US2396824A - Method of making diaphragm - Google Patents

Description

March 4 L. R. BURROUGHS 2,396,824

METHOD OF MAKING DIAPHRAGM Filed Sept. 20, 1943 /6. 5. P/ci 4.

IN V EN TOR.

BY mgf/ Patented Mar. 19, 3946 METHOD OF MAKING DIAPHRAGM Louis R. Burroughs, South Bend, Ind., assignor to Electra-Voice Manufacturing South Band, 1115.,

00., Inc.,

a corporation of Indiana Application September 20, 1943, Serial No. 503,094

1 Claim.

This invention relates to a method of making diaphragm, and more particularly to a method and means for mounting a diaphragm in a sound transmitting or translating device.

The diaphragm of a sound transmitting or translating device, such as a microphone, is commonly positioned or seated in the device by mounting means engaging the opposite faces of the margin thereof. The diaphragm must be held by such means in a manner which willnot interfere with full and free vibration of the diaphragm for true fidelity response thereof to sound waves, impulses or signals imposed thereon. Thus no stress should be imparted by the mounting means upon the diaphragm. Furthermore, the parts are so delicate or sensitive that even very small departures from a true fit of diaphragm and mounting may result in serious operating disturbances.

Therefore, it is the primary object of this in-- vention to provide a mounting which precisely fits the diaphragm.

A further object is to provide a diaphragm mounting which is formed from thermoplastic material which is fitted to the diaphragm by pressure While heated.

A further object is to provide two-part means for mounting a diaphragm by a. uniform perimetrical binding thereof under pressure ample to afi'ord a proper firm seating of the diaphragm and insufiicient to physically distort the diaphragm or prevent accurate vibratory response to sounds impinging thereon.

A further object is to provide a diaphragm mounting which serves as a seal against moisture.

A further object is to provide a novel and simple method for conditioning and shaping mounting means to the characteristic of the diaphragm mounted thereby.

Other objects will be apparent from the description, drawing and appended claim.

In the drawing:

Fig. 1 is a transverse sectional view of a microphone.

Fig. 2 is a face view of a mounting ring.

Fig. 3 i an enlarged detail sectional view illustrating the preassembled relation of the mounting rings.

Fig. 4 is an enlarged detail sectional view illustrating the assembled relation of the mounting rings to the diaphragm.

Referring to the drawing, wherein application of the invention to a microphone is illustrated, the numeral I0 designates a two-part hollow microphone housing. Each of the housing parts is substantially cup-shaped. The front part has a front wall II provided with sound passages I2 extending therethrough, and a thickened marginal wall I 3. The rear housing part has a rear wall I4. a thickened margina1 portion I5 and a central rear off-set I6 in which a pocket or recess, preferably of frusto-conical shape, is formed for communication with the cavity of the housing. A metal liner or button I! fits in said recess or pocket, and a conductor I8 is connected therewith and extend through the housing wall to provide a projecting electrical terminal I9. Screws 20 secure the contacting ma ginal housing parts I3 and I5 together.

A diaphragm 2I formed of a thin fiat disc or plate of metal has a central frusto conical integral off-set 22 projecting into button I I in coaxial spaced relation thereto. Diaphragm 2| lies in the parting plane of the housing sections, and a pair of similar rings 23 of resilient material are arranged in coaxial relation to off-set 22 at opposite sides of the diaphragm to span the spaces between the diaphragm and housing walls II and I4. Carbon granules or other suitable conductive granular material 24 fills the space within the rear ring and engages the diaphragm and the button.

