US2630189A - Mounting of twin acoustic diaphragm assemblies - Google Patents

Description

March 3, 1953 J. JULIE 2,630,189

MOUNTING OF TWIN ACOUSTIC DIAPHRAGM ASSEMBLIES Filed NOV. 19, 1948 2 SHEETSSHEET l 1% 0 It; 13 I 9 INVENTOR. Joel Ju lie army - March 3,1953 J. JULIE 2,630,189

MOUNTING 0F TWIN ACOUSTIC DIAPHRAGM ASSEMBLIES Filed Nov. 19, 1948 2 SHEETSSHEET INVENTOR. c706] @116 AZ'Zome Patented Mar. 3, 1953 MOUNTING OF TWIN ACOUSTIC DIAPHRAGM ASSEMBLIES Joel Julie, New York, N. Y.

Application November 19, 1948, Serial No. 61,050

6 Claims.

' 1 This invention pertains to sound reproducing devices, and more particularly todirect acting diaphragms, flexible suspensions of diaphragms and mounting of diaphragm assemblies onto the loudspeaker chassis.

An object of this invention is to provide a loudspeaker of small size which would be capable of reproducing a wide range of audio frequencies with a degree of linearity and fidelity heretofore achieved only with large loudspeakers or duplex loudspeaker sytsems.

Another and more specific object of this invention is to devise a diaphragm which would be capable of reproducing the low frequencies without impairing its ability to reproduce the high frequencies.

A further object of this invention is to devise a diaphragm which would be capable of reproducing the high frequency range to the limit of audibility of the human ear.

A still further object of this invention is to devise a diaphragm which would have a high degree of linearity over the entire range of frequencies reproduced, in order to insure a maximum of fidelity of the reproduced sound.

Another and more specific object of this invention is to devise an improved diaphragm suspension in a loudspeaker characterized by a reduction of the suspension impedance, resulting in a lowered natural resonance frequency of a loudspeaker of a given size, without increasing the mass reactance of the moving parts.

A further object of this invention is to provide a suspension for direct acting diaphragms which would have a high degree of compliance toenable the diaphragm to vibrate at large amplitudes without causing amplitude distortion.

A still further object of this invention is to provide a flexible suspension for loudspeaker diaphragms having the above mentioned characteristics and yet requiring a minimum of space of the total diaphragm diameter, preferably this space requirement should approach zero in order to obtain a highest piston diameter utilization for a given size loudspeaker.

Another object of this invention is to provide a simple and efficient supporting member for the entire diaphragm and its associated parts, allowing easy subassembly of voice coil, diaphragm and flexible suspensions.

A further object of this invention is to provide a supporting member for the diaphragm and its associated voice coil and suspensions which would permit easy removal and replacement of the entire piston assembly, that is the diaphragm, susassembly.

pensions, voice coil and supporting member as a unit for the purpose of cleaning the annular air gap' or replacement of a damaged piston Another object of this invention is to provide a small size loudspeaker, capable of reproducing a wide range of frequencies with a high degree of fidelity, yet simple enough in construction and therefore inexpensive.

The above mentioned objects have been achieved in this invention by the use of a rigid dual or twin diaphragm formed in the general shape of a mushroom, consisting of a narrow angle center section conoid, having a high degree of rigidity for the purpose of efiicient reproduction of the high frequencies, which center section is coupled with a rigid conoidal section of relatively wide angle to make up the remainder of the diaphragm. The diaphragm is thus formed of two conical parts substantially equal in length, having their apexes in a common axis, with the apexes spaced from each other, and the intersection of the conoids intermediate said apexes, and in a plane at right angles to said axis. The smaller end of the central conoid is flexibly supported, and the larger end of the outer conoid is flexibly supported, whereby the entire diaphragm is free to move in the direction of its central axis. An improved outer edge flexible suspension of the diaphragm is obtained by using a reentrant type of suspension, which for practical purposes does away with the space limitation, which is usually a problem in the design of efficient outer edge suspensions. Preferably this improved suspension may be in the form of a corrugated disc joining the outer edge of the diaphragm with the support member; Furthermore, an improved support member is preferably made of a cup shaped body with suitable openings for the passage of sound. This improved support member is made removable, and ating to this invention;

Fig. 2 is a diagrammatic representation of the functioning of this invention;

Fig. 3 is a top view of the diaphragm as used in this invention, with half of the diaphragm cut away to expose the reentrant type suspension and the support for the assembly.

Figs. 4, 5, 6, '7, 8 and 9 are sectional views of other versions of the mushroom shaped diaphragms.

Similar characters of reference indicate corresponding parts throughout the various views.

