US2585052A

US2585052A - Granule type acoustic transducer

Info

Publication number: US2585052A
Application number: US88770A
Authority: US
Inventors: Skelton Dennis Edward
Original assignee: International Standard Electric Corp
Current assignee: International Standard Electric Corp
Priority date: 1948-04-23
Filing date: 1949-04-21
Publication date: 1952-02-12
Anticipated expiration: 1969-02-12

Description

Feb. 12, 1952 D. E. SKELTON 2,585,052

GRANULE TYPE ACOUSTIC TRANSDUCER Filed April 21, 1949 2 SHEETSSHEET 1 s i 3 k 18 9 16 S IO? 6 BY W ATTORNEY Feb. 12, 1952 SKELTQN 2,585,052

GRANULE TYPE ACOUSTIC TRANSDUCER Filed April 21, 1949 2 SHEETS-SHEET 2 INVENTOR DENNIS E. SKELTON BY W ATTORNEY Patented Feb. 12, 1952 UNITED srAr-Es PATENT. QFFIZCE...

I V 2,585,052 I GRANULE TYPE. ACOUSTIC TRANSDUCER. Dennis'Edward' Skelton, London; England; as"- signor to International Standard Electric Corporation', New York, N. Y1, a corporation of Delaware ApplicationApriI 21, 1949, Serial N 0. 88,770 InGi'eatBritain April 23, 1948 (C1. Hik -123 l'Cl'aim.

This invention relates'to granule -type acoustic transducers.

The object'of the=inventiorr is to provide such transducers which are simple and cheap to manufacture;

One feature of the'invention isa granule-type acoustic transducer in which both the electrodes are thin diaphragms' suitably protected from damage;

According to another feature of the invention there is proVided a granule-type acoustic transducer=comprising aca'sing member on or in which are -mounted all' otherparts and which forms the peripheral wall of the granule chamber; seatings for front and'back electrodes, and a peripheral seating for. the diaphragm which is operatively associated with the front electrode.

The invention will be particularlydescribed with reference to two embodiments: shown in the accompanying drawings in which:

Fig. l is a cross section through a telephone type transmitter constructed'in accordance with the first embodiment of the" invention, and

Fig; 2' is a part cross sectional view of'those portions'of a transmitter according to thesecnd embodiment of the invention" which differ from corresponding portions shown in Fig. 1;

The transmittershownin' Fig. 1 of the 'accom panying' drawings comprisesa' die-cast zinc or aluminum casing member which comprises an annulardisc'portion' I, a" peripheral annular portion 2 joined to thejportionlby a cylindrical portion 3. The portion 2 carries a cylindrical extension 4- on the opposite side thereof from the cylindrical'portion 3T disc portion I carries an electrode chamber portion} with front and rear electrode faces 6, I and front and rear

cylindrical extensions

8, 9 defining electrode-fixing recesses I0, II.

The front and rear electrodes each comprise an annular peripheral portion and a central domed portion, respectively numbered I2, I3 and I4, I5. Both electrodes are made of carbonised nickel for example, in the manner described in British Patent No. 594,116, dated January 29, 1948. The front electrode is of the order of .003 inch on its inner edge the thick while the back electrode is of the order of electrodes capable-of manufacture by the same process from-similar'material.

The front electrode I2, I3 is fixed against its seating 6' by a cold'flowing lead ring I5 in therecess II]. The lead ring technique is described and claimed in copending U. S. patent -applica-- tion No. 627,945, filed November 10, 1945;- issued September 12, 1950, as Patent No. 2,521,744;

The lead ring I6 also positions an annular disc I! shaped internally and peripherally at I8, I9-to fit over the

portions

8 and 3; 2, respectively of casing member. Disc [1 is preferably of aluminium alloy and of the order of .003 inch'thick; Disc I'Ihas three equally spaced areas such as 20, of the order of 0.1 inch in diameter punched to form a fine metal mesh of nutmeg grater form" constituting an acoustic resistance which can be adjustedafter punching by compressing the prongs of the mesh as desired. The mesh resistance is considered preferable to the conventional silk-covered holes.

The diaphragm is of conventional design'but is axially apertured to form a substantially cylindrical ring of teeth 22 fitting into the interior of the domed portion I3- of the front electrode as described and'claimed in copending U. S. patent" application No. 704,965, filed October 22, 1946, issued January 30, 1951', as Patent No. 2,539,483. The central aperture in the diaphragm is closed by a disc 23'to prevent ingress of moisture be-'- tween the diaphragm teeth 22 and the front electrode surface.

