Loudspeaker Having Improved Diaphragm

Abstract

A loudspeaker assembly of a thin, compact, lightweight construction having a diaphragm which preferably is formed of cellular plastic material and provided with an integral marginal gasket. The diaphragm is mounted on a frame which is preferably formed of a solid body of the same or acoustically similar plastic material. The diaphragm has a concavo-convex form modified with acoustical materials and is capable of faithfully reproducing low frequency, midrange, and high frequency vibrations. The diaphragm is actuated by a voice coil mounted at the rear of the convex zone of the diaphragm, whereby the diaphragm and the magnetic assembly for actuating the same are constructed and arranged so as to provide an assembly which is not only relatively thin but may also present a labyrinth type of dust shield for the diaphragm actuating means. The frame further incorporates built-in centering and spacing tooling which is removed following manufacture.

Parent Case Text

RELATED APPLICATIONS

This application is a continuation in part of applicant's copending application Ser. No. 342,827 filed Feb. 5, 1964 and now U.S. Pat. No. 3,351,719 and Ser. No. 643,089 filed Jun. 22, 1967.

Description

FIELD OF THE INVENTION

The invention relates to loudspeaker assemblies of novel construction which are thin, light in weight, and acoustically designed to faithfully reproduce a wide range of sound vibrations.

DESCRIPTION OF THE PRIOR ART

Many types of loudspeaker assemblies have been heretofore designed but most constructions in current use embody conical diaphragms with a voice coil and magnetic assembly projecting rearwardly from the apex of the diaphragm, with the result that the assembly does not lend itself to the production of a thin flat assembly. Also, the conical designs because of opposing sound vectors provides an effective radiating area which is substantially smaller than the physical aperture. On the other hand those loudspeakers heretofore available which are provided with a relatively flat diaphragm have of necessity been of relatively large area and weight in order to permit even a limited reproduction of a broad band of frequencies.

A further problem presented by loudspeakers used in exposed area, or out of doors, and in automobile radios has developed by reason of the accumulation of dust and dirt in the air gap in which the voice coil is located whereby electrical and mechanical interference or damping of the voice coil develops so as to impair the operations of the loudspeaker.

Further, in the manufacture of loudspeakers accurate spacing tools and jigs are required to properly space diaphragms and voice coils in the structure, which adds to the cost and manufacturing difficulty.

SUMMARY OF THE INVENTION

In accordance with the present invention the foregoing objections and limitations of the prior art are reduced or eliminated by providing a loudspeaker assembly embodying a diaphragm and supporting frame of novel design and construction wherein the diaphragm is of a concavo-convex form modified by plastic acoustical materials and designed in such a fashion as to materially reduce the overall thickness of the assembly. The voice coil and magnetic assembly are then located at the rear of the convex zone of the diaphragm so as to further limit the thickness of the loudspeaker. Moreover, by forming the diaphragm of cellular plastic material it is possible to mold a marginal compressible gasket integral with the diaphragm for contact with the frame of the speaker so as to prevent or reduce any distortion of the frame or diaphragm in mounting the diaphragm on the frame. Such an integral gasket also eliminates the need for separate gasket to seal the speaker to its mounting.

The diaphragm also is formed with a ring or dust guard positioned to surround the magnetic elements and voice coil in a manner to present a labyrinth shield about these elements which reduces the danger of dust accumulation on the voice coil and in the air gap in which it is movable.

A further feature of the applicant's invention resides in the discovery of the fact that improved and more faithful reproduction of low frequency vibrations can be attained by forming radially extending slots or grooves in compliance zones adjacent the peripheral portions of the diaphragm and particularly at the corners of a rectangular diaphragm, and that such improvement is enhanced by filling such slots or grooves with a permanently compliant or elastic material.

An additional feature is the incorporation of spacing elements which are integral in the molding of the frame and which are removed after manufacture.

A further feature is a novel floating center element attached to the diaphragm which serves to eliminate resonant and antiresonant conditions at higher frequencies and thus provide a smooth response curve.

A further feature is the inclusion of tabs formed from compliant acoustical materials, located at the corners of the diaphragm and attached to the corners of the frame. These tiedown tabs serve to prevent low frequency breakup and to remove resonant and antiresonant excursions at the lower frequencies.

