US1927902A

US1927902A - Seamless diaphragm

Info

Publication number: US1927902A
Application number: US479593A
Authority: US
Inventors: Reed P Rose
Original assignee: Mechanical Rubber Co
Current assignee: Mechanical Rubber Co
Priority date: 1930-09-04
Filing date: 1930-09-04
Publication date: 1933-09-26
Anticipated expiration: 1950-09-26

Description

Sept. 26, 1933. R. P. ROSE SEAMLESS DIAPHRAGM Filed Sept. 4, 1930 2 Sheets-Sheet 1 Sept. 26, 1933. LR P ROSE 1,927,902

SEAMLESS DIAPHRAGM Filed Sept. 4, 1930 2 Sheets-Sheet 2 V(III'IIIIIIIIIVIIIIIIIIIIIIA w INVENTOR JZeed Zfiose ATTORNE Patented Sept. 26, 1933 PATENT OFFICE SEAMLESS DIAPHRAGM Reed P. Rose, Jackson Heights, N. Y., assignor to The Mechanical Rubber Company, Cleveland, Ohio, a corporation of New Jersey Application September 4, 1930. Serial No. 479,593

38 Claims.

This invention relates to new and improved methods for manufacturing diaphragms for radio loud speakers or other sound amplifying or reproducing units. According to this invention, the

complete diaphragm is made in practically one operation and is made entirely and integrally of a type of material which is particularly adapted for use in the amplification and direction of sound vibrations, and which can, by the use of the process herein shown, be made so that particular portions possess any desired degree of flexibility.

One object of the invention is to provide a method for forming acoustic diaphragms from fibrous material, preferably with' the admixture of other materials adapted to make the finished diaphragms moisture resistant throughout so that the performance of the diaphragm cannot be effected by variations in the, temperature and 2 humidity of the atmosphere.

Another object is to provide a means for varying the density of different parts of the diaphragm in order to better adapt it to reproduc different types of sound vibrations.

Another object is to provide a flexible suspension for a diaphragm of the type alluded to, so that the motion imparted thereto will not be retarded or interfered with by the supporting portions of the diaphragm. A further object is to provide a methodof increasing or decreasing the flexibility of any portion of the diaphragm by means of pressing and/or embossing the same in specially constructed molds under desired degrees of heat or pressure.

A further object of the invention is to produce a diaphragm for reproducing and transmitting electrically produced sound vibrations which is not resonant to any one of the audible frequencies, 40 which is flexible enough to receive and transmit vibrations without such resonances yet which still possesses the necessary stiffness and structural formation to enable it to perform the function of reproduction with fidelity and efiiciency.

Other objects and advantages of the invention will hereinafter appear when reference is had to the accompanying specification and drawings, in which ,Figure 1 is a perspective view of the frame- 50 work and parts associated therewith, of a device by means of which the novel method is accomplished;

Fig.2 is an enlarged perspective view of certain moving parts which operate in the frame illustrated in Fig. l-together with a diagram;

matic representation of operating means therefor;

Fig. 3 is an enlarged section of one of the suction molds used to accomplish the invention; and

Fig. 4 is a section of a finished diaphragm made in accordance with the invention;

Fig. 5 is a modified form of the periphery of a finished d aphragm;

Fig. 6 is a modified form of the apex of a fin-- ished diaphragm.

