US3019849A

US3019849A - Loudspeaker diaphragm suspension

Info

Publication number: US3019849A
Application number: US827607A
Authority: US
Inventors: John A King
Original assignee: General Dynamics Corp
Current assignee: General Dynamics Corp
Priority date: 1959-07-16
Filing date: 1959-07-16
Publication date: 1962-02-06
Anticipated expiration: 1979-02-06

Description

Feb. 6, 1962 J. A. KING 3,019,849 LOUDSPEAKER DIAPHRAGM SUSPENSION Filed July 16, 1959 3 Sheets-Sheet 1 PRIOR ART INVENTOR. JOHN A. KING BY wqsaw gy ATTORNEY Feb. 6, 1962 J. A. KING 3,019,849

LOUDSPEAKER DIAPHRAGM SUSPENSION Filed July 16, 1959 3 Sheets-Sheet 2 F5. 3 ll 722 I INVENTOR.

JOHN A KING ATTORNEY Feb. 6, 1962 J. A. KING 3,019,849

LOUDSPEAKER DIAPHRAGM SUSPENSION Filed July 16, 1959 5 SheetsSheet 3 INVENTOR.

JOHN A.. KING ATTORNEY United States Patent- O 3,019,849 LOUDSPEAKER DIAPHRAGM SUSPENSION John A. King, Rochester, N.Y., assignor to General Dy- I namics Corporation, Rochester, N.Y., a corporation of Delaware 7 A Filed July 16, 1959, Ser. No. 827,607 13 Claims. (Cl. 181-31) This invention relates to sound reproducing devices, and more particularly to a suspension system for loudspeaker diaphragms.

Considerable effort has been spent in the loudspeaker field to increase the power handling capacity of small speakers without correspondingly increasing the distortion introduced due to the suspension system. This effort has become even more pronounced in recent years due to the trend, in the high fidelity home equipment field, towards smaller speaker systems having higher power handling capabilities. This trend is also present in the high intensity sound field where his desirable to maximize the acoustic power radiated from a given transducer while minimizing the frontal area of'the transducer.

Various suspension systems have been designed in an attempt toincrease the power handling capabilities of loudspeakers. Some of these efforts have been directed towards allowing greater cone excursions thus increasing the radiated power. Examples of such prior art systems are disclosed in the patents of Marquis, 2,439,666, issued April 13, 1948, and Olson et al., 2,490,466, issued December 6, 1949. The Marquis and Olson patents both disclose loudspeaker suspension systems utilizing a plurality of serially connected compliant elements wherein the compliant elements consist of circumferentially corrugated ring members one of which is attached to the dia phragm and the other of which is attached to the diaphragm supporting member. increasing the allowable cone excursions but, on the other hand, the corrugations of the suspension system encroach upon the nominal diaphragm area thus limiting the frontal area available for radiating acoustic power. In such systems, any attempt to further increase the allowable amplitude of diaphragm excursion by increasing the number of circumferential corrugations present in a compliant element would result in further encroachment upon the area remaining for the diaphragm.

It is thus desirable to have a suspension system for a loudspeaker diaphragm which provides for increased axial motion for. the diaphragm without encroaching upon the frontal area available for the diaphragm.

It is, therefore, an object of my invention to provide an improved diaphragm suspension system for a loudspeaker.

It is a further object ofmy invention to provide an improved diaphragm suspension system which increases the power handling capacity of speakers having a given frontal area.

It is another object of my invention to provide an improved diaphragm suspension systernwhich allows an increased motionof the diaphragm and also has provisions for the accommodation of a diaphragm having larger nominal diameters.

It is a further object of my invention to provide an improved bellows type suspension system in which the opposed ends of the bellows are secured to the supporting frame.

i In accordance with my invention, I provide a compliant seal element in the form of a generally cylindrical bellows or corrugated element the ends of which terminate at suitable surfaces on the loudspeaker basket while the periphery of the radiating diaphragm is secured to its center corrugation. Thus, in accordance with my invention, a loudspeaker diaphragm suspension element is pro- Such systems are useful in 3,019,849 Patented Feb. 6, 1962 vided which, when used in conjunction with a loudspeaker surface of the diaphragm vibrate in velocity phase with the driving force (assuming a linear driving force on the diaphragm), is a function of both the area and the displacement of the radiating diaphragm, these parameters should be made as large as possible if the acoustical power output is to be maximized. Thus, for a given over-all basket size the only way to maximize both of these parameters simultaneously is to utilize a suspension which permits maximum diaphragm area coupled with maximum excursion capabilities, consistent with a mechanical stability of the moving system.