BRIEF DESCRIPTION OF THE DRAWING

FIG. - is a perspective illustrating a preferred form of sound-reproducing equipment embodying the present invention as seen from the front thereof;

FIG. 2 is a perspective showing the rear of the device shown in FIG. 1;

FIG. 3 is a vertical sectional view through the loudspeaker assembly shown in FIGS. 1 and 2 taken on the line 3-3 of FIG. 4;

FIG. 4 is a plan view of the diaphragm embodied in the assembly of FIGS. 1 and 2;

FIG. 5 is a plan view of the frame of the loudspeaker in the assembly of FIGS. 1 and 2; and

FIG. 6 is a transverse sectional view through one longitudinal edge of the diaphragm and frames taken on the line 6-6 of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In that form of the invention chosen for purposes of illustration in the FIGS. of the drawing, the diaphragm is indicated at 2 and is mounted on a frame 4 which is illustrated as being of a rectangular shape, although it may of course, be square, circular, bent out of the plane of the drawing, or of any other configuration. However, as shown, and in order to provide an assembly which is unusually thin and compact, the diaphragm 2 is preferably formed with a central zone or area 6 which is surrounded by a rearwardly and outwardly inclined surface 8 so as to render the central portion of the diaphragm generally convex. The outer portion or zone 10 of the diaphragm is inclined forwardly and outwardly from the inclined portion 8 of the diaphragm terminating in an edge 12 which is preferably located in substantially the same transverse plane as the outer face 14 of the convex central zone 6 of the diaphragm. The diaphragm thus has a concavo-convex configuration.

The portion of the diaphragm surrounding the edge 12 thereof may be relatively thin and formed with corrugations or grooves as shown at 16 to provide compliance zones about the periphery of the diaphragm proper to afford the desired freedom of movement of the diaphragm during operation. It has further been discovered that greater compliance and substantially improved low frequency response is attainable by providing diagonally extending slots or grooves 18 in the corrugations or peripheral compliance zones 16 of the diaphragm. Such grooves are of particular advantage when the diaphragm is rectangular in shape as illustrated and the slots 18 extend inward from the corners of the diaphragm through the compliance zones to the outer edge 12 of the diaphragm 2.

It has also been found in many instances that it is preferable to provide damping means in the form of compliance grooves or corrugations 16 having yieldable damping material 17, such as a silicone rubber composition therein. The grooves or corrugations 16 preferably extend along two opposite sides only of the diaphragm as shown in FIG. 4; whereas the two remaining sides of a rectangular diaphragm have no such damping or compliance means. Thus, as shown, when the diaphragm is of greater length than width, the longer sides may be provided with marginal strips or edge portions formed with the compliance means in the form of corrugations 16 having a damping means or composition therein as shown in FIG. 6. The shorter side or opposite ends of the diaphragm may then be flat and extend outward as shown in FIG. 3 into positions wherein the thickened gasket edge 22 of the diaphragm bears against the supporting surface 20 at the ends of the frame 4. When the diaphragm is thus formed the slotted corners thereof at opposite sides of the diagonal slots 18 are preferably secured to the frame by yieldable means such as compliant tabs or material indicated at 19. The construction thus provided serves to reduce or prevent low frequency breakup and to eliminate unwanted resonant and antiresonant excursions of the diaphragm at low frequencies. As a result the frequency response is smoothed out and more faithful sound reproduction is attained.

The diaphragm 2 may be formed of any suitable stiff, light weight vibratory material but is preferably formed of cellular material such as an expanded plastic composition of the type which may be produced by molding and expanding porous beads of polystyrene or the like. In molding or forming the diaphragm the portion which constitutes the peripheral compliance zones 16 is relatively thin as compared to the concavo-convex area of the diaphragm. The outer edge of the peripheral compliance zone 16 of the diaphragm may be cemented or otherwise secured to the forwardly facing surface 20 which extends inwardly from the outer marginal sides of the frame 4 of the assembly. Furthermore, in the preferred embodiment of the invention, the outer marginal portion of the diaphragm 2 is thickened as shown at 21 in FIG. 7 to provide an integral gasket between the diaphragm and the frame. This gasket is compressible so as to be reduced in thickness as shown by dotted line 21A of FIG. 7 upon the application of bolts or other securing means 24 at the corners or elsewhere. In this way it is possible to establish a firm air seal between the speaker and mounting structure without introducing strains or physical distortion in the speaker. As a result optimum acoustical performance is obtained without the need of external sealing or gasketing.