Diaphragms used in sound amplifying and reproducing units, such as dynamic radio loud speakers, consist generally of three sections which have heretofore been separately formed and cemented together, or otherwise assembled. The main portion of the diaphragm is the part which, on account of the vibrations imparted to it by the actuating coil, actually produces the sound by setting up sound waves in the air. The other two parts are those which secure this main section, respectively to the outer rim support of the device and to the voice coil. As the human ear is said to be sensitive to sound vibrations ranging from about 20 to 10,000 per second, the vibrating portions of the diaphragm must be supported by an extremely sensitive medium in order that these vibrations may be carried by the diaphragm without being damped or affected by the diaphragm suppo t. The two supporting parts of the ordinary diaphragm are usually made of soft leather or thin imitation leather or fabric and are fastened to the reproducing area. These materials have heretofore been considered satisfactory largely because there has been no other known material which could practicably be utilized for the purpose, yet the seams and joints necessary in this construction have in reality interfered greatly with the freedom of vibration of the diaphragm and have resulted in undersirable effects, such as resonance and rattling. Moreover, the abrupt variations in density and stiffness due to overlapped joints seriously impair the flexibility of the device at those points and result in extreme distortion of the sound waves set up. If the dia- 100 phragm material is not moisture-proof there will be additional evidence of poor' reproduction owing to changes in the moisture content of the diaphragm which will vary in accordance with the changes in humidity occurring in the surrounding atmosphere, causing the diaphragm to become too soft and dead, or too hard and brittle, or to be thrown out of adjustment in various ways. I In the present invention these undesirable qualities are minimized by the elimination of seams or other jointed surfaces, by the use of one type Per cent Cotton fiber 75 Rubber (from latex) Trinidad asphalt 8 Rosin 2 The above proportions may be varied to the following extreme:

Per cent Cotton fiber 25 Rubber (from latex) 50 Trinidad asphalt -i 20 Rosin 5 While I prefer to use rubber or rubber compounds for diaphragm construction, other nonfibrous constituents may be used. These may consist of any desired material which assists the rubber in makingthe finished product water resistant and providing the required properties in the completed article. The proportion may be varied at will to give the particular properties of sound reproduction and resistance to atmospheric changes required for the individual ideas of radio manufacturers.

The method of manufacturing sound reproducing diaphragms is as follows:

Any desired fibrous material, such as cotton fiber, wood pulp, etc., is placed in an ordinary paper making beating engine with water in the proportions of 3% to 10% fiber and 90% to 97% water' and beaten in the ordinary way until the fiber is in such condition that it will form a uniform sheet when run over a paper making machine. Upon completion of this treatment, or if desirable, during the treatment, a small amount of alkali, such as caustic alkali or ammonia is added, in a proportion to give a hydrogen ion concentration using the ordinary pH scale of from 8 to 12. After this has been accomplished the actual beating of the fiber is discontinued by raising the roll of the beaterof the bed plate, after which it simply acts as a mixer.

Rubber latex in the desired proportion, together with suspensions or emulsions of other materials made as hereinfater described, together with protective colloids, preferably of the proteinous type'may then be added. After these materials have been thoroughly and uniformly mixed with the fiber, a dilute solution of an acid salt or a mineral or organic acid is slowly added to the contents of the beater until a pH'of from 6 to '7 has been reached. At this stage the non-fibrous materials in the beater are agglomerated on the surface of the fiber, after which the addition of the solution of acid salt or acid is continued until actual coagulation has taken place and the nonflbrous materials are firmly bound to the fiber. This takes place at any desired pH under approximately four.

After this stage has been reached the fibrous material, together with its adhering non-fibrous material, is ready to form into acoustic diaphragms. This step can be accomplished through the medium of the apparatus illustrated in the drawings, which will now be described.

Reference character 1 designates a frame in which is mounted a tank 2 which may be provided with intake and discharge orifices through which the compounded fibrous stock is pumped and maintained at the required level. At each end of the frame are upright guides 3 adapted to guide slide blocks 4, to one of which is afilxed a vacuum valve block 5, connected by a flexible hose 7 to a suitable vacuum pump 42. In blocks 4 is journaled shaft 8 on which is mounted a number of suction molds in a manner similar to that illustrated in Fig. 2. The construction consists of vacuum header end blocks 6, one of which is arranged to interconnect at varying positions with valve block 5. To blocks 6 are connected vacuum header shafts 9 which in turn are connected to a gang of screen mold devices similar to that shown in Fig. 3. These may consist of finely woven wire screens 12 mounted on plates 11 and stems 10, the stems 10 being removably connected into the header shafts 9. Stems are provided with orifices 13 permitting the suction system to create a partial vacuum inside the screens 12 in order to form diaphragms in the manner about to be described. The screens 12 are illustrated as conical in shape but may be ellipsoidal, paraboloidal, or any desired shape.

