US2318417A - Artificial reverberation system - Google Patents

Description

y 1943. w. D. PHELPS 2,318,417

' ARTIFICIAL REVERBERATION SYSTEM Filed June 2, 1942 Fig [Sc/1L5 MOIJEL OFA/V AUDITOR/0M /7 WALL OPEN/N6 f ED: MODULATOR LAYER 0F S l/1V0 ABSORBE/VT MATERIAL NOV/181.5 WALL Pi 2.

J6 A. E mm :1; I MODULATOR H fl 3 52 L NODl/LATOR ln /efitor l William D. Phelps, b Mm f b His Atfl ohneu Patented May 4, 1943 William D. Phelps,

Schenectady, N. Y., sssignor to General Electric Company, a corporation of New York Application June 2, 1942, Serial No. 445,471

Claims.

My invention relates to systems for producing artificial sound reverberation, particularly to systems for adding artificially created reverberation of suitable characteristics and amount to voice, music, or like audio-frequency soimd signals having initially included therein no reverberation components or negligible amount thereof.

The general object of the invention is to provide improved devices for thus producing and adding artificial reverberationwhich are simple and eflicient and which, in particular, are of dimensions preferably small relative to corresponding means and devices hitherto employed or suggested forv insuring desired reverberation effects in the above-mentioned or other like audio-frequency sound signals.

In accordance with my present invention, this general object is attained by first providing, for the purpose of adding the desired reverberation components to an audio-frequency sound signal having no reverberation components or a negligible amount, a reverberation device which is preferably of reduced dimensions relative to a corresponding reverberation device, of fullsize or normal dimensions, which would add desired reverberation components if the abovenoted sound signal alone were generated there in, next generating within the reverberation device of reduced dimensions a superaudible carrier sound frequency which is modulated by the above-mentioned unreverberatedsound signal frequency, and finaiLv detecting from the modulated super-audible sound frequency the original audio-frequency sound signal to which has been added within the device of reduced dimensions the desired reverberation components.

By thus employing the high frequency or super-audible sound wave as a carrier for the audio-frequency sound wave, reverberation eflects will be produced in the reverberation device of reduced dimensions as in the similar device of normal dimensions wherein the audio-frequency sound wave is employed alone, without the carrier wave. The high) frequency carrier wave which permits the above-mentioned small reverberation devices to be employed to produce this result, and that, by suitable proportioning and arranging of the small reverberation devices, desired reverberation components, having a time of decay of the order of the time of decay of reverberation produced in a corresponding reverberation device of normal size, are added to audio-frequency sound signal having initially no reverberation components or a negligible amount of these components.

The reverberation device, in accordance with my invention, may comprise an enclosure, the shape and general arrangement of which are that of a full-sized or normal auditorium, having a desirable reverberation characteristic preferably scaled down so that its dimensions are of the order of at least a wave length of the carrier frequency.

In addition to air as a medium in a reverberation device wherein reverberant sound energy is produced and transmitted in a small enclosure, in accordance with my present invention, solids and liquids may also be employed in the reverberation devices of small dimensions.

The novel features which are considered to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing wherein Fig. 1 is a diagrammatic representation of a voice signal system for adding reverberation in a small enclosure to a voice signal having initially no reverberation component; Fig. 2 is a modification similar to the system of Fig. 1 but which provides means for obtaining a reverberant or a non-reverberant signal, or of combining the two in any desired proportion; Fig; 3 is a modification employing a metallic mass as a reverberation device; Figs. 4 and 5 are further modifications similar to that of Fig. 3; Fig. 6 is a modification employing a liquid element as the reverberation device; and Fig. 7 is a modification employing a plurality of differently resonant metallic elements in the reverberation device.

In the system illustrated in Fig. 1, the numeral l0 designates an audio-frequency sound signal device such as a microphone or the like, numeral I I designates a small reverberation device or enclosure having the form of a reduced scale model of a given auditorium assumed to be desirably arranged as to reverberation characteristics for the reproduction and audition therein of an audio-frequency sound signal such as is impressed upon and translated by the microphone l0, and numeral i2 designates a sound signal output device such as a loud-speaker. The enclosure II is preferably provided with means for adjusting the reverberation characteristics thereof comprising, for example, a movable wall It for varying the volume of enclosed air, windows or free openings l4, adjustable shutters ii for varying the area of the openings, and sound absorbent material iii, if desired, over certain areas of the inner wall surfaces.

To utilize the relatively small auditorium model II as a source of artificial reverberation to be added to the original audio-frequency sound signal, a source ll of electric oscillations of ultrasonic or superaudible frequency, for example of thirty-thousand cycles per second, is provided, connected to a modulator i8 to which the microphone I is also connected. The modulator is connected through a suitable intermediate frequency amplifier stage or stages 19 to a loudspeaker or like telephonic transmitter device 28 mounted at a desired point within the reverberation device or enclosure ll. At another point within the enclosure is mounted a micro phone or like pick-up device 25 which is connected to a detector stage 22. The output of the detector stage is connected through a suitable audio-frequency amplifier stage or stages 23 to the sound output device or loud-speaker i2.

In operation of the above-described system shown for illustrative purposes in Fig. 1, the superaudible electric carrier wave produced by the source of electric oscillations I! is modulated by the audio-frequency electric signal oscillations from microphone Ill. The modulated electric signal is amplified in the amplifier stages l9 and impressed upon the loud-speaker or like device 20 for converting, within the enclosure ii, the modulated electric signal into a corresponding sound signal constituted by an ultrasonic or superaudible carrier sound wave modulated by the original audio-frequency sound signal.