The nature of the present inventions will be better understood by reviewing briefly the general behavior of direct acting diaphragms and the constructions of the prior art over which this invention is an improvement.

It is desirable that a direct acting diaphragm moves in a piston-like manner over a wide range of frequencies of the audio spectrum, without exhibiting any resonances, when actuated by the voice coil currents of the same frequency range. If a diaphragm is to act like a piston it has to be rigid enough in construction. On the other hand, for reasons of efficiency, .its mass has to be small. In view of these requirements, the most generally used types of diaphragms are made of paper, and to increase their rigidity they are formed in the shape of a cone. While various shapes of diaphragms have'been periodically suggested to improve their frequency range and reduce distortion, their application was confined mainly to large loudspeakers for reasons of cost considerations and space requirement. As a result the most accepted and probably the only type of small loudspeaker used to date makes use of a wide angle, cone shaped diaphragm, since it requires a .minimum of space and is inexpensive. Its limitations are obvious to those skilled in the art. They are capable of reproducing only a limited range of audio frequencies and also eX- hibit a number of other types of distortion the most objectionable of which is perhaps its nonlinearity, caused by resonances in the middle range of the audio spectrum.

The factors affecting its range can be analyzed as follows. While the low frequency limit of reproduced frequencies is a function of the baffle size, no bafile can extend the range of a loudspeaker much below its natural low frequency resonance. diaphragm is mass controlled, below the resonance frequency it is stiffness controlled and its efficiency falls off rapidly below the resonance frequency. The resistance of the suspension also causes distortion below the resonance frequency by clipping the peaks of the wave form. It seems therefore reasonable that a diaphragm should have as low a natural resonance frequency as possible and the resistance of the suspension should be as low as possible, if the loudspeaker is to have good low frequency response and fidelity.

There are two ways of lowering the resonance frequency of a diaphragm. One is to increase its mass and the other is to decrease the stiffness of the suspension.

While both of these methods can be used to lower the resonance frequency of a diaphragm the first method has the objectionable feature of reducing the response of the diaphragm at high frequencies, since for good high frequency response the diaphragm should be rigid as well as light. In the standard, wide angle, cone type diaphragm it is not feasible to increase the mass of the cone, as its high frequency response is bad Above the resonance frequency the enough. Any increase in mass of the wide angle diaphragm would only worsen its already poor response at high frequencies. This seemingly insurmountable problem has been successfully solved with this invention, by shaping the diaphragm in the general outline of a mushroom. The mushroom shaped diaphragm although higher in mass not only does not reduce the efficiency at high frequencies but even extends it to the limit of audibility of the human car by virtue of the very rigid construction of the center section of the diaphragm. In addition the mushroom shaped diaphragm also has the additional advantage of limiting the resonance peaks generally present in the middle frequency range of the standard type diaphragm. Summing up the mushroom shaped diaphragm has the advantage of lowering the natural resonance frequency of a diaphragm by virtue of higher mass, it has an extended high frequency response by virtue of rigid construction of the center section of the diaphragm, it has smooth response over the middle range, it can be shaped .to suit standard types of loudspeaker housings so that a minimum of retooling is required to adopt this diaphragm in a production process, it has a natural ability of preventing generation of subharmonies by virtue of its geometric construction, as will be readily recognized by those skilled in the art.

The above mentioned features are but a few of the more outstanding advantages of the mushroom shaped diaphragm.

While an increase in the mass of a diaphragm will lower the resonance frequency of the same, which method has been well applied in the con struction of the mushroom shaped diaphragm, increasing the mass to any appreciable extent in acoustic diaphragms is neither feasible nor advisable, as is well known to those skilled in the art. Therefore, the second method of lowering the resonance frequency, that of increasing the compliance of the suspension, should be made use of. Reducing the stiffness of the suspension is particularly advisable in small loudspeakers as the diaphragms of the latter have to be capable of rather large excursions in order to be able to generate an appreciable amount of acoustic power at low frequencies. Furthermore, from the point of view of fidelity, a highly compliant suspension will help reduce nonlinear distortion resulting from the nonlinear resistance of the suspension at large excursions of the diaphragm.

The diaphragm is suspended conventionally at two places: one is in the form of a corrugated disc at the voice coil, the other takes the shape of one or two corrugations inserted between the stiff part of the diaphragm and the loudspeaker chassis annular support. While both of these flexible suspensions add to the general stiffness of the suspension, the stiffness of the voice coil suspension can be readily controlled, as there is ample room to make the suspension as flexible and as capable of the large excursions of the voice coil as required.

