US2100975A - Sound recording - Google Patents

Description

Nov. 30, 1937. NEUMANN 2,100,975

SOUND RECORDING Filed Aug. 17, 1936 FIG. I.

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. /NVENTOR Patented Nov. 30, 1937 UNITED STATES PATENT OFFICE SOUND RECORDING Application August 17, 1936, Serial No. 96,513 In Austria December 13, 1935 1 Claim.

This invention relates to means for recording acoustic oscillations. For the recording of sound, more particularly with dictating machines and similar apparatus, there have hitherto been em- 5 ployed essentially two methods, namely the mechanical method and the electrical method. The mechanical recording method, although simple, is attended by the drawback that the orifice of the speaking tube must be held close up to the mouth, which is in itself a great inconvenience in dictating machines. Furthermore, recording is restricted to the locality of the machine. The amplitudes of the recorded oscillations are slight According to the second known method, there is employed for sound recording a microphone which either operates an electric recording (cutting needle) sound-box or acts, by means of an electrically excited diaphragm through the intermediary of an interposed column of air, upon an 9 acoustic recording sound-box the diaphragm of which is of approximately the same order of magnitude as the electrically excited diaphragm.

In order to obtain amplitudes of sufficient magnitude for clearly audible reproduction multistage amplification of the speaking current impulses supplied by the microphone is necessary during recording, even when the energy supplied by the microphone would be in itself sufficient to meet the energy consumption required to form sound grooves of large amplitude. The reason for this is to be found in the fact that the maximum amplitude of the electrically operated diaphragm is dependent on the voltage of the alternating current applied, since the counter-electromotive force generated by the diaphragm in the exciting coil can not exceed the voltage of the alternating current applied. An increasing of the amplitudes by leverage is not admissible, since in consequence of the high transmission ratio an excessively long lever arm would have to be used which would either be not strong enough and set up independent oscillations or be of too great a mass which would give rise to distortions through inertia. Double or multi-efiect leverage systems are not feasible, since it is impossible to eliminate play in the bearings, and the resulting losses and inaccuracies are excessive.

In accordance with the present invention, which provides means for the recording of acoustic oscillations comprising an electrically excited diaphragm which closes over one end of a soundconducting tube into the other end of which there is inserted an acoustically operated recording (cutting needle) sound-box, the oscillations of the electrically excited diaphragm are magnithe case 5 of the talking machine.

fled with the least possible distortion and with a minimum of loss. In accordance with the invention this result is'achieved by the arrangement that the electrically excited diaphragm. is larger than the diaphragm of the acoustically operated recording sound-box, with theresult that" the amplitudes of the larger diaphragm are converted into larger amplitudes of the smaller diaphragm. There is thus effected transformation of the availableenergy of oscillation. The os- 10 cillations of the large diaphragm are of slight amplitude but relatively great strength, and through the transmission according to the invention these oscillations impart to the diaphragm of the acoustically operated recording sound-box,.15 practically without distortion and without loss of energy, oscillations which, While'being of less strength,are of greater amplitude.

A form of construction embodying the invention is shown, by way'of example, in the accompanying drawing which shows the invention diagramm.atically,in longitudinal section, in Fig. 1, as applied to a phonographic or talking machine using disc records, and in Fig. 2 for use with cylindrical sound records.

A sound receiving member is employed, a microphone I which is supplied with current from the battery 2 consisting for example of two dry cells. The speaking current impulses from the microphone are transmitted through the microphone transformer 3 to the conductor 4 and fed to the loud speaker installation 6 disposed in For the operation of the, loud speaker there can be employed any readily responsive system. It is advanta- 35 geous, however, to adopt the simple electromagnetic systems, since they fulfil this requirement, and energies of a greater order of magnitude are not available, since the set works without amplifier or with but slight amplification. These 40 electromagnetic systems, however, work with slight amplitudes, so that magnification is necessary to enable operation of the cutting needle or stylus to be effected therewith, and. this magnification of the oscillations is required to be 45 effected as nearly as possible without incurring any losses. Furthermore, the electromagnetic system must work at full load, since it is only then that it can give maximum output. This full loading is obtained by connection to a suitably'large 50 area diaphragm 1. which directly adjoins the wider end ofthe horn 8 of the phonographic or talking machine. The narrow end of the tone arm is closed over by the far smaller diaphragm 9 pertaining to the acoustically operated recording 55 sound-box by which the cutting needle or stylus I0 is operated. The vibrations of the diaphragm 1 are converted, in consequence of the large area of the oscillating surface, into powerful compressions of the body of air entrapped in the horn, which compressions in their turn bring about vigorous vibration of the smaller and more readily oscillating diaphragm 8, so that the sound groove traced is of adequately pronounced amplitudes, in consequence of the thus effected magnification of the original oscillations.

The form of construction shown in the drawing is intended for the recording of sound on discshaped phonogram carriers. The turn-plate H is driven by a clockwork motor l2. To the arm l3 of the horn or tone-arm, which is pivoted in a known manner, there is attached a half nut l4 which engages a screw spindle l5. This spindle I5 is driven by means of countershaft worm wheel gearing l6 and bevel wheel gears ll, I8, from the clockwork motor l2, and during the recording guides the sound-box transversely across the record disc l9, so that the stylus cuts the sound groove in the form of a spiral.

When the recording method according to the invention is applied for instance to a dictating machine to be used in an oflice it is advantageous to provide merely the microphone in the vicinity of the person dictating, while the recording apparatus is kept in another part of the ofiice. In this case the tone arm 8 is provided with a closable flap or door 2|, so that the person in attendance on the apparatus, after opening this flap, can hear everything taken up by the microphone. A telephonic connection is thus provided between the person dictating and the person. tending the recording machine, by means of which the person dictating can instruct the person at the apparatus for example when to close down the fiapand to start up the apparatus for recording.

I claim:

In apparatus for recording acoustic oscillations a. sound-conducting tube filled with a gaseous fluid, an electrically excited diaphragm at one end of the said tube and adapted to close over the said end, and an acoustically operated recording sound-box built into the other-end of the said tube, the said electrically excited diaphragm being of larger area than the diaphragm of the said acoustically operated recording sound-box, so that the oscillations of the said larger diaphragm are converted into oscillations of the smaller diaphragm of greater amplitude, as and for the purpose specified.

- LEOPOLD NEU'MANN.

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