Another feature of the diaphragm is the inclusion of a ring structure of the same material, molded integral with the diaphragm. This ring fits around the magnet structure when assembled in the frame and serves to provide a long and sinuous path for dust or dirt to travel, thus protecting the structure from failure due to dust accumulating in the magnetic gap.

The central convex zone 6 of the diaphragm 2 is provided with a voice coil form 26 which projects rearwardly from the zone 6 so as to be located behind the convex zone. The voice coil form 26 is cemented or otherwise secured to the central portion of the zone 6 and for ease in assembly the diaphragm may be formed or molded with a central opening 28 therein providing for insertion and a close fit between the voice coil form and the inner surface of the opening 28. Cement, glue or other means 30 may be employed to secure the outer end of the voice coil form 26 to the inner surfaces of the central opening 28 so as to fixedly bond and position the voice coil form in place. The voice coil 32 is wound upon the voice coil form 26 and by reason of the fact that the central zone 6 of the diaphragm is convex, the voice coil 32 is actually positioned in a plane which is substantially parallel to the plane of the inner surface of the outer portion or zone 10 of the diaphragm. Thus, the total depth of the diaphragm and its voice coil assembly is substantially no greater than the total depth of the concavo-convex diaphragm itself.

In order to complete the diaphragm and provide the desired piston surface for most effective propagation of sound waves thereby, the outer end of the voice coil form 26 is closed by an insert 34. The insert preferably is of the same thickness, composition and density as the surrounding convex zone 6 of the diaphragm and is secured to the inner surface of the voice coil form in the plane of the outer surface of the zone 6 by means of acoustical material such as a silicone rubber composition which serves both as an adhesive and to independently suspend and at least partially decouple the insert 34 from the surrounding portions of the diaphragm. It has been found that the damping effect of a properly chosen acoustical material serves to cause acoustical vibrations which would normally traverse the center of the diaphragm to be damped out thus reducing distortion and improving the frequency response.

The frame 4 of the assembly illustrated is formed of a material having compatible physical and acoustical properties serving to limit the disparity in acoustical properties at the junction or joint between the diaphragm and frame. For this purpose the frame may be formed of an injection molded plastic material, such as unexpanded polystyrene, for example, having physical and acoustical properties which are the same or similar to those of the cellular or expanded polystyrene diaphragm itself.

As shown most clearly in FIG. 3 of the drawings, the frame 4 has relatively narrow sides 40 and 42 and similar relatively narrow ends 44 and 46 defining a rectangular outer frame with the forwardly facing diaphragm-supporting seat or surface 22 which projects inwardly from an outer marginal diaphragm-positioning rim 48. The sides and ends of the frame 4 are stiffened and maintained in a common plane by means of the upward and downward extension of the rim 48 with respect to the diaphragm-supporting surface 22 and by means of a further downwardly and inwardly extending reinforcing rib 50 which extends parallel to the downwardly projecting portion 48A of the diaphragm-positioning rim 48.

The magnetic assembly 52 which serves to actuate the diaphragm 2 of the loudspeaker is supported by the web 54 consisting of arms 56 which extend inwardly from the marginal frame at suitable points and preferably extend inward from the corners of the frame to a magnetic assembly supporting ring 58. The ring 58 is preferably formed integral with the arms 56 and marginal frame numbers 40, 42, 44 and 46 as a portion of a molded unitary body.