Most of the remaining stiffness of the suspension that could not successfully be dealt with prior to this invention, is that contributed by the outer edge suspension.

The problem as it was viewed to this invention was to obtain a maximum flexibility of the outer edge suspension in a limited space between the stiffened portion of the diaphragm and the annular stationary support of the loudspeaker chassis in order to obtain a maximum effective piston diameter for a given size housing, the effective piston diameter being that of the stifiened portion of the diaphragm. Increasing the width of the flexible suspension of the outer edge of the diaphragm in an eifort to increase its compliance would decrease the effective piston diameter for a given size housing as well as introduce distortion as a result of the out-of-phase radiation from the suspension. Just how important the width occupied by the suspension becomes in the design of small loudspeakers will be emphasized by the following consideration: a loudspeaker with a nominal diameter of 4" has an outer suspension diameter of 3% and an eiTective piston diameter of 2%", i. e. a suspension width of only hardly enough for good flexible suspension, yet that suspension uses up almost 50% of the total area of the diaphragm (total diaphragm area-11 sq.

effective piston area-5.95 sq. in.)

It is therefore clear that in the design of small loudspeakers the width occupied by the suspension becomes of prime importance, and should be kept as narrow as is feasible for good compliance. This consideration has led to a variety of novel designs, all of them trying to squeeze in a maximum of flexibility into a minimum of space.

Let us consider first the presumably simplest method, that of thinning out the suspension, i. e. making the suspension a lot thinner than the rigid part of the diaphragm. This process not only has the disadvantage of being hard to control in production from the point of View of uniformity, but also results in a very flimsy suspension resulting in fracture of same either in production or after the loudspeaker has been in operation for a short period of time. Other arrangements proposed, making use of special materials for the suspension or come trick geometric designs have as a disadvantage either a costly process, or doubtful results or both, almost all of them incurably suffering from a lack of space.

A new approach to the problem is one of the main features of this invention. This as well as other features of this invention will be evident from the following description.

Fig. 1 is a sectional view of a loudspeaker incorporating some of the main features of this invention. A standard type housing 6 equipped with openings I? for the passage of sound is mounted in the conventional manner on the magnet frame 9. A standard type voice coil II is suspended in the annular air gap formed by the pole piece I2 and the circular opening in the magnet frame 9. Onto the voice coil is fastened the mushroom shaped diaphragm which according to this invention consists of a narrow angle, cone shaped, center section I and an inverted, backward folded, outwardly flared section 2. Section I and section 2 of the diaphragm can be fabricated separately and joined together as indicated in the drawing, or may be molded of one piece of material. The diaphragm may or may not be equipped with one or more compliances in the form of corrugations 3, depending upon the response desired. The voice coil centering within the annular magnetic air gap is accomplished in the conventional manner by a corrugated disc which is fastened onto the voice coil I! with its inner edge, its outer edge being fastened onto an annular shoulder of piston mechanism support I8. The outer edge of the diaphragm, in accordance with this invention, is not fastened to the housing 6 as is conventional, but there actually is a gap 5 between the outer edge of the diaphragm and the sealing ring 4 usually made of cardboard. The outer edge flexible suspension, according to this invention, is accomplished by a reentrant type annular disc 28, which is glued, cemented or otherwise fastened to the outer edge of the diaphragm on one side, the other side being fastened to the piston assembly support I8. The reentrant type flexible suspension 26 may be made of paper, cloth, impregnated cloth or any other material of flexible characteristics, and may take the form of a flat annular disc in the case a cloth or similar material is used or the annular disc may be equipped with corrugations as indicated in Fig. 2. The reentrant type annular suspension should preferably be made of porous material to permit proper sound radiation, however, it may sometimes be more advantageous to make that disc of fairly dense material if it is desired to dampen the low frequency resonance of the loudspeaker. The piston assembly support I8, another feature of this invention, can preferably be made in cup shaped form, having an annular flange I9 for fastening the reentrant type suspension and an annular shoulder I4 for fastening the voice coil flexible suspension and a flange I3 to insure proper mounting of the piston assembly with respect to the annular magnetic air gap. Support member It can be made removable from the loudspeaker housing and fastened onto it by means of centering screws iii. The support member 58 is equipped with large openings 8 which together with openings I? in the loudspeaker housing form a complete path for sound radiation from the rear of the loudspeaker. The voice current leads I5 should preferably be very light and very flexible and brought out at opposite ends. The soldering terminals I 6 for the voice leads should preferably be mounted on the support member I8 according to this invention in order to permit the removal of the entire piston assembly without disturbing any delicate elements of the assembly. In order to maintain the outer edge of the diaphragm in a plane perpendicular to the axis of motion of the piston and prevent wear of the diaphragm edge it may be advantageous to reenforce that edge. This is accomplished in this invention by a corrugation 22 and a flange 2 I, although other variations of edge reenforcement are possible. The bafiie board 23, outside of its usual purpose, also serves here to protect the protruding part of diaphragm I, 2.

