US2302178A

US2302178A - Acoustic diaphragm

Info

Publication number: US2302178A
Application number: US365916A
Authority: US
Inventors: Joseph B Brennan
Original assignee: Individual
Current assignee: Individual
Priority date: 1940-11-12
Filing date: 1940-11-12
Publication date: 1942-11-17
Anticipated expiration: 1959-11-17

Description

4 J. B. BRENNAN ,30

ACOUSTIC DIAPHRAGM Filed Nov. 12[ 1940 2 Sheets-Sheet 1 INVENTOR. JOSEPH F. BEEN/VA N 1942- J. B. BRENNAN ACOUSTIC DIAPHRAGM Filed Nov. 12, 1940 2 Sheets-Sheet 2 IN VENTOR. JOSEPH .B- .BPf/VA/A/V YWW Patented Nov. 17, 1942 U i. E iii i K 5 r, r Sosepn rs.

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1? (Claims. ($1. l ttl -$355) This invention relates to acoustic diaphragrns such are used in. radio receivers, public ad dress systems and the like. Insofar as common subject matter is concerned, this application con-- stitutes a continuation in part of copending applications Serial No. 1215M, filed January 21, 1937, and Serial No. 351,791, filed August 8, 1940.

A diaphragm of this type ordinarily comprises a generally conical or conoidal portion which is provided at its smaller end with a cylindrical nect: to which a moving voice coil is secured. This coil is disposed in a magnetic field and voice currents flowing through the coil result in vibration of the cone. At its larger end the cone is provided with a generally radially extending flange which is clamped or otherwise secured to a support and which functions as a support for the cone. The cones preferably are made of fibrous material deposited on a form and, in orde to secure different characteristics of the cones, the material may be impregnated with various substances such as lacquers, latex and various plastics.

The outer rim of the cone which functions to support the cone has little, if any function so far as the production of sound is concerned, but unless the flange or rim is properly constructed, it may adversely affect the performance of the cone or diaphragm. Thus, the stillness and inertia of the rim affect the natural period of vibration of the diaphragm, and the rim further functions as a part of the usual baflle which is employed to improve the efficiency and acoustical characteristics of the device. I

In order to produce a flexible connection between the conical part of the radial extending flange, it has been the practice to provide the radial extending flanges of cones with circumferential corrugations. It has also been proposed to make the connecting portion between the conical portion and the radial extending flange of lesser thickness than the conical portion or the flange. Both of these constructions have met with some success but neither construction has given completely satisfactory results for the radial corrugations do not sufllciently increase the flexibility I for all purposes and the thinning of the material cannot be carried out with sufllcient accuracy to produce in quantity cones having identical characteristics and, further, a reduction in thickness throughout the circumference of the cone to a sufiicient extent to materially affect its characteristics may result in a serious weakening of the structure.

cones which the flexibility of the connection between the conical portion and the radial flange may be accurately controlled to produce cones having the desired characteristics while at the same time the acoustical properties and bathe effect are not sustantially impaired and the flange retains adequate strength to support the cones and accurately center them with respect to the frame of the loud speaker or other device. In order to accomplish this result, I preferably provide in the flange a sufficient number or" portions of suiflcient strength to properly support and center the cone while the remaining portions of the flange are weakened as by reducing the thickness or density of the material in these portions. Thus, for example, the supporting portions may be of the same thickness and strength as the material of the body of the cone, while the intermediate portions may be weakened so as to be of negligible structural strength so long as the weakened areas are such as to block the passage of sound from one side of the cone to the other to a. sufficient extent that the acoustical properties of the cone are not substantially impaired by the weakened areas. Or, depending upon the characteristics desired, the supporting portions may be of either greater or less thickness than the body of the cone so long as they have sufficient strength properly to support the diaphragm, while the intermediate portions are weakened.

In the drawings, in wluch I have illustrated various preferred forms of diaphragm embodying my invention, Fig. l is an elevation of one type of cone embodying my invention; Fig. 2 is a. section along the line 2-2 of Fig. 1; Fig. 3 is a rragmentary section through the rim portion of the cone as indicated by the line 3-3 of Fig. 1, the view somewhat diagrammatically illustrating the weakened portions of the rim or flange; Mg. 4 is a section similar to Fig. 3 out showing a modined construction insofar as the mode or increas-- ing the flexibility of the flange is concerned; Figs. 5 to 9, inclusive, are fragmentary elevations of diaphnagms embodying my invention and with modified forms of rim structures; Fig. 10 is an elevation showing my invention adapted to an elliptical diaphragm, and Fig. 11 is a fragmentary perspective view illustrating my invention applied to'a construction whereinthe supporting mange, while generally radial, has an intermediate cylindrical portion. Throughout the drawings, the thickness of the diaphragm is considerably exaggerated for convenience of illustration.