Blocks 4 are mounted upon devices (Fig. 2) which accomplish an intermittent raising and lowering of the screen molds and which can perform this operation at times and during intervals to suit requirements. For convenience, the device at one end only is illustrated, it being understood that a similar arrangement is designed to raise and lower the other end of the apparatus synchronously with the end described. This consists of a piston rod 14 fixed to block 4 and extending downward into frame 15, in which are mounted cylinders 16 and 1'7. The piston rod 14 is provided at the lower end with a piston 18 which reciprocates in cylinder 16. Inside piston rod 14 is another piston rod 14' actuated by piston 19 which reciprocates in cylinder 17. At the base of each cylinder is connected air pressure supply mains 20 and 21 which are connected to

air valves

22, 23, 24, and 25.

Valves

22 and 23 are connected to a source of air pressure through main 35.

These valves may be actuated by a cam lever 26 which is rotatively mounted at 2'1 and held down on the cam 28 by spring means 29. Cam 28 is mounted on cam shaft 30 journaled in bear-v ings carried by supports 31. The shaft is actuated by a gear wheel 32 driven by a worm 33 which is connected to a source of power, illustrated here by motor 34. Clutch means may be provided between the gear and cam, if desired.

The stock is charged into tank 2, suction pump 42 started and power means 34 thrown into gear. Cam 28 raises the cam lever 26 which raises

valves

22 and 23 to open lines 20 and 21 to air pressure. Valves 24 and 25 are at this moment of operation, closed. The air pressure is admitted into the bottom of the cylinders and raises

pistons

18 and 19 so that blocks 4 and the screen mold apparatus are raised so that each screen mold is above the level of the liquid in the tank. As the cam slowly rotates, the cam lever is lowered, shutting off the air pressure admitted through

valves

22 and 23 and opening valves 24 and 25 which allow the air to escape and cause blocks 4 to descend until the pistons have reached the lower limit of their stroke, or until the air pressure is equalized one of a number of protective colloids.

against the weight of the screen mold apparatus or again raised to operate the pistons and raise the device. At this time the suction molds are immersed in the bath and the stock is being deposited on the screens 12 in a manner similar to that in which stock is deposited on the screens in a paper'making machine. The cam is further rotated in order to again admit air into the cylinders and to raise the molds from the bath. The cam may be so shaped that it will raise the molds partially from the bath and hold them there during the interval required to deposit a thicker layer of stock on the lower portions of the screens. Thus a very thin film of stock may be deposited on the outer rimof the screen and a relatively thick film on the inner portion or apex, resulting in a molded diaphragm of varying thicknesses. When the screens emerge from the bath, the shaft 8 is rotated 180 to position another row of screen molds for immersion, while the screens on the first row are removed. It can be seen that the arrangement illustrated may be regulated to effect an automatic timing which permits keeping any desired portion of the. mold in the fibrous suspension for any desired length of time, enabling a uniform ornon-uniform film to be deposited on the mold.

As hereinbefore stated, the material used in the practice of this invention may be any type of paper or sheet making pulp adulterated with non-fibrous materials, such as rubber, asphalts, waxes, natural and synthetic resin, inert inor ganic fillers, such as clay and coloring pigments, in the desired proportion, ranging from 25% fibrous material to fibrous material.

The fibers so treated carry the non-fibrous stock with them so that the liquid may be handled by pumps, pipes and in various sheet forming devices, such as paper making machines or suction molds.

The theory of the manner in which dispersions of the kind described are formed is briefly as follows:

In general, the non-fibrous materials are made toform a suspension by means of grinding or treating in a colloidal mill in the presence of any This treatment causes the formation of a film of protective colloid around each individual particle or globule of the non-fibrous material. It may be that the protective colloids surrounding the particles .or globules are in the form of a continuous film or sheath, or it may be that they simply exist in greater concentration on the surface of the particle than they do in the body of the suspending medium, at any rate they perform the function of keeping the rubber particles apart. Now it has been found that certain protective colloids, such as protein, soaps, etc., change their electrical charge from negative in an alkaline medium to positive in an acid medium, and that inert materials, such as cellulose fibrous asbestos and animal fibers, such as wool, finely shredded leather, etc., while having a weak electrical charge, have a negative charge in both alkaline and acid mediums. Consequently, when the non-fibrous ingredients are added to a suspension of fibrous material in water containing alkali, there is no attraction between the individual suspended particle and the fibers of material. But when, themedium is rendered acid by means of an acid salt, such as paper makers alum, or a dilute solution of mineral or organic acid, the charge on the suspended particle is changed from negative to positive and the particles migrate and attach themselves to the suspended fibers. It is precisely this condition that the stock must be brought to to accomplish the purposes of this invention.