This invention as pictured in Fig. 1, in addition to the advantages claimed for the mushroom shaped diaphragm as listed above, has also the following further advantages. It permits a maximum effective piston diameter for a given size loudspeaker chassis. The reentrant type outer edge suspension as used in this invention also makes possible to attain a degree of flexibility heretofore unattainable with other types of suspensions. This is due to the fact that the width of the suspension can be made as large as desirable, within limits of course, without affecting the effective piston diameter-in fact the effective piston diameter is actually thereby increased to a maximum possible. The air gap between the outer edge and the cardboard sealing ring has no appreciable effect on the performance of the loudspeaker as long as it is kept to a 1 s of an inch for 3 to 5 inch loudspeakers; a 6" loudspeaker can have an air gap as large as 1%". The advantages of a single support member for the entire piston assembly as used in this invention were already mentioned before. It should be pointed out that while one construction of such a support member is pictured in Fig. 1 other variations thereci'ar p ssi W h ntn piri of t is. in ent on 1 The improvement attained with this invention per Fig. 1 will be better appreciated from performance data obtained in samples. A 4" loudspeaker-having a diaphragm 3.5" in diameter yielded a low frequency resonance of 60 cycles. The high frequencies were extended in most samples to 20 kc., this frequency being down only 16 db as compared with the response of 1000 c. p. 5. Most samples showed no significant .peaks in the response.

, Fig. 2 is a diagrammatic sketch illustrating the functioning .of some of the main features of this invention. The diaphragm consists of a cone a. ir d n rrow allele cen r t o t n d p nnarily for the efiicient reproduction of high frequencies. The largeend of this conical center section is mechanically coupled with an inverted, outwardly flared diaphragm section 2. The magnitude of angle a is rather important as this angle determines not only the efficiency of reproduction at high frequencies, but also controls in large measure the linearity of response. There is an optimum angle for each grade of conematerial as well as its thickness. The diaphragm materials used in samples of this invention seemed to give best results with an angle a centering at about 75. The outer edge suspension-is accomplished by a reentrant type flexible suspension 20, i. e. a suspension which extends from the outer edge of the diaphragm toward the central axis of the loudspeaker. The diaphragm ran-d all parts attach-ed to it are supported by a single support Iii.

Fig. 3 shows a top view of the main features of this invention. The diaphragm, consisting of the narrow angle center section i and outer, backward folded, outwardly flared section 2 is equipped with a corrugation 22 andflange 2i for the purpose of .reenforcing the edge of the diaphragm. One half of the diaphragm has been cut away to expose underneath it the r-eentrant type flexible suspension 20 and the support mem, ber [8.

The mushroom shaped diaphragm can 'be made in a number of variations within the spirit of this invention. Some of these variations will be subsequently described with reference to the drawings.

Fig. 4 shows a mushroom shaped diaphragm having a narrow angle cone shaped center section 1 extending into a folded back (inverted) section 2, both being surfaces of revolution generated by straight lines, and an outer edge ree-nforcing corrugation 22. The two sections can be moulded or otherwise shaped separately or made of one continuous piece of material. Corrugations in the diaphragm may or may not be included, depending upon the response desired.

Fig. 5 shows a mushroom shaped diaphragm having a narrow angle center section I, an inverted inwardly flared outer section 2 and an outer edge reenforcing corrugation 22. Corrugations in the diaphragm may or may not be included depending upon the response desired.

Fig. 6 shows a mushroom shaped diaphragm having a narrow angle flared center section I and an inverted cone shaped outer section 2 and an outer edge reenforcing corrugation 22. The diaphragm can be made in two sections joined together, or fabricated of one piece of material. .Corrugations in the diaphragm may or may not be included depending upon the response desired.

Rig. ;'7 shows :a mushroom shaped .dianhl aem having a narrow angle flared center section -I. an inverted outwardly flared outer section 2 and an outer edge reenforcing corrugation 22. The diaphragm can be made in two sections joined or fabricated of one piece of material. Corrugationsv in the diaphragm may or may not be included depending upon the response desired.

