increase the dynamic force output of momentum type acoustic transducers within a small package size.

It is a further object of the present invention to provide a means of improved power handling of the momentum type transducer by way of improved ventilation.

Another objective of the present invention is to provide suspension means for maintaining the radial and axial alignment of the electrically conductive coil or coils within their respective airgaps.

Another objective of the present invention is to accomplish the aforementioned objectives in a way that may be employed with a variety of magnetic circuits and magnetic motors.

It is a final objective of the present invention to provide a convenient and effective mounting and installation means for the transducer to a soundboard.

The present invention comprises a novel suspension system that may be employed with a host of magnetic circuits (as used herein, magnetic circuit encompasses magnetic motor). The suspension system includes ventilation apertures as well as axial displacement advantages. It is preferably equipped with a mounting disk that can be easily coupled or removed from a receiving apparatus associated with a soundboard. The construction of the present invention reduces the heating problems associated with prior art and the distortion that can occur when a transducer is cantilevered from a single point. In a most preferred embodiment, many of the components are of unitary structure accomplished through molding or other suitable processes which significantly reduces costs associated with manufacturing as well as increases the ease of assembly. Further, unitary structure increases uniformity within a unit even further improving the output characteristics. By way of the molding process materials can easily be changed to best match the acoustic properties of the materials to the application.

Other objects, features, and advantages of the present invention will be readily appreciated from the following description. The description makes reference to the accompanying drawings, which are provided for illustration of the preferred embodiment. However, such embodiment does not represent the full scope of the invention. The subject matter which the inventor does regard as his invention is particularly pointed out and distinctly claimed in the claims at the conclusion of this specification.

BRIEF DESCRIPTION OF THE DRAWINGS

In the appended drawings:

Figure 1 is a top perspective view of an inertial acoustic transducer according to a non-restrictive illustrative embodiment of the present invention; '

Figure 2 is a bottom perspective view of an inertial acoustic transducer according to a non-restrictive illustrative embodiment of the present invention;

Figure 3 is a top perspective view of an inertial acoustic transducer and receiver mounting apparatus according to a non-restrictive illustrative embodiment of the present invention;

Figure 4 is a schematic cross-sectional view taken along line A-A of Figure 1 according to a non-restrictive illustrative embodiment of the present invention;

Figure 5 is a schematic cross-sectional view taken along line A-A of Figure 2 according to a non-restrictive illustrative embodiment of the present invention;

Figure 6 is a perspective view of the second sprung suspension means according to a non-restrictive illustrative embodiment of the present invention;

Figure 7 is a perspective view of an electrically conductive voice coils wound on a former according to a non-restrictive illustrative embodiment of the present invention;

Figure 8 is a schematic cross-sectional view taken along line A-A of Figure 2 according to a non-restrictive illustrative embodiment of the present invention;

Figure 9 is a schematic cross-sectional view taken along line A-A of Figure 2 according to a non-restrictive illustrative embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION A top perspective view of the improved suspension system 1 of the present invention is illustrated in Figure 1 and Figure 4 which shows a cross section line AA through the center of the inertial or momentum type acoustic transducer 10. Referring now to Figs. 1, 2 and 4 the suspension system 1 comprises a housing 18 and a sprung suspension disc 12 having an inside edge 13 and an outside edge 15. The discl2 is characterized by at least one and preferably a plurality of perforations, holes 14 or partial perforations. In the preferred embodiment each said perforation 14 is shaped and positioned to be at least partially radial relative to the center and permits axial displacement of at least the inside edge 13. Axially mounted to the sprung suspension disc 12 is a cup element 16 of a magnetic circuit 48 (see Fig. 4) which shall be described further. The cup portion 16 of the magnetic circuit 48 is either mechanically or adhesively mounted to the inside edge 13 of the sprung suspension disc 12 while the outside edge 15 is mounted in a similar fashion to the outer housing 18. The inside edge 13 of the sprung suspension disc 12 affixed to the cup element 16 of the magnetic circuit 48 is able to move axially along the vertical axis (along line 19-19) of the inertial type acoustic transducer 10. Preferably, at least one ventilation opening 20 is seen on a lower portion 21 of the outer housing 18 , as well as at least one ventilation opening 22 at or near an upper edge 23 of the outer housing 18. It is certainly within the scope of the present invention to include a plurality of ventilation openings 20 positioned otherwise on the outer housing 18 either in addition to or instead of those on the upper edge 23 or the lower portion 21.

