US1558643A - Telephone transmitter - Google Patents

Description

Cct. 27, 1925- 1,558,643

A. B. SMITH TELEPHONE TRANSMITTER Filed May v, 1923 M Y f j' Im flhm? BEESEL-f Eh Planea oet/27',

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Y 'm' Ep` TM *N' 'smetta Tov'izllw'hom z'tlmayconoem: p n n Be itvknown'that I; ARTHUR Basenr SMrrn, 'f-a 'citizen of the Unitedv States of America, and-are'sidentof Evanston, Cook -Colin't'y, '5 and State of Illinois, have invented `'certain new Land nseful 4Improvernents in Telephone u Transmitters, of, which the-following' is ka specication.4 l i n y y p A My invention relates in general to' telephone transmitters, more in particular tqhtrahsmit'ters iin which the microphone velt'e'iient is of the ",igranillar 'Carhol'rL type, fand the object o f-tho invention isto rovido a microphoneyvhich is well adapted Voropera- ,'15 tion Zonrelatively vlow current values and v,whioh has Vtoojnn;parttively high resistance.

Broadlystated, the desired objectjis'aep coinp'lished by interposingathin diaphragm ofv-mica orother insulating vmaterial `between. the two electrodes lof the mieiophelie;-A

-The diaphra has a numberzofuopenings through whyio free communication vis man1- tained` biwen the chambers on Aopposite 'sides thereofeo far asco'ntaetland passage of the granu'lates is' concerned, b't vsflrih aredmallenogh, nevertheless, to senslbly l restrict the leective cross-section of the gralilar ma'ssf In'l additio lthe opemn'gs t are so disposed as to.a1`pxl7ee1a`blyy lengthen the crrent path between the electrodes. Thus thelincreased re's'stll is secared` in 3l Y `e precisie Imarmeigi'n `which the inten. I tion is carried outwill b descnbedvfully hereinafter, reference being h ad tO-the ac# oompanying" drawing', in which l Flgz 1 1s la cross section throughtl ,well tpe of transmitter .Lnxbodyirlg the inventlon,

while Fig. 2hows the diaphragrin,v hereinifi before Areferred to as bang interposed botv'vgaan the electrodes. ,n Eicept for the microphone element, the

5 transmitter myibe '0f any Walkowil fleaigu. l- Aa'illiisnfaai inj the `drawing itoom.A

' almoiltll piece 1; faceplate 2 having anf onelrngfn which tl'l'oY mouth pieee. is

e ,held by screwthreadsj, ,aheyy yflanged rlng 5 3, screed .-"into the :rearwardly extending rimfof the face "plateas shown; a bridge 4,- "which is formed integrally with thefrin'g 8;'.and aiicrophoe cell supported in the to maman lapin preferablyvof hard rubber, bakelite, .or other sultable insulating material, and on the in- `sido. is oynndrcar in` sha Le for the greater part. of its depth, there eig, however, va'

conical depressionvat thebottom of the cp whlchterminates in a countersnk opening; The stern/9 asses through; this `o ening and a` correspon ing bli'shed hole in brldge 4, and a nut .10, is' employed to clamp. the oup 'to the, bridge. The rear electrode 11 is ofoar;

bonelectropglated dii one l'side and is soldered to the rear end of the stem 9. Its exposed surface isy polished and is iush with the bot`- toin ofl the conical depressionjin the op. The. partition 2o, shown most clearly in' Fig.v 2 is preferably -'of mica, Aperforated,,as shown, andgrests at. the bottom Iof theoylim dricalvpotoof the ciip. To the left ofthe partition 20` isfabrass ring 19 whose outer edgel isfiush with the edge of thecx' The.

front electrode 17 is attached vto the ead of 12 in the samelnaner as electrode 11 is attached -.toi stem, 9, V,and isslightly larger.

diaxneterthanthelatt'er electrode.` I )larhrapfm 21, of micaalso and ilsfed forseallngtheend ofthe cup, 1s perforated .in ,the

center to periitfit to be 'slipped in place over fst'ejnfry 12 where it is.A secure 5 and, nut l15; e The diaphfagmel is clamped against the brass rin" 19 by means of the threaded. cap 18,vcfl1'1'ch also Serves, there-v fore,- lto securely hold the l:said lring and the partition 20 .in glace.` -Stem 12 isl agmtby means ofpnut's The' grgnalaarbonis of oouree intro- Yduced before the op is sealed by lampn'" diaphragm 21 in place, and should by washer 1o f cient qantity. to nearly, ll 4the Carbon ofthe standard nelne'ss'inay -4 as in ordinary piicrophones, lthe opemngag the partition 20 being much larger than the individual grains in the standard grade of carbon, so that free circulation 1s maintained at all times.

In operation, the current cannot pass directly from one electrode to the other, owing to the partition, but must flow outwardly from one electrode toward the outside of the mass of carbon in order to pass through the several openings and reach the other electrode. It will be understood therefore that the conducting path through the granulated carbon is somewhat longer than it is in the ordinary microphone without the partition, in which the current can pass directly from one electrode to the other. `It will be noticed also that the partition reduces to a considerable extent the effective cross section of the conduct-ing mass of carbon; that is, in-

stead of being approximately equal to the actual cross section,the effective cross section is approximately equal to the sum of the areas of the several openings in the partition, which is a smaller value.

It will be evident from the foregoing that the relative size of the parts, and in particular the size and position of the openings in the partition, is of great importance in securing the desired results, and that by suitably varying one or more of the essential dimensions any resistance desired may be obtained within a considerable range. The following table gives the principal dimensions in a working transmitter embodying the invention which vgave excellent results:

y Millimeter'. Diameter of 'rear electrode j i 6 Diameter of front electrode l 8 Distance between electrodes 2. 1 Numberof openings in partition; 'i 6 Diameter of vopenings in partition 2. 5 Diameter of circle enclosing openings- 11. 2

The transmitter referred to above had a resistance ofapproximately 400 ohms workin on a current of .O amperes.

consider to be new and' desire vto have'fprothespace between said electrodes, an auxiliary diaphragm parallel to and midway between said electrodes, said diaphragm having a centrally located insulated portion equal in size to one of said electrodes, land a plurality of openings outside of said insu"- lated portion, said auxiliary diaphragmgreducing the effective lcross section areafof the comminuted resistance material and also increasing the length of the currentpath through it.' I

In witness whereoffI 'hereunto subscribe my name this 4th day of May, A. D., 1923.

ARTHUR BESSEY SMITH.

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