US1730813A - Microphonic transmitter - Google Patents

Description

G. B. FRENCH MICROPHONIG TMNSMIT'LTR Filed April 12 1926 Patented Oct. 8, 1929 UNITED s'iAir-:s

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GEORGE B. FRENCH, OF SOUTHAMPTON, NEW YORK, ASSGNOR TO FRENCH ELECTRIC CO., INCORPORATED, 0F NEW YGRK, N. Y., A CORPORATON OF NEVI YORK MICRGPIEONIC TRANSMITTER Application filed April 12,

My invention relates more particularly to an improved method and apparatus'for accurately transmitting sound Waves or Waves adapted for the reproduction of sound Waves in an electro-magnetic receiving instrument. In other Words, my improvement relates to the employment Vof means capable of cooperation with a microphonic element in the transmission of sound Waves of pure tone and adapted to be reproduced more clearly and accurately than has been possible by the ordinary transmitting and receivine apparatus heretofore in use.

Heretofore itfhas been common practice,

,both in the transmitter and receiver, to use a diaphragm having a smooth surface, With relatively high reflecting qualities, and capable of considerable amplitude of mechanical vibration. Such a diaphragm is usually fas- ;tened at its periphery and, in the case of the transmitter, is adapted to be vibrated in response to the mechanical air pressures of ysound Waves impinging on the diaphragm.

In the case of the receiver, the diaphragm is adapted to respond to the varying pull of a magnet controlled by an electric circuit of variable strength.

In the ordinary microphonic transmitter, the diaphragm is adapted to vibrate with considerable, though Varying,l amplitude when sound Waves enter the mouthpiece of the transmitter, and these vibrations of the diaphragm are adaptedto vary the pressure upon the contacts between carbon particles Yor granules of the microphonic element, and thereby to vary resistance to a current passing therethrough. Flow of the current, therefore, will correspond more or less to the movements or vibrations of the diaphragm, which correspond in general to the sound Waves striking the latter.

These variable currents of the microphonic element upon passing through va -coil suirounding the magnet in the receiver, will cause' the diaphragm of the receiver to vibrate magnetically, according to the variations inthe strength of the current and thereby reproduce vibrations corresponding to the original sound vibrations impressed uponthe dia-` phragm of the transmitter.k

. duction.

1926. Serial No. 101,258.

It has been customary in priordevices to use diaphragrns, in both the transmitter and the ieceiver,",vhich have a considerable range of vibratory movement and also since *thel surfaces of the diaphragme used are usually hard and highly polished, the respective diaphragme are capable of considerable reflective action on sound Waves received thereby.

rlhis reflective character of the usual diaphragm, it has been found, Will result in considerable.l interference With the incoming the inicrophonic element are not iny accord With' the primary or original sound Waves it is desired to transmit. `As a result, these distortions and interferences prevent a pure tone.

reproduction of the sound Waves impinging upon the moving and reflecting transmitter diaphragm. Consequently, the vibrations produced by the diaphragm upon the carbon microphone are not exact reproductions of the original sound Waves.` There is still a further ldistortion due to the natural periodicity ofthe diaphragm. F or instance, in the type vof diaphragm novv in use there is a marked distortion of sound reproduced, due to the fact that the transmitting and receiving' diaphi'agnes,A which have their peripheries fixed,

have a variable amplitude of vibration from the center to the peripheryand these varying amplitudes affect the purity-of tone repronated, and receptionmaterially improved, by using a diaphragmor a' solid fdisc orblock sound Waves are preferably transmitted by molecular y Wave' motions v.vant-hin the material or the diaphragm.

These various objections anddefects of the ordinary transmitter may Abe-rey duced to a vminimum or substantially elimi-A Therefore, in overcoming these objections, my invention contemplates the use of a diaphragm, disc or block, forming the transmitting element, of relatively soft or soundabsorbing material, such as Wood, cork or the like, and of sufficient thiclrness to prevent any appreciable amplitudek of vibration thereof, as a Whole, in response to impinging sound Waves. Furthermore, my improvement contemplates minimizing or, to an extent sufficient for practical purposes, eliminating the reflection of sound Waves from the surface of the transmitting element, diaphragm or medium. Furthermore, the material used and the relative disposition thereof, as to the microphonic element, is arranged so as to give the diaphragm or transmitting velement a minimum amplitude of vibration and, therefore, a naturalV periadicity of low frequency. i

The primary object therefore, of my improvement is to provide a solid transmitting medium adapted to receive and absorb sound Waves and thence transmit them, by molecular vibrations Within the material, to a microphonic element, the latter being` so arranged that variation of the resistance is effected by the pressure of the transmitted molecular Waves, whereby the current in a receiving instrument is controlled to repro Y duce the sounds.