Each of the cup-shaped housing parts mounts a diaphragm seating ring 25 fitting snugly therein against the thickened marginal housing portions I3 and I5. These rings are formed of thermoplastic material of the synthetic resin type of which vinyl resin copolymer, cellulose acetate and acrylics are examples. The inner side face 26 of each ring is preferably radially or transversely crowned or contoured as illustrated in Fig. 3, and the initial overall thicknes thereof is preferably approximately about .010 of an inch greater than the thickness required to contact diaphragm 2| at its margin when the device is assembled. Therefore, since the thickness of a diaphragm is in the order of .005 of an inch, it will be seen that the crowns of the rings project beyond the planes or faces of the marginal housing portion I3 and I5 which are intended to engage when the microphone is assembled. The diaphragm is preferably secured to one housing part, as by means of an integral tongue 21 projecting therefrom and imbedded in marginal housing portion I5. The outer end of tongue 21' preferably projects from the housing to form a terminal 28.

To properly condition the parts for assembly of the microphone, and particularly to reshape or reform the excessively thick or oversize rings 25, the parts are positioned with the rings 25 and diaphragm 2I in proper registering 0r coaxial relation while rings 25 are in a heated condition.

2 Pressure is then exerted axiany with the parting faces of marginal housing portions l3l5 are brought into full face engagement. The application of pressure in this manner reshapes or reforms the rings 25 to precisely fit the diaphragm 2|, and entails a flattening of the crowned ring faces as shown in Fig. 4. The application of pressure is continued until the rings have taken a permanent set in this shape. One material of which the rings 25 may be formed i known commercially as Vinylite," and when this material is used, satisfactory results are obtained when the same is heated above the softening point, as from 150 to 220 or more, Fahrenheit, incident t the pressing operation.

An alternative process is to insert the rings 25 in the housing parts, position the preassembled units in registration with the diaphragm therebetween, apply pressure to the registeringparts, and heat the registering parts while maintaining the applied pressure. This necessitates formation of the housing from materials such as metal, or plastics having a substantially higher softening temperature than the material of which rings 25 are formed. In some instances it may be necessary to follow a procedure wherein each ring is individually reshaped. For instance, a metal ring or plate may engage one surface of the diaphragm as pressure is applied to an assembly including said metal plate, the diaphragm, one ring 25 engaging the opposite diaphragm face, and the housing part mounting ring 25. The operation is then repeated to form the face of the ring 25 which is to engage the face of the diaphragm against which the metal plate bore during the first operation. Such a two-step process may be necessitated when the conditions are such that simultaneous forming of both rings might introduce distorting stresses in the diaphragm, as when the diaphragm is exceedingly thin and the opposed rings are not preformed to exact equal thickness. The processing of the diaphragm-engaging parts, including the housing also in the one embodiment, provides amounting for the diaphragm which is exactly and precisely fitted to the particular diaphragm to be mounted thereby and to the housing parts which mount the rings. Thus the rings are reset or reshaped to the exact form required in each instrument ordevice. Assembly of the device. completed by the securing together of the housing parts with their marginal ortions in face engagement, eflects a full, firm and uniform positioning engagement of each ring with the diaphragm margin. This prevents physical distortion of or application of stress to the diaphragm, so that the diaphragm may have a full free vibratory response to sounds, impulses or signals impinging thereon. At the same time. the face engagement of rings 25 with the diaphragm is of such character that no moisture can penetrate therebetween, and the microphone or other device is effectively sealed or rendered waterproof at the parting plane or its housing.

While the diaphragm mounting rings 25 have been illustrated as solid, they may be formed of tubular cross section, if desired. Where tubing is employed, the application of pressure while the ring is heated entails alteration of the cross sectional shape thereof and conformance of surface contours thereof with the diaphragm faces with less pressure than required with solid rings. Also, the possible adverse effects of extrusion of the ring material, such as production of a greater area of contact of the rings with the diaphragm than desirable, are avoided.

While the invention has been illustrated as applied to a microphone, it is obviously applicable to devices of other types, such as car phones and to devices sensitive to or for the measurement of pressures.

I claim:

The method of mounting a diaphragm between similar opposed rings in a housing formed of a pair of recessed parts, consisting of the steps of inserting oversize thermoplastic rings in said housing parts and pressing said housing parts against opposite faces of a coaxially interposed diaphragm while said rings are heated to a softened state.

LOUIS R. BURROUGHS.

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