Referring particularly to Figs. 1 and 2, a dia- According to my present invention, I provide 55 phragm made according to my invention may comprise a generally conical body portion Ill having at the small end thereof a neck portion II to which the voice coil is secured and at its large end a generally radially extending flange l2, the peripheral edge of which is adapted to be clamped or otherwise secured to the frame of an acoustic device to assist in supporting the diaphragm. The conical portion l may be provided with a corrugation as indicated at I3, while the rim or flange l2 preferably is provided with a plurality of circumferentially extending corrugations H in order to increase the flexibility thereof in a manner well understood by those skilled in the art. Preferably the cone or diaphragm is of onepiece, seamless construction, being integrally formed by depositing fibrous material upon a base or mold having substantially the shape of the finished diaphragm. This may be accomplished in various ways understood by those skilled in the art, as by depositing the fibrous material from an aqueous suspension of the material onto a porous former or mold. The material may be pressed to make it more dense after being removed from the porous form and, if desired, may

be impregnated with various materials such as condensation products of urea and formaldehyde, phenolic condensation products, synthetic resins, lacquers, latex and other similar materials.

As heretofore stated, the sound output of the diaphragm and the natural period of vibration of the diaphragm depend to a considerable extent on the flexibility of the supporting rim or flange. Every movement or vibration of the diaphragm requires bending and distortion of the rim or flange. In order to control the stifiness of the rim, and preferably to reduce the stillness, thus reducing the natural period of vibration of the diaphragm and increasing the eiliciency of sound production thereby, I preferably form the diaphragm as indicated in Fig. 2 with the .rim [2 provided with alternate relatively strong and relatively weak portions indicated at and [6 respectively. The portions (5, which are separated by the portions l6, function accurately to support and center the diaphragm with respect to the supporting frame of the acoustic device and preferably are made of substantially the same thickness as the conical portion in so that they will have ample strength, and will have the ability to withstand the vibrations of the diaphragm for longperiods of time.

in order to increase the flexibility of the flange or rim the intermediate portions l5 are preferably formed as shown diagrammatically in Figs. 2 and I o of considerably reduced thickness. These weakened portions increase the flexibility of the rim in two ways, first, by removing some of the material of the rim and, second, by permitting thechanges in shape and distortion of the rim incident to vibration to take place more readily. That is, the relatively strong portions l5 may be distorted slightly in circumferential directions more readily than in a continuous rim structure. While the weakened portions (6 are of such thickness that they have very little structural strength and, in. fact, may be porous and even so thin as to be translucent, nevertheless the interlaced deposited flbers extend between the stronger portions i5 and form a suiiicient barrier to the passage Of sound and air to prevent the efficiency and acoustical qualities of the diaphragm from being impaired, whereas these qualities would be impaired if the material were completely removed from the regions i6. Further, the fibers make the flange substantially continuous and function to prevent the annoying phenomenon known as Hedge buz Thus, by providing weakened portions which nevertheless function as sound blocking portions, the stillness of the rim can be varied within wide limits to produce the desired characteristics without impairing the efllciency and acoustical qualities of the cone. Variations in the stiffness of the rim and correspondingly, in the natural frequency of vibration of the diaphragm may be produced by varying the spacing in size of the weakened portions 16, by varying their shape and general arrangement, by varying their strength and by other similar changes. For example, as indicated diagrammatically in Fig. 4, instead of reducing the thickness of the material in the weakened portions, the density of the material may be reduced as indicated diagrammatically at the regions 16a, the portions l5 of the rim 12a bein of normal density and strength.

In Figs. 5 to 9, inclusive, I have illustrated various arrangements of relatively strong and weak rim portions. In Fig. 5 the weakened portions Hib extend in spiral fashion from the conical portion of the cone toward the peripheral edge of the rim rather than radially as in Fig. 1. In Fig. 6 the portions I are circular rather than elongated as previously described. Fig. 7 shows weakened portions lid in the shape of sectors, while Fig. 8 shows a construction embodying a relatively large number of small weakened portions lia arranged in staggered relationship particularly along the corrugations H of the cone. Fig. 9 shows anarrangement in which alternately disposed large and small weakened portions if and [6a, respectively, are employed.

Various other arrangements will undoubtedly occur to persons skilled in the art.