A further object is to provide a solid transmitting medium or element of this character with an absorbing or non-reflecting surface for receiving the sound Waves to be transmitted therethrough by molecular Waves to the microphonic element.

InV carrying out these objects in my improved transmitter, it is found that the objectionable characteristics, hereinbefore Vreferred to, are substantially eliminated and, since the sound Waves entering the transmitter are transmitted thro ugh a solid medium by molecular vibrations adapted to produce Waves exerting pressure upon the variable resistance of the microphonic element, the fundamental tones and over-tones or partials transmitted are clearer and purer and less subject to Vdistortion than those trans- `mitted by the ordinary diaphragm transmitter. As a result of transmitting sounds by my method, it Will be understood that the diaphragm of a receiving instrument in connection therewith, will emit sound Waves which are clearer and of much greater purity of tone, but of less volume, unless amplified as hereinafter pointed out. For this reason, it will be understood that, on account of the pure tones transmitted, the amount of ampliication Without distortion may be very much greater, and therefore, my'V improvement is particularly adaptable for the use of the deaf, for ordinary telephone lbroadcasting, for radio. broadcasting, for making talking-machine records and for other uses rea-r face thereof, formed by an annular flange Where correct and articulate reproduction of sound Waves is the desideratum, simply by the insertion of suitable amplifying means between the transmitter and the receiver.

ln the accompanying drawings, I have illustrated several forms and adaptations for carrying out my improvement, together with amplifying circuits, adapted to include a form of my improved transmitter. Fig. l shows one form of my improved transmitter, in which the diaphragm is made up of a thick disc of relatively soft material, such as Wood or cork; Fig. 2 is a side elevation of a modification, which may be substituted for the ordinary telephone transmitter; Fig. 3 is a horizontal section of the form shown in Fig. 2; Fig. l is a Wiring diagram, showing the arrangement as applied yto the ordinary poelret phone for the deaf, and Fig. 5 is a wiring diagram illustrating amplification of the transmitted sounds by the use of radio tube circuits.

Referring more particularly to the form shown in Fig. l, it Will be seen' that my improvement is applied to the ordinary type of microphone ti" ismitter, wherein the casing l is preferably provided With a cylindrical elongation f to provide for mounting therein a disc 3 of wood, corlr or other suitable material, of a character to absorb and then to transmit the sound waves by molecular vibrations of the material. lt Will be seen that the diaphragm or disc 3 is preferably made of sufficient thichness to practically eliminate vibrations of the diaphragm as a Whole. ln the present instance, the disc 3 is shown as `held in place by the front section 4 of the casing, Which is preferably spaced away from surface of the disc to form a compression chamber 5, substantially as shown in Fig. l. The usual mouthpiece 6 is screwed into a bushing 7, surrounding the perforations S in the front casing a, so that air sound Waves entering the mouth piece may be impressed upon the front face of the disc or diaphragm 3. The front face 9 of the disc 3 is preferably unpolished or even roughen'ed, so as to reduce the reflet-ting surface to a minimum. lf desired, the disc 3 may be relatively thin and have its front surface coated Wit-h a suitable sound absorbing material. Obviously, if the disc 3 is made of cork or soft Wood,

or roughened material, the natural surface of the material receiving the sound Waves Will beless likely t-o reflect them and hence absorption and molecular transmission thereby Will be more readily effected.

En the present instance, the disc 3 is preferably provided with a poclret or bore in the l0, in Which the n'ilcrophonic elementis in-V serted., This latter preferably comprises a small cup-like container ll in the bottom of which there is located one of the carbon discs 12. On top of the carbon dise l2, there is packed a quantity of carbon particles or granules 13, which are preferably packed solid and a. second carbon disc 14 is placed on top or" the carbon granules 13. The carbon disc le engages the bottom of the pocket formed by the annular flange 10 on the rear face of the disc 3, as Will be seen in Fig. l of the drawings. A lead Wire 15 may be connected With the inner carbon disc 111- and another lead wire 1G connected with the outer cui-bon disc 12 for completing the circuit to the receiver in the usual manner. The microphonic element ifi-L1- is arranged to lit closely between the rear face of the disc 3 and the wall of the rear casing 1, so that when sound waves as inolegular vibrations of .the solid material of the disc are transmitted therethrough to the carbon disc 14, the Waves thus transn'iitted will vary the pressure on the :arbon particles 13 and thereby vary the current flowing to the receiver, Which is adapted to reproduce the sounds, as previouslypointed out.