Figure 2 illustrates a lower perspective view of the inertial acoustic transducer 10. A cross section line BB is taken through the ventilation openings 20. A bottom surface 24 is generally flat and can be adhesively or mechanically mounted to a substrate or soundboard material in order to have the inertial type acoustic transducer 10 operate in the appropriate fashion. Alternatively, the bottom surface 24 may be characterized by a mounting disc 25 of any shape, preferably of generally circular shape. The mounting disc 25 may comprise means to align and affix 26 the transducer 10 to a receiver apparatus 28. Means to align and affix comprise at least one tab or lip, and in the case of the preferred illustrative embodiment, a plurality of helicoidal wedges or tabs 26. (see Fig. 3) Said means to align and affix help with the proper installation of the transducer 10. The plurality of tabs 26 (or helicoidal wedges) are preferably equally spaced.

Figure 3 illustrates the momentum type acoustic transducer 10 and the receiver apparatus 28. The receiver apparatus 28 can be adhesively or mechanically affixed to a substrate that can act as a soundboard. The apparatus 28 permits the easy installation of a mounting disc 25 using for example adhesives, letting the adhesives harden prior to installing the heavier transducer 10. The receiver apparatus 28 is formed of flat surface 30 and a circular receiver portion 32. The receiver portion 32 comprises means for receiving and securing 27 the mounting disc 25. In one preferred embodiment, means for receiving and securing comprises a flexible Hp. In another preferred embodiment, means for receiving and securing 27 comprises an inside surface of the receiver portion 30 and at least one and, preferably, a plurality of receiver openings 34. The openings 34 generally correspond to said tabs 26 and are spaced at intervals equal to the spacing of the tabs 26. When helicoidal wedges are used as tabs 26, then each of said openings comprises at least one mating sloped wedge 36 which match the slopes of the helicoidal wedges 26. In the most preferred embodiment, the helicoidal wedges 26 have a rounded or chamfered front end 38 which facilitate mounting registration of the wedges when the inertial type transducer 10 is twisted into the receiver apparatus 28. The mating sloped wedges 36 are further characterized by a generally vertical abutment wall 44 shaped to receive the front end of the helicoidal wedges 26 and generally formed to front end 38 of the helicoidal wedges 26.

For mounting, the mounting disc 25 of the inertial type transducer 10 is inserted into the receiver apparatus 28 by registering said means to align and affix the transducer 26 with said means for receiving and securing the mounting disc 27. In the preferred embodiment, the tab or plurality of tabs 26 are registered with receiver openings 34. Then the momentum type transducer 10 is rotated, engaging the tabs 26 into the openings 34. When the tabs 26 are helicoidal wedges, each is registered until the bottom surface 24 abuts the flat surface 30. Then the momentum type transducer 10 is rotated engaging the helicoidal wedges 26 into the mating sloped wedges 36. The effect of this compresses the bottom surface 24 of the transducer 10 to the flat surface 30. Said means to align 26 comprises a first overcenter rib 40 and said means to receive comprises a second overcenter rib 42. Preferably, at least one and preferably two over center lock ribs 40 are placed at 180 degree intervals. Figure 2 shows the opposite over center lock ribs 42 which when the inertial type transducer 10 is rotated into place the over center ribs 40 and 42 ride over each other and assist in locking the inertial type transducer 10 into the receiving apparatus 28. Once secured in place with the over center ribs 40 and 42 having being engaged, the mating of the helicoidal wedges 26 in the mating sloped wedges 36 provide compressive force to ensure the bottom surface 24 is firmly and securely in inseparable contact with the flat surface 30. Applying sufficient counter torque to the inertial type transducer 10 will cause the ribs 40 and42 to override each other which then permit easy counter rotation of the inertial type transducer for easy removal. Figure 4 illustrates a cross sectional view of the inertial type acoustic transducer 10 taken at Section AA in Figure 1. The inertial type transducer 10 is characterized by two suspension elements 12 and 46. As previously described, each of the sprung suspension discs 12 and 46 are designed to have its inner diameter at the inside edge 13 move axially when its outer diameter at the outside edge 15 is held fixed.