The ring 58 presents a lower inwardly projecting flange 60 and an outer upwardly extending annular rim 62. The magnetic assembly which cooperates with the voice coil 32 to actuate the diaphragm preferably embodies a ring-shaped permanent magnet 64 which fits closely within the annular rim 62 and rests upon the inwardly projecting flange 60 of the ring 58 of the frame number. An annular bottom plate 66 formed of ferromagnetic material fits with the flange 60 of ring 58 and has a central pole piece 68 mounted thereon and projecting upward within the voice coil form 26. A top plate 70 formed of ferromagnetic material is located above the permanent magnet 64 and projects inwardly therefrom to cooperate with the pole piece 68 to present an air gap 72 of limited cross section within which the voice coil 32 on the voice coil form 26 is freely movable.

As shown in FIG. 3 of the drawings, the upper extremity 74 of the annular rim 62 of the ring 58 is preferably reduced in thickness and is turned inwardly over the upper face of the permanent magnet 64 and toward the outer edge of the top plate 70 to hold the magnetic assembly securely in place within the ring 58 of the frame. Such inward folding or spinning of the extremity 74 can be effected by means of a heated tool or the application of a volatile solvent or the like thereto so as to establish a fixed and permanent mounting of the magnetic assembly in the ring 58 of the frame and in a predetermined and immovable relation with respect to the voice coil 32 carried by the diaphragm 2.

In order to supply diaphragm actuating current to the voice coil 32 the diaphragm 2 is preferably provided with grooves 80 in which the electrical leads 82 connected to the voice coil are located. The leads 82 are preferably embedded in a compliant plastic material which substantially fills the grooves 80 and serves to hold the leads 82 in place preventing vibration or displacement thereof. The outer ends of the leads 82 are connected to a terminal block 84 mounted in or on the side member 42 of the frame 2 for connection with a suitable source of energizing current. As shown the terminal block 84 is preferably received and retained in place on the frame by means of a locating pin 86 and a positioning web 88 so as to enable the terminal block to be snapped into place assuring proper location and retention thereof.

When the various elements of the assembly are constructed as herein described, the diaphragm 2 may be placed in position with integral marginal gasket 21 of the diaphragm resting upon the inwardly facing supporting surfaces 22 of the side and end members 40, 42, 44 and 46 of the frame 4. The compressible gasket 21 of the diaphragm is preferably cemented in place on the surface 22 of the diaphragm of the frame and the frame and gasket are bolted, clamped or otherwise secured together by securing means. Such securing means may extend through the mounting holes 24 passing through the gasket 21. In this way gasket 21 is compressed and the diaphragm and frame securely fastened together with the voice coil 32 carried by the diaphragm accurately positioned within the air gap 72 of the magnetic assembly. Moreover, in order to assure the most accurate and uniform assembly of the diaphragm and frame, the frame 4, as initially molded, is provided with spacing elements 73 which serve to assure proper registration and spacing of the frame and diaphragm until the cement between the gasket and surface 20 has hardened. The spacing elements 73 can then be broken off or removed to permit the diaphragm to vibrate properly.

An important feature of the present invention resides in the provision of means to shield the voice coil, air gap and associated elements from the adverse effects of dust accumulations which might impair the operation of the loudspeaker, the central convex zone 6 of the diaphragm is provided with a rearwardly extending annular ring 90 which preferably is formed integral with the diaphragm and surrounds the top plate 70 or other portions of the magnetic assembly so as to cooperate with the ring 58 of the frame to present a labyrinth barrier between the voice coil and air gap of the diaphragm actuating means and the exterior of the assembly. In this way the entry of dust and dirt into contact with the relatively movable elements of the diaphragm actuating means is precluded and the equipment may be used in automobiles and elsewhere under adverse conditions which would tend to impair or interfere with the most effective and faithful operation and sound reproduction by the loudspeaker. The annular ring 90 preferably is located in alignment with the outer edge of the central zone 6 of the diaphragm 2 so as to cooperate therewith in establishing a relatively high frequency vibratory area in the diaphragm. At the same time the diaphragm is provided with yieldable damping material on the inner surface thereof and about the annular ring 90, as shown at 92 and 94, whereby a smoother frequency response is attained and resonant and antiresonant responses are reduced.

The sound-reproducing equipment produced in accordance with the present invention and described above is unique in that the overall thickness of the assembly may be substantially less than 1 inch, whereas the tone qualities, volume and range of frequencies which can be faithfully reproduced is substantially equal to that attainable heretofore by the use of much larger, heavier and far more bulky equipment. Furthermore the assembly can be produced very economically and lends itself to many uses and applications which have precluded the use of small, thin, light weight loudspeakers and sound reproducing equipment heretofore.