The non-fibrous materials preferred in the production of acoustic diaphragms are rubber dispersions (obtained from natural latex, to which it is not necessary to add additional protective colloids, since proteinous protective colloids exist naturally in latex), asphalt suspensions or dispersions and suspensions or dispersions of ordinary rosin and waxes, such as parafin, carnauba, beeswax, etc., any of which may be combined with fiber to produce highly moisture-resisting and acoustic modifying products. It has been found that the presence of these non-fibrous waterproof materials in fibrous materials used for forming diaphragms, greatly improves the sound reproducing qualities of the material and also increases to a very great extent, the flexibility of the thin supporting portions of the diaphragm, particularly if the material is embossed or pressed under desired degrees of temperature pressure in order to form the material in varying densities, as hereinafter described.

The molds can either be raised immediately from the bath, thus giving a uniform thickness or deposit, or gradually raised to give a tapering deposit from the outer rim to the apex. Preferably, molds are used which are made of spun or pressed wire or perforated metal, and in order to secure desired variations at any portion of the diaphragm, the holes at this point may be made larger or smaller, as desired, thereby increasing or retarding the flow of water carrying the fibrous compound at this point. It may be desirable to arrange the molds to rotate as they are immersed but this is not necessary in the practice of this invention. The suction is maintained by means of a vacuum pump and any desired amount of vacuum can be maintained, the preferable amount being that found most satisfactory in practice in effecting a uniform deposit on the screen.

The molds may be made detachable from the supports so that they may be removed from the machine and the pulp deposit dried on them. This is "the preferable way of forming the diaphragms as shrinking or cockling is thus avoided. The drying is accomplished by blowing hot air around or through the mold or by placing same on rack guides that run into any ordinary type of drier. After the drying is completed the diaphragm may be removed from the mold by means of compressed air or by any desired method.

The diaphragm when removed from the mold sometimes is more or less rough in finish or appearance. Moreover, while the thickness of the fibrous compound will vary as above described, it will be found to possess practically the same density throughout. In order to finish the diaphragm and to secure variations in the density of the diaphragm at specified areas, the diarim as indicated at 39 in Fig. 4, or by engraving irregular surfaces throughout the entire metal surface of the mold, surfaces such as will simulate leather or wood graining or other material. A satisfactory break is effected by also arranging the dies to allow very small clearances in order to thin out the material at specified points in the corrugated areas.

When the unfinished diaphragm is placed in a mold, as described, and pressure applied, with or without heat, the density of the diaphragm is increased at the areas where the mold is designed to exert the most pressure. This can be varied within wide limits depending on the amount of compounded fiber in the various sections in the diaphragm. The suspending sections of the diaphragm may be made extremely flexible by virtue of a lower density of material in these sections and also by reason of the breaking action of the corrugated or engraved impressions described above. For example, the embossed or pressed diaphragm may vary in thickness from .005 inches on the outer rim and gradually taper to .020 inches in thickness at the apex. It is obvious that Where the' two portions of the mold make a perfect fit when the diaphragm is pressed, the greatest pressure will be exerted on the diaphragm at the thick section, and the least amount of pressure on the thin section, thereby giving a high density and stiffness in the thick portion due to the relatively high pressure, and an extreme flexibility in the thin section owing to the lighter pressure. In Fig. 4 is illustrated a diaphragm made in accordance with the invention, the portion 41 being thicker and more dense than the portion 40.

It should be noted that portion must not be made too flexible and that it is preferable to impart enough density at this locality so that the low frequencies set up by the voice coil will not cause buckling or whipping over this area of the diaphragm. In other words enough stiffness is built into the area adjacent the outer rim so that local movement at areas 40 is prevented and the diaphragm moves as a rigid whole at the lower frequencies.