The suspension disc 12 is affixed to the one end of the internal magnetic structure 48 on its inside diameter 13 as illustrated, while its outside edge 15 is affixed to housing 18. The inside edge 13 of the disc 12 preferably comprises a ring 50 having an inner surface 56 and a flange 52 having an inner surface 58. The cup includes a groove 60. In the preferred embodiment, the inner surfaces 56 and 58 are mechanically and or adhesively affixed to the groove 60 which is shaped to accept these features. Any other locating means known to those skilled in the art can be used to cause concentric alignment of the suspension means 12 and the magnet structure 48. In the preferred embodiment, on the outer edge 15 of the suspension disc 12 a registering ring 54 can be found. It is also preferably mechanically and, or adhesively affixed to the housing 18. A radial groove 62 in the housing 18 further accommodates the fitting of the suspension disc 12.

Now referring to Figure 4 and Figure 6, it should be noted Figure 4 exhibits a cross section view through the inertial type transducer 10 through ventilation holes 20 and 22 on the left side and then through a full section of the housing 18 on the right side and not through the ventilation holes 20 and 22. A second sprung suspension disc 46 holds the internal magnetic structure 48 opposite the end held by the disc 12. The disc 46 is associated with the structure 48 on its inside diameter 13a while a step 64 on the inside surface 49 of the housing 18 forms an abutment for the assembly of the outside edge 15a. For additional positioning, ring 66 on the inside surface 49 of the housing 18 may be provided. Ring 66 further aids with the assembly of the suspension disc 46 into the housing 18, while most preferably another ring 68 assists with the assembly of the inside diameter 13a of the suspension disc 46 to the magnetic structure 48. All interfacing surfaces as described above can be mechanically and, or adhesively affixed one to the other and can be shaped and sized according to the specific needs of the transducer and circuit.

Referring to Figure 5, the magnetic structure 48 illustrated is a magnetic circuit or magnetic motor, designed with the purpose of executing work. The work in this case is to create force actuating a voice coil former 70 to thrust in a reciprocating action at audio frequencies against an inside surface 72 of the bottom surface 24 transmitting these forces in to an adjacent substrate (not shown) which then is able to act as a soundboard. It should be noted that anyone skilled in the art would be able to easily vary the magnetic structure or motor 48 to execute the same work. There are probably dozens of different such structures that may be employed in the present invention provided the selected circuit transmits work to a soundboard in accordance with audio frequencies. In addition to varied magnetic motors using by way of example ceramic or rare earth magnets, magnetorestrictive structures and materials may also be used to achieve the same objectives of creating an inertial type acoustics transducer which would create forces on the inner surface 72 with the goal of creating audio content when in contact with a soundboard. For illustrative purposes but not for limitation, several magnetic structures illustrating a first, second and third preferred embodiment shall be shown.

The magnet structure 48 in Figure 5 is comprised of several components. All are oriented about the center axis of the inertial type acoustic transducer 10. The cup element 16 is generally fabricated out of a ferrous material such as steel. Affixed to an inner surface 74 of the cup 16 is a first permanent magnet 76 with a pole orientation shown in the preferred embodiment of north touching the inner surface 74. Below magnet 76 is a steel disc 78, and below the steel disk 78 is a ceramic disc 80. The ceramic disk 80 is followed by another steel disc 82, then a second permanent magnet 84 with the polar orientation inverse to the first permanent magnet 76. The second permanent magnet 84 then is followed by another steel disc 86.

Between the cup 16 and the permanent magnet 76 a first radial chamber comprising an air space 88 can be found. Surrounding the second permanent magnet 84 another radial chamber 90 is found. The voice coil former 70 extends through radial chambers 88 and 90 and through a first airgap 96 and a second airgap 98. Preferably an annular groove 92 is formed on the inner surface 72 positioned to radially align the voice coil former 70 in the annular groove 94 within the airgaps 96 and 98 of the magnetic structure 48 within the inertial acoustic transducer 10. The voice coil former 70 can be mechanically or adhesively affixed within the groove 94.