Heretofore attempts have been made to utilize bellows type of suspension systems in order to increase the cone excursion capabilities of loudspeaker diaphragms, However, such systems displayed a nonsymmetrical or rectifying action since the forces required to move the diaphragm a given distance from zero position, in each direction, were not equal. This inequality in the force versus displacement ratios, depending upon the direction of movement of the diaphragm, arose due to the manner in which the bellows interconnected the supporting frame and the diaphragm. Since one end of the bellows was supported by the basket and the other Was connected to the diaphragm, the bellows would be in tension when the diaphragm was driven in one direction and conversely it would be in compression when it was driven in the opposite direction. It has been found that the application of equal forces in opposite directions in such suspension systems does not result in equal and opposite displacemerits and consequently, the so-called rectifying action has been found in such suspension systems. Thus, since a speaker is stiifness-controlled below its resonant frequency, this nonlinearity due to the nonsymmetrical na-' ture of such suspension systems introduced substantial harmonic distortion in the low frequency range. This nonsymmetrical effect is not present in the suspension system of my invention due to the symmetrical manner in which the bellows element couples the diaphragm to the loud speaker frame.

It is a further feature of my invention that the bellows suspension element is damped to the extent necessary to minimize resonant effects at the low frequencies by cementing strips of cellular or foam type plastic at intervals to the surface of the bellows.

It ia further feature of my invention that thecompliant bellows element not only maximizes the acoustic radiative power by allowing large cone excursions coupled with large radiating surfaces but it also lowers the. natural resonant frequency of the moving system and hence materially extends the low frequency end of the audible range of reproduction. This is accomplished by the bellows element, due to its high compliance, without increasing,

the mass of the moving system which would be deleterious to the high frequency response of the system.

These, as well as other features of the invention, will become apparent from the following description with comprising a diaphragm 1 having a voice coil former 2' cemented to the small end thereof. Coil former 2 carries voice coil 3 within annular'air gap 23. Coil former 2 is supported for vibration'in an axial direction within air gap 24 by compliant membersA- and 6. Member 4' is secured to basket 7ofthe loudspeaker and to the point at which coil former 2 joins diaphragm 1. Compliant member 4 provides means for supporting voice coil 3 for axial movement within the'air gap while limiting the radial motion of the coil within the air gap. Thus, merrl her 4 is designed tohave very high'late'ral stiifness'while being highly compliant in an axial direction. Compliant member 4' does not encroachupon' the radiating area necessary to accommodate diaphragm 1 and it is not,"- therefore, necessary to utilize a bellows type suspension. A normal compliant element can be used as long as it provides a sufiicient number of corrugations so' as to match the excursion capabilities of corrugated compliant element 6. The base of diaphragm 1 terminates in integral supportrim 5' (see FIG. 5) which extends radially outward from the base and is cemented to bellows 6 in the trough 18 f the center corrugation (see FIG. The outer peripheral edge of rim 5 is flexiblysupp'orted by fibrous,-compliant element 6 which is attached to basket'7 at tiange's'S and 9; Ends 10 and 11 of bellows flare respectively attached to flanges 8 and 9 by annular rings 12 and 13 (see FIGS. 3a, 3b and 3c).

Provisions are made formounti'ng the loudspeaker in an opening in baffle 16 by securing fiange ls as-indicated at 17, to baffle 16.