The pressing operation described above is preferably made with heat and will cause the nonfibrous materials, such as rubber, asphalt, etc., since they are thermoplastic, to flow, and set into a fabric which not only possesses a highly finished polished outer surface, but also possesses the property of being substantially impervious to changes in the moisture content of the surrounding atmosphere when the diaphragm is put into use under varying atmospheric conditions. The outer rim or the apex of the diaphragm, may if desired, be dipped in compounded latex before embossing or pressing in order to increase the flexibility of the material at this point. The cure in this case occurs in the pressure mold. It is contemplated that these portions be dipped in natural latex and then sprayed, or painted with or dipped into compounds designed to facilitate proper curing in the mold.

The novel diaphragm constructed in accordance with the principles herein set forth not only reproduces low frequencies with fidelity but also effects a better reproduction of high frequencies than is effected by diaphragms heretofore known. The energy absorption of a diaphragm is generally considered as proportional to the mass of the diaphragm times the square of the frequency of vibration, thus where there is a considerable mass of diaphragm material to be actuated and actuation occurs at a relatively high frequency, the energy absorption is so great that the diaphragm as a whole does not move, and only the part of the diaphragm adjacent the apex is affected by the sound vibrations imparted. By virtue of the resilient material incorporated in my diaphragm, this action is greatly facilitated and the apex and adjacent area vibrate truly to the tune of the high frequencies imposed while the areas adjacent the rim, being resilient in a direction parallel to the surface of the diaphragm, allow the apex to receive and reproduce these vibrations without damping effect. Moreover, where the frequencies are in the middle zone, that is where they are of such magnitude as to effect a slight actuation of the rim, the ient action above alluded to assists the operation of the device by decreasing the inertia of the outer surfaces. The direction of motion allowed by the resilient material is illustrated by the arrows in Fig. 4.

A feature of the invention is that by making the diaphragm waterproof throughout, i. e. by making waterproofness a specific property of the material itself, local contractions in the diaphragm are avoided and thus is removed the cause for fluttering and distortion. The material retains its flexibility under varying conditions of temperature and humidity.

The specific means illustrated for accomplishing the novel method herein set out is not to be construed as the only means by which the method can be accomplished. Obviously other means can be used to carry out the novel ideas herein set forth. I do not wish to be limited to the particular means herein chosen as an illustrative way in which the invention may be practiced.

Having thus described my invention, what I.

claim and desire to protect by Letters Patent is:

1. The method of forming acoustic diaphragms which comprises forming a dispersion of nonfibrous waterproof, thermoplastic material and fiber stock, and then depositing the dispersed particles on a screen.

2. The method of making acoustic diaphragms which consists in forming a stock of fiber pulp and a dispersion of non-fibrous thermoplastic material, and then depositing same on a screen.

3. The method of making acoustic diaphragms which consists in forming a dispersion of nonfibrous thermoplastic material and fiber stock, depositing the dispersed particles in a film on a screen, and then drying and removing the film.

4. The method of making acoustic diaphragms which consists in forming a dispersion of nonfibrous thermoplastic materials and fiber stock, depositing the dispersed particles in a film on a screen, removing the screen, drying the deposited film, and then removing the film.

5. The method of making acoustic diaphragms which consists in forming a dispersion of non fibrousthermoplastic material and fiber stock, depositing the dispersed particles in a fllm on a screen, removing and pressing the film.

6. The method of making acoustic diaphragms which consists in charging paper making stock into a beater, beating said stock into .a uniform pulp, adding an aqueous dispersion of non-fibrous waterproof material, mixing the resulting mass, coagulating the non-fibrous materials onto the fibers, and then forming a film thereof.

7. The method of making acoustic diaphragms which consists in charging paper making stock into a beater, beating said stock into a uniform pulp, adding an aqueous dispersion of non-fibrous thermoplastic material, mixing the resulting ill mass, coagulating the non-fibrous materials onto the fibers, and then forming a film thereof.