The spring suspension discs 12 and 46 suspend and hold the magnetic structure 48 permitting accurate axial reciprocating movement only. The dual suspension discs 12 and 46 therefore impede any cocking of the voice coil former 70 relative to the magnetic structure 48 and more specifically within the airgaps 96 and 98. Therefore the space between the voice coil former 70 and the magnets 76 and 84 within the airgaps 96 and 98 remains constant during reciprocal axial translation of the magnetic structure 48. Referring to Figure 7 and Figure 5, electrically conductive coils 100 and 102 are wound on the coil former 70. The electrically conductive coil windings 100 and 102 are positioned about mid height of the airgaps 96 and 98. Preferably, positioned opposite magnets 76 and 84 across the air gap and centered over the conductive coils 100 and 102 are two steel rings 104 and 106, respectively. The steel rings 104 and 106 are set into a first annular step groove 108 and a second annular step groove 110 and are in contact with the inside wall of the cup 16.

The magnetic structure 48 is comprised of several components preferably cylindrical in shape. All components of the magnetic structure 48 are assembled so as to be in contact with each other and axially aligned. The components include, generally, at least one permanent magnet , at least one steel disc, at least one ceramic disc all appropriately aligned and including polar opposite alignment as necessary. This magnet structure coupled with the cup form a magnetic circuit or magnetic motor. Multiple sequencing of the magnetic circuit components can be repeated as would be obvious to someone skilled in the art so as to increase the force of the magnetic circuit and thus the power of the inertial type acoustic transducer. Additionally, power handling performance of the magnetic circuit can be improved by application of a magnetic fluid 87 within the airgaps 96 and 98, which fluid would be held in place by the resulting magnetic field.

As heat will be generated by the working of the magnetic circuit or motor, the non- restrictive preferred embodiment of the present invention provides for convective cooling of components forming the magnetic circuit and which are sensitive to heat, including but not limited to the permanent magnets. The at least one or the plurality of openings 20 on the bottom portion of housing 18 and the at least one or the plurality of openings 22 on the top portion of housing 18 permits air to enter the housing 18 freely. It is certainly within the scope of the present invention to include a plurality of ventilation openings 20 positioned otherwise on the outer housing 18 either in addition to or instead of those on the upper edge 23 or the lower portion 21.

Referring to Figure 6, a preferred embodiment of the sprung suspension disc 46 is shown. To facilitate the axial movement of an inner diameter 68 of the spring suspension disc 46 relative to its outside diameter a plurality of openings 112 are configured to generally overlap in an inverted "Z" pattern, permitting axial movement of the inner diameter 68 relative to the outer diameter. These openings 1 12 further allow free flow of convective cooling air to flow past the magnetic structure 48. This principal and pattern is preferably repeated in sprung suspension disc 12 and together provide for relatively free movement of air that would either flow into or out of openings 20 and 22, depending on the orientation of the inertial acoustic transducer 10. Other variations of the suspension disc 12 or convective openings 1 12 would be obvious to someone skilled in the art and the above cited illustrative preferred embodiment should not be negatively impacted by way of this.

By way of example, Figure 8 illustrates generally the same inertial type acoustic transducer employing a new magnetic structure 1 14 forms a magnetic circuit characterized by a core 116, a magnet 118, and an electrical current conductive coil 120 wound on a coil former 150. The core 116 is constructed from magnetic flux conductive material and has a first surface 122 and a continuous channel 124 disposed in the first surface 122 which leaves a center column 126 with a bottom surface 128. The channel 124 has a first wall 130, a second opposing wall 132, a top wall 134 and an anti-fringing groove 136.