In the form of my iii'ipi'oveinent'shown in Fig. 2, instead of a disc or diaphragm, of Wood, corlr or similar material, adapted for the transmission of sound ivaves by molecular vibrations, I have substituted a block of Wood 17, which is provided with a pocket 18 in which the microphonic element is mounted. In this form, the carbon discs 19 and 2O are provided ivi-th s-"reiv threaded tcrn'iinals 21 and 22 to which the respective leads 23 and 24 may be secured for completing the circuit to the receiver in the usual manner. lVithin the pocket 1S and between the carbon discs 19 and 20, there is packed a quantity of carbon )articles 25 sufficient to comnletel and tightly lill the pocket and the space between the carbon discs, so that any vibrations Within the solid material of the Wood block will be transmitted to the carbon particles to vary the resistance in the mass thereof between the carbon discs, thereby varying the flow of current adapted for reproducing the Waves in the ieceiver. In this form of my improvement, the mout-li piece 26 is preferably formed of soft material, capable of absorbing sound Waves, such as cork or the like.

As previously pointed out, my improved microphonic transmit-ter is particularly adapted for use in phones for the deaf and a circuit for the usual pocket set is shown in the diagram of Fig. i1f. improved transmitter, substantially as shown in Fig. 1, is represented at 2?, as connected in circuit with a battery, 28., the circuit being completed through the primary 29, of an induction coil, the secondary SOof the induction f coil is connected b v lea-ds 31 with ear phones 32, which may be of the usual or any preferred construction. fith this form of circuit, the vibrations transmitted by my improved microphonic transmitter are amplified by the induction coil 29--30, and reproduced by the In this diagram, myV

receiver 32 inclear, puretones, for as pre-f viously pointed out, the sound Waves ieach-` Y ing my improved transmitter are transmitted through the discv 3 as molecularvib 1ations or Waves ofpure tones which maybe,amplified` enormously Without distortiomthe latter being 'an essential requirement' for a deaf phone. Furthermore, my improved transmitter eliminates'extraneous sounds, which in the ordinary deaf phone, produces a continuous hum ming ory crackling noise.

In F ig. 5, I have shown a Wiring diagram,

wherein amplification is effected by radio tubes and circuits, corresponding substan- Y tially to audio amplification inthe ordinary radio receiving set. In this diagram, my improved transmitteris represented yat 33, and is placed in the primary circuit 34 of an induction-coil, the secondary 35 of which is connected vwith the grid of a radio tube 36. The plateof theiradio tube36 is connected with the primary 37, of a second induction coil, thefsecondary 38'of which 'is connected fr with the grid of a second radio tube 39, the plate of which is connectedto the ear phones 4:0, substantially as indicated in Fig. 5. lVith radio tube amplification', as just described, it

has been found that the pure tones delivered or transmitted by my improved transmitter vdeparting from the spirit and scope of the invent-ion.

I claimt- 1.r A microphonic transmitterfcomprising a block of solid material uponwhich sound Waves may be impressed, the block of material being adapted to absorb sound vvaves and transmit them as molecular vibrations Within and through the'material, a mass of closely packed finely divided microphonicV material arranged to receive said molecular v vibrations and transform them into variable electric currents for operating a receiver, substantially as described.

2. A microplioiiic transmitter comprising a block of` solid material upon Which sound Waves may be impressed and transformed into molecular vibrations Within the materialand closely paclrediinely divided micro* phonic material adapted to receive said molecular vibrations and transform them into ioo isc

specified.

variable electric currents for operating -a receiver, substantally'as described.

3. A mierophonie transmitter comprising a solid block of material adapted for trans- Vmi ting sound Waves impressed thereon by molecular Vibrations Within the material, the sound receiving face of said transmitting block or material being arranged and adapted to absorb sound Waves, and a. mierophonie variable resistance conductor of solidly packed finely divided material mounted in cooperative relation with said solid transmitting block of material7 whereby said molecular vibrations set up therein are adapted to `vary the resistance in the mierophonie material and thereby Vary the eleetriecurrent passing therethrough, for theV purpose specified. f

' 4. A transmitter for sound Waves compris- ;ing a bloc-kof solid 'material adapted to transmit sound Waves impressed thereon by trans` forming them into molecular vibrations Within the material and transmitting them therethrough, and means associated With said lbloelr whereby said molecular vibrations Within the material thereof are adapted to Vary the resistance in a mass of solidly packed mierophonie material and thereby transmit Variable electric currents for the purpose GEORGE E. FRENCH.

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