8. The method of making acoustic diaphragms which consists of charging sheet making stock into a beater, beating said stock into a pulp of uniform consistency, adding an aqueous dispersion of non-fibrous waterproof material, mixing the resultant mixture, coagulating the non-fibrous materials on the fibers, forming a film thereof on a screen, and then drying and removing said film.

9. The method of making acoustic diaphragms which consists of charging sheet making stock into a beater, beating said stock into a pulp of uniform consistency, adding an aqueous dispersion of non-fibrous thermoplastic material, mixing the resultant mixture, coagulating the nonfibrous materials on the fibers, forming a film thereof on a screen, drying, removing, and then pressing said film.

10. The method of making acoustic diaphragms which consists of charging sheet making stock into a beater, beating said stock into a pulp of uniform consistency, adding an aqueous dispersion of non-fibrous thermoplastic material, mixing the resultant mixture, coagulating the nonfibrous materials on the fibers, forming a filmthereof on a screen, drying and removing said film, and then pressing same in a mold.

11. The method of making acoustic diaphrams which consists of adding a dispersion of non-fibrous waterproof material to a slightly alkaline stock of beaten fibrous pulp, mixing the stock with acidic material and then forming same into a film upon a screen.

12. The method of making acoustic diaphragms which consists of incorporating a dispersion of non-fibrous thermoplastic material in a slightly alkaline stock of beaten fibrous stock, mixing the resultant stock which acidic material and then forming same into a film upon a screen.

13. The method of making acoustic diaphragms which consists of adding a dispersion of non-fibrous thermoplastic material to a slightly alkaline stock of beaten fibrous pulp, mixing the stock with acidic material, forming same into a film upon a screen, drying and removing said film, and then pressing the same in a mold.

1 1. The method of making acoustic diaphragms which consists of incorporating a dispersion of non-fibrous thermoplastic material in a slightly alkaline stock of beaten fibrous stock, mixing the resultant stock with acidic material and then forming same into a film upon a screen, drying and removing said film and then pressingthe same in a mold.

15. The method of making acoustic diaphragms which consists of incorporatng a dispersion of rubber material in a slightly alkaline stock of beaten fibrous stock, mixing the resultant stock with acidic material and then forming same into a film upon a screen.

16. The method of making acoustic diaphragms which consists of incorporating latex in a slightly alkaline stock of beaten fibrous stock, mixing the resultant stock with acidic material and then forming same into a film upon a screen.

17. The method of making, acoustic diaphragms which consists of adding latex to a slightly alkaline stock of beaten fibrous pulp, mixing the stock with acidic material, forming same into a film upon a screen, drying and removing said film, and then pressing the same in a mold.

18. An acoustic diaphragm of fibrous material enmeshed in set thermoplastic material integrally united into a continuous mass of varying density.

19. An acoustic diaphragm of waterproof fibrous material integrally cured into a continuous mass.

20. An acoustic diaphragm of fibrous material enmeshed in set thermoplastic material integrally compacted into a continuous mass.

21. The method of making acoustic diaphragms which consists in forming a dispersion of nonfibrous thermoplastic material and fibre stock, coagulating the dispersed particles on the fibres, depositing the associated particles in a film upon a screen, removing the screen, drying the de= posited film, removing the film, and then mold= ing the same to vary the density thereof.

22. The method of making acoustic diaphragms which consists in forming a dispersion of non-= fibrous thermoplastic material and fibre stock, coagulating the dispersed particles on the fibres, depositing the associated particles in a film upon a screen, removing the screen, drying the deposited film, removing the film, and then alter-= ing its density in a mold.

23. The method of making acoustic diaphragms which consists in forming a dispersion of nonfibrous thermoplastic material and fibre stock, coagulating the dispersed particles on the fibres, depositing the associated particles in a film upon a screen, removing the screen, drying the deposited film, removing the film and then sub jecting the same to heat and pressure in a mold.

24. The method of making acoustic diaphragms which consists in forming a dispersion of non= fibrous thermoplastic material and fibre stock, coagulating the d'spersed particles on the fibres, depositing the associated particles in a film upon a screen, removing the screen, drying the deposited film, removing the film and then subjecting the same to pressure in a mold to vary the density of the film at predetermined areas.