The magnet 118 is disposed in intimate contact with the second wall 132 so that a magnetic gap 138 is formed between the magnet and the first wall 130. The magnet 118 is cylindrical in shape, is of radial polarization, and comprises a first face 140 of a first magnetic polarity and a second face 142 of a second polarity. The first face 140 is adjacent the second wall 132 and the second face 142 is disposed within the gap 138. The magnet 118 has an upper edge 144 spaced from the wall 134 of the channel 124 forming the anti-fringing groove 136 and a lower edge 146 coextensive with the bottom surface 128 of the center column 126. It should be understood that magnet 118 may be disposed on either first wall 130 or second wall 132. A higher performance design of the present invention will have the magnet 1 18 disposed on the outer first wall 130 of the channel 124. This alternative arrangement creates a stronger magnetic flux across the gap, thus improving its force output for a given current.

The coil 120 is moveably suspended in said gap 138 such that an electrical current in the coil 120 develops a magnetic force on the coil 120 in a direction substantially normal to the radial magnetic flux caused by magnet 128 to displace the coil 120 in response to such magnetic force. Of course, when the coil 120 is coaxially suspended in the gap, the force will be axial and linearly proportional to the current, as is well known.

Preferably, an antifriction bearing 148 is provided for the coil 120 to land upon if a large radial force is imparted to the coil foπner 120 causing large radial displacements. The bearing 148 will prevent the coil former 150 from striking or rubbing the magnet 1 18 or the outer wall 130 of the channel 124.The coil former 150 can be radially suspended by a viscous magnetic fluid 152 if desired. The magnetic fluid 152 is held in suspension by the resulting magnetic flux from the permanent magnet 118. The magnetic fluid will provide a radial restoring force if the coil former 150 is radially displaced in the magnetic gap 138. The bearing 148 of the preferred embodiment is made from a low friction material such as Teflon® by DuPont or similar material.

Various magnetic circuits may be employed in the present invention embodying an inertial voice-coil actuator, and the multi-component suspension system can be formed of generally common components regardless of the circuit arrangement.

Referring to Figure 9 and to emphasize the variability of the magnetic circuit or motor 48 to someone skilled in the art, the magnetic structure 154 may be employed to generate forces on inner wall 72 which permits the inertial type acoustic transducer to transmit acoustics energy into a soundboard in contact with bottom surface 24.

A cross-sectional view of the present invention is illustrated in Figure 9. The illustration presents the present invention of a magnetic circuit or motor 154 as a cross section of a body of revolution. The magnetic circuit consists of a bottom plate 156 with a center post 158 having a first surface 160 forming a proximal wall of an air gap 162, and an anti-fringe groove 164. In the preferred embodiment the groove 164 is characterized by an undercut radius and a taper section 166 between the base of the airgap 162 and the bottom plate 156. An annular permanent magnet 168 has an inner surface 170, a top surface 172, an outer surfacel74, a bottom surface 176 and a beveled surface 178. The bevel surface 178 forms a conical taper which has its central axis coincident with the center line axis of the bottom plate 156. A top plate 180 has an inner surface 182 with a radial dimension 184 that forms the distal wall of the airgap 162, a bottom land 186 that mates with the top surface 176 of the permanent magnet 168, and a beveled interface 188 that is coincident with the bevel 178 of the permanent magnet 168. The inner surface 170 of the permanent magnet 168 comprises a radial dimension 190 larger than the radial dimension 184 of the top plate 180 forming the distal wall of the air gap 162. Those skilled in the art of loudspeaker design will recognize that improvement in the frequency response of the motor can be realized by incorporating means for electro-magnetically decoupling the AC magnetic field generated by an electrically conductive coil 192 from the top plate 180, bottom plate 156 and center post 158 by a cap 194 comprised of high electrical conductivity material. Additionally, power handling performance of the magnetic circuit can be improved by application of a magnetic fluid within the airgap 162.

The step 64 (seen in Figs. 4 and 6) holds and registers the second spring suspension disc 46 may be lowered to just slightly above flat 198, while still providing for axial displacement of the inner diameter 13 of the spring suspension disc 46 thus minimizing the height "H". This would assist in reducing the overall stack up height of the inertial type transducer 10 such that it may fit into restrained spaces.

Thus, the present invention has been described in an illustrative manner. It is to be understood that the terminology that has been used is intended to be in the nature of words of description rather than of limitation.

Many modifications and variations of the present invention are possible in light of the above teachings and examples of such variations have been provided which are not exhaustive. Therefore, within the scope of the appended claims, the present invention may be practiced otherwise than as specifically described.