The flexibility and adaptability of my scheme make diaphragms embodying my invention particularly desirable where the diaphragms are of non-circular shape. Thus in Fig. 10 I have illus trated a diaphragm of elliptical cross-section. In such a diaphragm I prefer to vary the stiffness of the rim in generally inverse ratio to the distance of the rim from the center of the diaphragm. Thus the least diameter of the elliptical diaphragm 20 is indicated at 2|, while the greatest diameter is indicated at 22. If the rim 23 were of uniform stillness throughout, the material of the cone 2! would be subjected to the greatest bending stresses along its major diameter 22 and to the least bending along the shortest diameter 2!. Such a diiierence in the bending forces exerted on the material of the diaphragm may result in impairing the acoustic characteristics thereof, and in order to compensate for this variation in diaphragms of this type. I preferably make the rim of the diaphragm more flexible adjacent the greater diameter and gradually reduce the flexibility of the rim as the smaller diameter is approached. For example, the rim may be provided with a plurality oi weakened portions 25, the weakened portions gradually increasing in size from the region adjacent the diameter 2! to the region adjacent the larger diameter 22. By this means the stresses in the material of cone can be stantially equalized with resulting improvement in the characteristics thereof. Obviously, 12nstead of varying the size of the weakened portions, their spacing can be changed or other means may be adopted to vary the stillness o! the diaphragm around the periphery of the cone Varying the stiffness of the rim is also of value in.

conjunction with diaphragms of other non-circular sections, such as the rectangular section described in my application Serial No. 351,791, aforesaid.

In Fig. 11 I have illustrated my present invention as it may be applied to a diaphragm with a diiierent type of flange. In this modification, the flange 21, extending from the body 28, may have a radially extending corrugated portion 29, an

axially extending portion 30, and a further radial portion 3 i The flange is provided with alternate strong and

weak portions

32 and 33, respectively, the portions 33 preferably extending along the axial portion 30 approximately to the Junction of the axial portion with the radial portion 3?. This provides a very flexible support for the body of the diaphragm. Obviously, the various modi fied arrangements of openings described heretofore may also be employed with flanges of this type. t

The diaphragrns embodying my invention may be made, for example, as described above, by depositing fibrous material upon a suitable form. The weakened portions may be produced by partielly or entirely mashing or blocking the open in. the porous form so that only a small amount oi fibrous material will be deposited ii the fibrous material is deposited by suction, and by generally similar masking of these areas it the fibrous material is sprayed upon the form. quantities of fibrous materials are d posited in. the weakened portions. In some instances this will result in. thinner portions, but if desired, the weakened portions may be made or substantially the same thickness; in this case lesser quantities oi. fibrous material are defiesited, but the diaphragms are subjected to a pressing operation to compact the deposited ma teriai compress it down to approximately the thickness deposited. in the weakened areas.

desired the diaphragms may be impregnated with the various materials heretofore noted. erably, the diaphragms are produced with enough. material in the weakened areas to support e. continuous film of the various impregnating me. terials, thus an impervious supporting flange can be produced, if desired, but, as noted above, a porous structure will also give excellent re suits.

From the foregoing description of my invention it will be seen that I have provided diaphragrn structures which can be economically and readily produced by my preferred methods, utilizing existing machinery and. without requiring extensive modification in existing processes. l'viy diaphragms, further, are adaptable to well known types of acoustic devices without requiring any modification thereof. By my invention the eiiiciency of acoustic diaphragms can be greatly increased as by reducing the stillness oi the rims the power required to vibrate the diephragms is reduced. Further, the stiffness of the rims can be controlled by varying the size and shape of the weakened areas so that die.- phragms having definite natural frequencies of vibration can readily be produced and such frequencies of vibration can be selected to suit the demands of the manufacturers of the acoustic devices. Further, by reducing the rigidity of the supporting rim, the response of the diaphragm may be made more nearly uniform over a wide range of frequencies and peaks in the response curves may be substantially reduced. All 0f these results may be obtained without any substantial impairment "in the acoustic qualities of Till the diaphragms and while the weakenedareas' have very little mechanical strength and offer little resistance to bending, nevertheless they are sufficient to block the transmission of sound from one side of the diaphragm to the other and do not substantially reduce the efliciency of the baille oi the acoustic device in which they are assembled. My construction further results in a considerable reduction in weight of the rim of the diaphragm and, accordingly, a reduction in the inertia thereof. For example, the weight of the rim may be reduced by half without seriously impairing the strength of the rim and while maintaining the rim as an accurate centering device for supporting the diaphragm.

' In the foregoing specification I have described various preferred forms of my invention. Those skilled in the art will appreciate that various changes and modifications may be made therein without departing from the spirit and scope of my invention. Accordingly, it is to be understood the foregoing description is given by way of example and not by way of limitation, and that my patent is not limited to the preferred iorn'is described herein or in any manner other by the scope of the appended claims when range of equivalents to which my may be entitled.

lteierence is hereby made to my divisional appli :tion Serial No. 439,142, filed April 15, 1942, which contains claims directed to thernethocl disclosed herein.