Referring now to FIG. 2, a conventional' prior art loudspeaker is illustrated as an aid in describing the features Dimensions A, B and C, utilized in of this invention. FIGS. 1 and 2, are representative of various frontal areas of prior art speakers and speakers of my invention. Dimension A is proportioned to the area ofbaffie 16 necessary to accommodate the speaker. Dimension B represents the area available for the suspension system and diaphragm within the confines of the basket. Dimension C represents the'net area available for a diaphragm. Assuming, for explanatory purposes, that dimensions A, B and C of the loudspeaker of FIG. 1 are equal to the corresponding dimensions of the prior art speaker of FIG. 2, it will be noted that dimension D of FIG. 1, which represents the total excursion capabilities of diaphragm 1, issignificantly greater thandistance D of the prior art speaker of FIG. 2. Therefore, assuming that both speakers have the same radiating area, the speaker of FIG. 1 will have a correspondinglylarger acoustic power output rating over a wider range of frequencies.

Referring now to FIGS. 1, 3a, 3b, 3c and 3d, provisions are made for supporting ends 10 and 11 of bellows 6, respectively, from the inner edge of supporting

rings

12 and 13. In FIG. 30!, it is noted'that' rim 5 of diaphragm 1 is Secured to bellows 6 in trough 18 of center corrugation. Since the points of termination of edges 10 and 11 of the bellows and the point that the bellows will be acted upon by diaphragm 1 are in alignment, there will be no force couples set up in the suspension system. In FIG. 3b, the forces exerted by diaphragm upon bellows 6 in trough 19 are not in alignment with the points at which bellows 6 terminate upon ringslZ and 13. Consequently, forces will be set up about the points where diaphragm 1 joins bellows 6. These forces will tend to disturb the axial alignment of voice coil 3 within the air gap and, at the same time, will tend to introduce additional nonlinearity into the suspension system. However, it is noted that the suspension system of FIG. 3b has the advantage that it does not protrude beyond the inner edge of supporting

rings

12 and 13 and consequently does not encroach upon the area within the inner diameter of the supportingrings that would otherwise be-available for accommodating a sound radiating diaphragm. One of the advantages common to the embodiments of FIGS. 3:: and 3b is that it is mechani' cally easier to secure rim 5 of diaphragm 1 to bellows 6 in the trough of a" corrugation such as,

troughs

18 or 19 rather than securing it to the peak of a corrugation Referring to FIG; 30, the structure shown here is hasically similar toth'at'o f FIG. 3b"in that bellows 6 is recessed within the space between

rings

12 and 13. FIG.- 30 differs from theeinbodiment of FIG. 3b in that it has "an even nu'mber of coniplete'corrugations and consequently "diaphragm 1 in order tit-be secured to' the ecu-- ter'of the bellows,'issecured to peak 20 of the center corrugation. Sincebellows d ot-H6135 has 'an odd' numberof complete-corrugationsdiaphragm 1 can 'be se-- cured todhe bellowsin trough19 which is midway between ends lfland-ll of the bellows The arrangementof FIG." 3c results thealignment of the three points at which forces are-applied to bellows -6.

Referring'toFIG, 3d, Ihaveshown an arrangement whereiri thecompliant bellows element 6 is provided with corrugations'ofg'a'greater amplitude than those of the embodimentsof PIGS. 3a, 3band 30, while} at the same-time, thenumberof' corrugations is reduced. One' complete corrugation is provided each side 4 of the center of the bellows element; thus te'ndingto minimize'the problem- 0f resonances in thesuspension system. This arrangement'alsotendsto minimizepile-up of the corrugations when diaphragm 1 is'at, or approaching,-thelimits of excursion. nonlinearity and also tends to producea'slapping action between adjacentsurfac'es of the bellows when the suspension system resonates! Diaphragm 1 in FIG. 3d is secured to bellows 6 in the troughof 'co'rrugation'22 which is in alignment with the pointsat which bellows 6terminate'upon'rings'12 and 13; Thus, the embodiment of FIG. 3d'hasthe' advantagethat'the three points of termination are not only in"alignm'ent but-the number of corrugations are minimized, thus reducing resonance and pile-up problems.

The exact form that bellows 6 will take and the manner in which it is secured to the supporting rings and diaphragm will, of course, depend upon the materials used, the excursion desired and the other parameters of the speaker. However, usually it is desirable to minimize the number of corrugations-and thus minimize the attendant resonance problems Generally, it is desirable to have only one or two complete corrugations on each side of the midpoint of the bellows.