Claims

What I claim is:

1. A suspension system for an inertial type acoustic transducer comprising: a) a magnetic circuit; b) a housing; and c) at least one sprung suspension disc comprising an inside edge, and at least one perforation for conducting convective air currents to cool the circuit and for allowing axial displacement of the inside edge.

2. The system of claim 1 wherein said transducer is associated with the inside edge of said sprung suspension disc thereby allowing axial movement of the magnetic circuit.

3. The system of claim 1 wherein said at least one perforation is radially positioned relative to said inside edge.

4. The system of claim 2 wherein said sprung suspension disc further comprises an outside edge, said outside edge associated with said housing.

5. The system of claim 4 wherein said housing comprises at least one ventilation opening for conducting convective air currents to cool the magnetic circuit.

6. The suspension system of claim 2 further comprising a bottom surface having a mounting disc.

7. The system of claim 6 further comprising a receiver apparatus wherein said mounting disc comprises means to align and affix the transducer to said receiver apparatus.

8. The system of claim 7 wherein said means to align and affix the transducer comprise at least one tab.

9. The system of claim 7 wherein said means to align an affix the transducer comprises a plurality of tabs and said receiver apparatus comprises a flat surface and a receiver portion said receiver portion comprising means for receiving and securing the mounting disc.

10. The system of claim 9 wherein said means for receiving and securing said mounting disc comprise a plurality of openings for receiving said plurality of tabs.

1 1. The system of claim 10 wherein said means for receiving and securing further comprises an inside surface of the receiving portion.

12. The system of claim 10 wherein each of said plurality of tabs is a helicoidal wedge and each of said plurality of openings for receiving said plurality of tabs comprises at least one mating sloped wedge to facilitate registering each of the helicoidal wedges upon partial rotation into said receiver apparatus.

13. The system of claim 9 wherein said means to align and affix further comprises at least one over center lock rib and said means for receiving further comprises at least one over center lock rib for locking the mounting disc and the receiver apparatus into position.

14. The system of claim 4 further comprising a second sprung suspension disc.

15. The systems of claim 14 further comprising locating means to affix said outer edge of a sprung suspension disc to said housing thereby effecting generally concentric alignment of the suspension disc and the magnetic circuit.

16. The system of claim 15 wherein said means to affix said outer edge of said sprung suspension disc comprises a groove on an inner surface of said housing.

17. The system of claim 4 wherein said magnetic circuit comprises: a) at least one magnet proximal to a voice coil associated with a coil former; b) an air gap; c) an output surface; and d) a magnetic field across said air gap wherein in response to electromagnetic force, said coil and coil former move within said air gap and against said output surface thereby transducing sound content.

18. The system of claim 1 wherein said magnetic circuit comprises a cup structure which is a unitary structure with said sprung suspension disc.

19. The system of claim 18 wherein said unitary structure further comprises a second sprung suspension disc and each of said at least one perforation is shaped and positioned radially in relation to said inside edge.

20. The system of claim 4 wherein said magnetic circuit comprises: a) at least one bottom plate with a center post having a first surface forming a proximal wall of an airgap; b) an anti-fringe groove between the base of the airgap and the bottom plate; c) at least one annular permanent magnet comprising an inner surface, a top surface, an outer surface, a bottom surface and a beveled surface wherein said bevel surface forms a conical taper; d) at least one top plate comprising a beveled interface coincident with the beveled surface of the permanent magnet; and e) a coil and coil former disposed at least partially in said air gap.

21. A suspension system for an inertial type acoustic transducer comprising: a) a magnetic circuit; b) a housing comprising at least one opening for conducting convective air currents to cool the circuit ; and c) at least one sprung suspension disc comprising an inside edge associated with the magnetic circuit for allowing axial displacement of the circuit.

22. The system of claim 21 wherein said sprung suspension disc further comprises an outside edge, said outside edge associated with said housing, and at least one opening for conducting convective air currents to cool the magnetic circuit and assist with said axial displacement.

23. The system of claim 22 further comprising a mounting disc and a receiver apparatus wherein said mounting disc comprises means to align and affix the transducer to said receiver apparatus.