25. The method of making acoustic diaphragms which consists in forming a dispersion of non fibrous thermoplastic material and fibre stock, coagulating the dispersed particles on the fibres, depositing the associated particles in a film upon a screen, removing the screen, drying the deposited film, removing the film and varying the density thereof at predetermined areas.

26. The method of making acoustic diaphragrns which consists in forming a dispersion of nonfibrous thermoplastic material and fibre stock, coagulating the dispersed particles on the fibres, depositing the associated particles in a film upon a screen, removing the screen, drying the deposited film, removing the film, varying the density thereof at predetermined areas and dis-= torting the fibrous construction at predetermined areas.

27. The method of making acoustic diaphragms which consists in forming a dispersion of non= fibrous thermoplastic material and fibre stock, coagulating the dispersed particles on the fibres, depositing the associated particles in 'a film upon a screen, removing the screen, drying the deposited film, forming a deposit upon the same from ill) an aqueous dispersion of rubber, and then molding the film.

23. The method of making acoustic diaphragms" persion of rubber upon predetermined areas of the same, and then molding the film.

29. The method of making acoustic diaphragms which consists in forming a dispersion of nonfibrous thermoplastic material and fibre stock, coagulating the dispersed particles on the fibres, depositing the associated particles in a film upon a screen, removing the screen, drying the deposited film, removing the film, contacting the same with an aqueous dispersion of rubber, and then varying the density of the film and the rubber deposited thereon.

30. The method of making acoustic diaphragms which consists in forming a dispersion of nonfibrous thermoplastic material and fibre stock, coagulating the dispersed particles on the fibres, depositing the associated particles in a film upon a screen, removing the screen, drying the deposited film, removing the film, forming an in situ deposit thereon from compounded latex, and then subjecting it to heat and pressure.

31. The method of making acoustic diaphragms which consists in forming a dispersion of nonfibrous thermoplastic material and fibre stock, coagulating the dispersed particles on the fibres, depositing the associated particles in a film upon a screen, removing the screen, drying the deposited film, removing the film, forming an in situ ,deposit thereon from compounded latex, and then subjecting it to heat and pressure while varying the density thereof.

32. A resilient waterproof diaphragm for dynamic radio speakers integrally formed of independent fibres associated with cured rubber particles.

33. A resilient waterproof diaphragm for dynamic radio speakers integrally formed of independent fibres associated with cured rubber particles, the density of the diaphragm being variable.

34. A resilient waterproof diaphragm for dynamic radio speakers integrally formed of independent fibres associated with rubber particles,

the density 01 the diaphragms being greater at the areas adjacent the center than at the areas adjacent the rim.

35. A conical waterproof diaphragm for dynamic radio speakers integrally formed of independent fibres associated with rubber particles, the density of the diaphragm being greater at the areas adjacent the apex than at the areas adjacent the rim.

36. A waterproof diaphragm for dynamic radio speakers formed in a substantially conical shape whose apex is distorted into the form of a cylin der having a closed end, said diaphragm being integrally formed of independent fibres with which are associated rubber particles, the density of the diaphragm being substantially greater at the areas adjacent its apex than at the areas adjacent its rim.

37. A resilient waterproof diaphragm for dynamic radio speakers formed in a substantially conical shape whose apex is distorted into the form of a cylinder having a closed end, said diaphragm being integrally formed of independent fibres with which are associated rubber particles deposited in situ thereon from an aqueous dispersion of rubber, the density of the diaphragm being substantially greater at the areas adjacent its apex than at the areas adjacent its rim.

38. A resilient waterproof diaphragm for dynamic radio speakers formed in a substantially conical shape whose apex is distorted into the form of a cylinder having a closed end, said dia phragm being integrally formed of independent fibres with which are associated rubber particles deposited in situ thereon from an aqueous dispersion of rubber, the density of the diaphragm being substantially greater at the areas adjacent its apex than at the areas adjacent its rim, and a vulcanized deposit derived from a compounded aqueous dispersion of rubber disposed over the outer rim.

REED P. ROSE.