Although the embodiment of the invention shown in the drawings and described above represents one particular and preferred form of the invention which has proven very successful in operation, it will be apparent that numerous changes and modifications in the form, construction and arrangement of the elements of the combination may be made. In view thereof it should be understood that the particular form of the invention disclosed herein is intended to be illustrative only and is not intended to limit the scope of the invention.

Claims

I claim:

1. A relatively thin flat loudspeaker assembly comprising a frame, a diaphragm having a central flat zone surrounded by an inclined connecting surface extending from said central zone to an outer sound-reproducing zone of the diaphragm which is inclined oppositely to said connecting surface, compliance grooves in the diaphragm between said outer zone and marginal edges of the diaphragm, the marginal edges of the diaphragm being connected to said frame and lying in substantially the same plane as the central zone of the diaphragm, a voice coil connected to the central flat zone of the diaphragm near the midportion thereof, and a magnetic assembly supported by said frame and located adjacent said voice coil for actuating said diaphragm.

2. Sound-reproducing equipment as defined in claim 1 wherein the central flat zone of the diaphragm has an annular reinforcing rib extending rearwardly from the marginal portions thereof into a position surrounding the magnetic assembly and serving as a dust guard establishing a labyrinth passage between said rib and the magnetic assembly.

3. Sound-reproducing equipment as defined in claim 1 wherein the frame and diaphragm are substantially rectangular in shape and said compliance grooves extend parallel to the longitudinal edges only of said diaphragm.

4. Sound-reproducing equipment as defined by claim 1 wherein the diaphragm is formed with compliance means adjacent the marginal edges thereof, said compliance means being provided with slots therein extending inward from edges of the diaphragm toward said voice coil.

5. Sound-reproducing equipment as defined in claim 1 wherein said frame and diaphragm are generally rectangular in shape, compliance means in the form of corrugations are formed in said diaphragm adjacent the marginal edges of the diaphragm, and slots are formed in said corrugations and extend diagonally inward from edges of the diaphragm near the corners of said diaphragm.

6. Sound-reproducing equipment as defined in claim 1 wherein said diaphragm is formed of stiff, cellular plastic material and the marginal edges of the diaphragm are provided with an integral compressible gasket consisting of a thickened marginal rim of said cellular plastic material.

7. Sound-reproducing equipment as defined in claim 1 comprising a diaphragm formed of cellular plastic material, a frame formed of a solid body of plastic material, the marginal edges of said diaphragm being supported by said frame, and means carried by said frame for actuating said diaphragm.

8. Sound-reproducing equipment as defined in claim 7 wherein the diaphragm and frame are formed of plastic material having essentially the same composition.

9. Sound-reproducing equipment as defined in claim 7 wherein said diaphragm has a central portion presenting a convex surface lying in substantially the same plane as the marginal edges of the diaphragm and surrounded by a portion of said diaphragm presenting a concave surface, a voice coil mounted on a voice coil form connected to said central portion of the diaphragm and projecting from the concave side thereof, a magnetic assembly surrounding said voice coil, said frame having a ring in which said magnetic assembly is mounted and arms extending from said ring to said frame.

10. A sound-reproducing device as defined in claim 1 wherein said diaphragm is formed of cellular plastic material and said frame is formed of a solid body of plastic material.

11. A sound-reproducing device as defined in claim 1 wherein the central portion of the diaphragm is provided with an insert secured about its edges to the surrounding portions of the diaphragm by compliant damping material.

12. A sound-reproducing device as defined in claim 1 wherein the central portion of the diaphragm is at least partially decoupled from the remaining portions of the diaphragm.

13. A sound-reproducing device as defined in claim 3 wherein the diaphragm is provided with slots extending diagonally inward from the corners thereof and the portions of the diaphragm at opposite sides of said slots are secured to the frame by yieldable means.

14. A sound-reproducing device as defined in claim 1 wherein the frame is provided with removable positioning elements for assuring accurate location of the diaphragm with respect to the frame.