I claim:

1. An acoustic diaphragm comprising a body portion and a peripheral flange, said flange be ing formed of deposited fibrous material and comprising supporting portions extending from said body portion to the peripheral edge of said flange, and sound blocking portions integral with and oi lesser strength than said supporting per tions.

2. An acoustic diaphragm according to claim l, wherein the said. supporting portions are opauue and the said sound. blocking portions are so thin as to be translucent.

3. sin acoustic diaphragm according to claim l, wherein the flange is impregnated with one of the materials from the group consisting of lacquer, latex, synthetic resins, phenolic condense. tion products, and condensation products of urea and formaldehyde.

4. A one piece, seamless, acoustic diaphragm of deposited fibrous material comprising a body portion and a peripheral flange, said flange comprising supporting portions extendingirom said body portion to the peripheral edge of said flange and sound blocking portions integral with and or lesser strength than said supporting portions.

5.. A one piece, seamless, acoustic diaphragm of deposited fibrous material comprising a body portion and a continuous peripheral flange, said flange comprising supporting portions extending from said body portion to the peripheral edge of the flange and of substantially the same thickness and density as said body portion, and intermediate sound blocking portions integral with and of lesser strength than said supporting portions.

d. A one piece, seamless, acoustic diaphragm of deposited fibrous material comprising a body portion and a continuous peripheral flange, said flange comprising supporting portions extending from said body portion to the peripheral edge of the flange and of substantially the same thickness and density as said body portion, and intermediate sound blocking portions integral with and of lesser thickness than said supporting portions.

7. A one piece, seamless, acoustic diaphragm of deposited fibrous material comprising a body portion and a continuous peripheral flange, said flange comprising supporting portions extending from said body portion to the peripheral edge of the flange and of substantially the same thickness and density as said body portion, and intermediate sound blocking portions of substantially the same thickness as, and of lesser density than said supporting portions.

8. A one piece, seamless, acoustic diaphragm or" deposited fibrous material comprising a body portion and a substantially continuous peripheral flange portion, said flange circumferentially varying in strength.

8. An acoustic diaphragm comprising a body portion and a one piece substantially continuous peripheral flange, said flange circcumferentially varying in strength.

10. An acoustic diaphragm comprising a body portion of non-circular cross-section, and a peripheral flange adapted to support said body portion within an acoustic device, said flange circumferentially varying in strength and stiff-- ness.

ii. A one piece, seamless, acoustic diaphragm of deposited fibrous material comprising a body portion and a peripheral'flange, said flange comprising supporting portions extending r'rom said body portion to the peripheral edge of said flange and sound blocking portions integral with and of lesser strength than said supporting portions, said flange being impregnated with a material forming a continuous film co-extensive with said sound blocking portions.

12. A one piece, seamless, acoustic diaphragm i deposited fibrous material comprising a hollow body portion having a non-circular crosssectlon on a plane perpendicular to its and a peripheral flange adapted to support said body portion within acoustic device, said flange having diflerent strength characteristics in dif- Ierent regions thereof, and being strongest in the region closest to the axis of the body portion, and weakest in the region farthest from said axis.

13. An acoustic diaphragm comprising a body portion and a continuous peripheral flange, said flange circumferentially varying in strength and comprising supporting portions extending from said body portion toward the peripheral edge of said flange, and intermediate sound blocking portions integral with and of lesser strength than said supporting portions.

14. An acoustic diaphragm comprising a body portion and a one piece substantially continuous peripheral flange, said flange oircumferentially varying in strength and comprising supporting portions extending from said body portion toward the peripheral edge of said flange, and intermediate sound blocking portions integral with and of lesser thickness than said supporting portions.

15. An acoustic diaphragm comprising a body portion and a continuous peripheral flange, said flange circumferentially varying in strength and comprising supporting portions extending from asid body portion toward the peripheral edge of said flange, and intermediate sound blocking portions of substantially the same thickness as, and of lesser density than said supporting portions.

16. An acoustic diaphragm comprising a body portion and a peripheral flange, said flange having a circumierentiaily extending corrugation and being formed of deposited fibrous material and comprising supporting portions extending from said body portion to the peripheral edge of said flange, and sound blocking portions integral with and of lesser strength than said supporting portions.

17. An acoustic diaphragm comprising a body portion and a one piece substantially continuous peripheral flange having a circumierentially extending corrugation, said flange circumferentially varying in strength.

JOSEPH B. BEEN NAN.