The diaphragm 2| is peripherally heldbetween' the casing portion 4' and a' die-cast ormoulded apertured disc 24: 24 are fixed to the casing by a clamp ring 25 spun over the disc and casing portion 2, 4. The ring 25 may be of brass but preferably will be of the thermo-plastic material.

The rear electrode I4, I5 contrary to usual practice is thin and fragile and in consequence needs protection which is provided by a back cover plate 26 of for instance nickel silver of the order of 0.02 inch thick.

It is necessary to electrically insulate the back electrode I4, I5 and its cover 26 from the frame I-d. For this purpose the diameter of these two members is less than the diameter of the recess I I in which they are mounted and an annular insulating ring 21 for instance of mica is inserted between the face I of the frame and the back electrode. An annular ring 28 for instance of resin-bonded canvas is placed over the cover plate 26 and the back electrode assembly is secured by a lead ring 29 in the manner described Thediaphragm 21 and disc" 3 and claimed in copending U. S. patent application No. 627,945, filed November 10, 1945, issued September 12, 1950, as Patent No. 2,521,744. The lead ring may be pressed from sheet but probably the best way is to uselead wire cut to length and formed into a ring.

It will be noted that the back electrode l 4, l5 and its cover 26 are so shaped relatively that the cover will be guided by the electrode dome into correct relation with the back electrode. The back electrode l4, l5 and its cover 26 may be made into a subassembly prior to assembly into the transmitter.

The plane annular face of the front electrode l2, l3 on the convex side thereof and the carbon chamber peripheral surface 30 by the frame portion 5 are insulated preferably by brushing on white cellulose enamel and allowing to dry in order to concentrate the electrical conducting path across the carbon chamber to the zone between the domed portions I3, l5 of the electrode.

The zinc or aluminium die-cast casing 9 is in electrical circuit with the front electrode H! by contact of same with a portion of the casing, another portion of which is coated with a colloidal suspension of carbon or a silver paste and stored prior to assembly to assure a good contact surface for the contact spring when the device is assembled in thetransmitter housing of a bandset, for instance.

The casing portion 5 is provided with a filling hole 32 through which carbon granules or the like are introduced with the carbon chamber. The outer end of the filling hole is of greater diam eter than the rest to receive a closure disc 33 sealed in position with, for instance, a mass of clay shellac cement 34.

In assembling the transmitter, the back electrode assembly 21, l4, I5, 28 is first inserted into the frame recess l l and secured by lead ring 29. The clamping face of the front cover 24 is coated with sealing compound after which the diaphragm 2| and the front cover 24 are positioned and secured with clamping ring 25.

The granule chamber is now filled with carbon or the like on a shaking machine, after which the filling hole is closed.

In Fig. 2 the second embodiment of the invention is shown. In this there is provided a filling hole 34 in theback cover plate 35 and the space 36 behind. the apertured back electrode 31 is used as a granule reservoir. The aperture in the back electrode has a turned edge so as to prevent during operation the flow of current to it. Once again the back electrode assembly (in this case the

members

21, 31, 35, 28) may be first inserted into the frame recess H as a whole, the assembly being secured by the lead ring 29. In this embodiment of the invention a metal disc 38 is placed on the back cover plate after completion of the filling operation and its edges are crimped as shown at 39.

The diaphragm 2| in either embodiment may be formed of plastic material except for the toothed hub which would be of metal moulded or connected to the plastic diaphragm.

While I have described above the principles of my invention in connection with specific apparatus, and particular modifications thereof it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of my invention.

What I claim is:

A granule-type acoustic transducer having a metallic diaphragm constituting the movable front electrode and another metallic diaphragm constituting the relatively stationary back electrode, means for electrically insulating said electrodes from each other, means whereby said electrodes are arranged in spaced relationship, said back electrode having a centrally located aperture of such size as to permit free passage of granules therethrough, a cover plate, means for peripherally mounting said cover plate adjacent said back electrode to define a chamber communicating through said aperture in the back electrode with the zone between the electrodes, and granules substantially filling said zone and chamber.

DENNIS EDWARD SKELTON.

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

UNITED STATES PATENTS Number Name Date 1,186,746 Chisholm June 13, 1916 1,496,919 Bellus June 10, 1924 2,042,822 Bennett June 2, 1936 2,331,044 Pye Oct. 5, 1943 2,404,772 Brodie July 30, 1946 2,420,737 De Boer May 20, 1947 2,429,988 Bryant Nov. 4, 1947 2,435,920 Burroughs Feb. 10, 1948 2,451,317 Blair Oct. 12, 1948 FOREIGN PATENTS Number Country Date 599,633 Germany Dec. 4, 1934