Fig. 8 shows a mushroom shaped diaphragm having a narrow angle flared center section I, an inverted inwardly flared outer section 2, and an outer edge reenforcing corrugation 22. The diaphragm can be made in one continuous or two separate joined together sections. corrugations in this construction can be included but are hardly recommendable. I

Fig. 9 shows a mushroom shaped diaphragm having a narrow angle flared center section I, which flare is continuously increasing and finally inverting into section 2, the outer edge being provided with a corrugation 22 for reenforcement. This diaphragm is particularly suitable for very small loudspeakers. This form is based on the principle of the other embodiments (Figs. 4 to 8) 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 limited to the precise forms shown.

I claim:

1. In a twin acoustic diaphragm for a mass controlled sound reproducing device, the combination of an inner and outer conoidal rigid portion forming a single piston diaphragm surface extending from its perimeter inwardly, whose apexes point in opposite directions and are located on a common central axis some distance apart, the two conoids meeting in a plane perpendicular to said central axis at a distance intermediate between said apexes, said inner conoid having a narrow angle surface of revolution extending from its smaller end, and said outer conoid having a relatively wide angle surface of revolution, the diameter of the outer conoid base being substantially twice the diameter of the inner conoid base, the outer conoid base terminating in a perimeter having a circumferential surface which forms an angle with said central axis of the diaphragm, an annular flexible suspension having its outer end connected with said outer conoid base at its rear side and serving as the sole support for said outer conoid base, and yielding in the direction of said central axis and extending radially inwards of said outer conoid base, and means for fixedly supporting said suspension at its radially inward portion, at the exterior of the inner conoid acting as the sole support for the piston diaphragm including vents in said last named means providing the rear of said piston diaphragm with access of air from the front of said piston diaphragm, the outer conoid base and its connection with the outer end of the suspension being free from any air seal to enable the passage of air around the same in an unobstructed path from the front to the rear of said piston diaphragm, a sealing ring concentric with said outer conoid base connection with said suspension, and spaced radially outward therefrom, and a housing to support said sealing ring without supporting any part of said piston diaphragm, said housing being spaced from said piston diaphragm, and provided with vvents for'the passage of air therethrough whereby said unobstructed path of air from the front to the rear o said i to di hr is t d a ter S sound producing device is mounted in a completely enclosing battle, and said two-conoid piston diaphragm is free to move axially as an entity when actuated by a voice coil at said smaller end of said inner conoid.

2. The structure of claim 1, in which said inner conoid has a surface of revolution formed by a curved generatrix.

3. The structure of claim 1, in which said outer conoid has a surface of revolution formed by a curved generatrix.

4. The structure of claim 1, in which said circumferential perimeter of said outer conoid terminates in a free floating reinforcing flange for strengthening the perimeter of said outer conoid.

5. The structure of claim 1, in which said supporting means consists of a vertically disposed main rigid support, having an upper end and a lower end, and having sound radiation vents, and having said upper end connected with said radially inward portion of said annular flexible suspension of said outer conoid base, a voice coil support connected with the smallest perimeter of said inner conoid, and a second annular flexible suspension extending radially outwardly. from said voice coil support and connected with said lower end of said rigid support, said rigid diaphragm, voice coil, and said flexible suspensions being solely supported by said rigid support and said rigid diaphragm with said voice coil support being solely supported by said flexible suspensions, so that on the removal of said rigid support said rigid diaphragm with said voice coil support and said flexible suspensions form a self contained entity.

6. The structure of claim 1, in which said supporting means consists of a vertically disposed main rigid support, having an upper end and a lower end, and having sound radiation vents, and having said upper end connected with said radially inward portion of said annular flexible suspension of the outer conoid base, a voice coil support connected with the smallest perimeter of said inner conoid, and a second annular flexible suspension extending radially outwardly from said voice coil support and connected with said lower end of said rigid support, said rigid diaphragm, voice coil, and said flexible suspensions being solely supported by said rigid support and said rigid diaphragm with said voice coil support being solely supported by said flexible suspensions, so that on the removal of said rigid support said rigid diaphragm with said voice coil and said flexible suspensions form a self contained entity, a housing for said rigid support, and a centering means on said housing for said rigid support, whereby said entity may be centered in relation to said housing, and may be removed from said housing.

JOEL JULIE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,843,367 Langley Feb. 2, 1932 1,844,657 Hinckley et al. Feb. 9, 1932 1,844,802 lSeabert Feb. 9, 1932 1,984,550 Sandeman Dec. 18, 1934 2,186,576 Cornwell Jan. 9, 1940 2,269,284 Olson Jan. 6, 1942 2,329,560 Seabert Sept. 14, 1943 2,439,666 Marquis Apr. 13, 1948 2,490,466 Olson et al. Dec. 6, 1949

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