The exact configuration'of the bellows" will be" determined by setting thedistance' between the ends of the bellows equal tothemaximum cone excursions'desired and then, knowing the material and its elastic properties, the depth of the'corrugation has to be'such as-to allow the maximum desired cone excursion before the nonlinearity of the "suspension system becomes significant.

This point varies in accordance with the material used but it is generally of the order of degrees.

The spacing between bellows 6 and supporting frame-7, as illustrated in FIG; 1, has beenemphasized for convenience of illustration but it is recognizedthat the bellows would be placed as close as possible to the supporting structure withoutoccasioning any interference between the bellows and basket.

Referring to FIGS. 4 and 5,, a method of damping the bellows suspension of the invention is illustrated. Resonance of the suspension system is primarily due to the distributed mass and compliance of the corrugations and is present whether the suspension system utilizes a normal Such pile-up introduces additional system having circumferential corrugations or whether a bellows type suspension is utilized. In both situations, it is necessary to damp the system to a point where the resonant condition will not be objectionable when the speaker is used within its rated power handling capacity. Damping is provided by attaching strips 23 of resilient or Semi-resilient plastic or open or closed cell structure over the surface of the bellows, perpendicular to the corrugations. As seen in FIG. 5, damping strips 23 are applied over the interior and the exterior surface of bellows 6. The amount of damping can be controlled by varying the thickness and/ or the spacing or the strips.

It will be apparent to those skilled in the art that other arrangements and combinations within the spirit of the invention are possible. It is not intended, therefore, that the invention should be limitedtto the precise modifications shown.

I claim as my invention: 1

1. In a sound-reproducing device, an acoustic dia phragm, a housing having first and second supporting flanges lying in spaced parallel planes, a generally cylindrical corrugated compliant element, means forrigidly attaching the opposed ends of said compliant elementto said first and second supporting flanges and means for attaching said diaphragm to the interior surface of said cylindrical element intermediate said ends. I V

2. The combination of claim 1 in which said attaching means lies in a third plane parallel to said spaced parallel planes.

3. In a sound-reproducing device, an acoustic diaphragm, a housing having first and second supporting flanges lying in spaced parallel planes, a generally cylindrical corrugated compliant element, means for rigidly attaching the opposed ends of said compliant element to said first and second supporting flanges and means for attaching said diaphragm to the interior surface of said cylindrical element at points which lie in a third plane, said third plane being parallel to and equally spaced from said spaced parallel planes.

4. Ina sound-reproducing device, a generally conical diaphragm having a base lying in a plane perpendicular is interposed between said first and second planes.

5. The combination of claim 4 in which each of said first and second supporting means includes an annular'ring of rigid material which is secured to the corresponding one of said supporting flanges.

6. The combination of claim 5 in which each of said first and second supporting means further includes means for securing said annular ring to the corresponding end of said bellows element.

7. In a sound-reproducing device, an acoustic diaphragm, a housing having first and second supporting flan es lying in spaced parallel planes, a generally cylindrical corrugated compliant element, means for rigidly attaching the opposed ends of said compliant element to said first and second supporting flanges, means for attaching said diaphragm to the interior of said cylindrical element, said diaphragm attaching means lying in a third plane parallel to said spaced parallel planes and equidistant from said spaced planes, and means for damping said compliant element.

8. The combination of claim 7 in which said damping means includes strips of resilient material secured to the surface of said corrugated element and generally parallel to the axis of said compliant element whereby said damping means also prevents the surfaces of adjacent corrugations of said compliant element from coming into contact with each other.

9. The combination of claim 8 in which said strips of resilient material are secured to both the inner and outer surface of said compliant element.

, 10. The combination of claim 4 in which said first and second supporting means and said attaching means intersect the surface of said compliant element at points which are equidistant from the axis of said compliant element in any given radial direction.

11. The combination of claim 10 in which said compliant element is symmetrical about said third plane whereby the rectifying type of distortion is cancelled.

12. The combination of claim 4 in which said compliant element has an odd number of corrugations between said one end and said other end and said third plane intersects said compliant element in the trough of a corrugation.

13. The combination of claim 4 in which said compliant element has an even number of corrugations between said one end and said other end and said third plane intersects said compliant element on the peak of a 2,815,823 Olson et al. Dec, 10, 1957