The modulated superaudible sound signal containing the desired reverberation components produced in the enclosure ii is picked up by the microphone 2| and translated thereby into a corresponding electric signal from which is recovered, in detector 22, the audio-frequency electric signal which now contains the desired reverberation components. The latter signal is impressed upon the loud-speaker or like translating device i2 which reproduces the original audiofrequency sound signal with the addition thereto of the reverberation which was produced, within the enclosure ii, in the modulated superaudible carrier sound wave.

The sound producing and reproducing devices 20 and 2| may be of any suitable type well known in the art but preferably are of piezo electric or magnetostrictive type.

Referring to Fig. 2, the arrangement and operation of the system illustratedtherein are the same as for the system of Fig. 1 except that in I the system of Fig. 2 the input audio-frequency sound signal containing initially no reverberation, and this non-reverberant signal which has reverberation added thereto by the means described in connection with Fig. 1, are combined in any desired proportion. For this purpose, in Fig. 2 the original signal is bypassed around the arti ficial reverberation means and is impressed together with the signal detected from microphone 2i upon the sound producing device or loudspeaker I! as by connection of the output of microphone ill to the audio-amplifier 23 through suitable connections 24.

Referring to Fig. 3, the system therein illustrated may be similar in general to those of Figs. 1 and 2 except in the construction and manner of operation of the reverberation device employed. Instead of employing the enclosure containing air as in a normal auditorium as the artificial reverberation source, in Fig. 3 this source is constituted by a metallic or solid mass 25 of non-gaseous material having relatively great density compared to the density of air and of any suitable cubical or other shape if desired, but preferably having the form of a cylinder of substantially equal length and diameter, this short and broad configuration of the metallic body tending to broaden the resonance of the reverberation device. Various metals, alloys, and also non-metallic solids may be employed for the mass 25. For example, a suitable material is an alloy of approximately '78 per cent copper and 22 per cent tin.

Similarly to the reverberation device i i of Fig. 1, in accordance with my present invention, the metallic cylinder 25, whose diameter and length are of the same order of magnitude so that the standing wave pattern may simulate that of a large auditorium, is of materially reduced dimensions relative to the dimensions of a corresponding element which would be necessary to produce reverberation in the audio-signal without the carrier.

To cause the small metallic mass 25 to produce the desired reverberation effect, the high frequency carrier oscillations from oscillator ll modulated by the oscillations of signal audio-frequency from microphone l0 are impressed, through intermediate frequency stage 49, preferably on an energizing winding 26 or other suitable energizing means associated with a magnetostrictive element 21 secured to the metallic cylinder 25 at one face thereof.

To pick up the sound output of the reverberation device constituted by the small metallic cylinder 25, a similar magnetostrictive element 28 is secured to the opposite face of the cylinder and a pick-up winding 29 associated with the latter magnetostrictive element is connected to' the detector stage 22 which is connected through audio-amplifier stage 23 to the sound producing device or loud-speaker i2. In order to broaden the response of the magnetostrictive elements and therefore to broaden further the total resonance of the artificial reverberation system, the elements 21 and 28 are preferably constituted by members such as plates 30, 3| and 32, of different lengths.

In operation of the system illustrated in. Fig. 3, the energizing winding 26 induces audio-frequency signal-modulated sound carrier oscillations in magnetostrictive element 21 which impresses these modulated sound-carrier oscillations upon the metallic mass 25 to produce therein corresponding modulated carrier sound oscillations to which are added reverberation components of suitable characteristics. The resultant signal-modulated sound-carrier oscillations having the desired reverberation added thereto are transmitted to the magnetostrictive element 22 which induces corresponding electric oscillations in the pick-up winding 29 which in turn impresses the latter electric oscillations upon detector 22. As in the system of Fig. 1, in the detector 22 of Fig. 3 the audio-frequency electric signal containing the desired reverberation components is detected, and impressed through amplifler 23 on the sound producing device or loudspeaker l2 which reproduces the original audiofrequency sound signal but having added thereto the reverberation com; onents produced by the reverberation device 25 of small dimensions.

2,810,417 ystems illustrated in Figs. 4 and are ral similar in construction and operation e that of Fig. 8. the principal difference being tha whereas in Fig. 3 the'reverberation' device nents, in Fig. 4 the reverberation device is a long body such as a cylinder 32 in which the wave motion is approximately one dimensional or longitudinal. and in Fig. 5 the reverberation device is also a long cv bder 24 or the like but in which the magnetostrictive elements 25 and 36 are ar ranged at right angles to the cylinder to produce flexural vibrations with also a small amount of torsional vibration.

The system illustrated in Fig. 6 is similartc those of Figs. 3 to 5 except in the nature of the medium employed in the reverberation device. Instead of the metallic or solid masses of various shapes, in Fig. 6 the vibratable medium is a liquid 31 within a container 38 having walls of suitable form and material and having maximum sound reflection coeillcient, to provide desired reflecting surfaces for sound vibrations produced in the liquid. The liquid is arranged to be vibrated by the magnetostrictive element 39 and the resultant sound oscillations are received by the magnetostrictive element 40. the elements I! and 40 respectively extending through the container 38 on opposite sides thereof into contact with the liquid 31.

In the system illustrated in Fig. 7 the reverberation device comprised in the artificial reverberation system and designated by the numeral 4i may be constituted by a plurality of metallic cylinders 42 to 41 graduated in length and therefore difi'erently resonant, each cylinder having secured thereto magnetostrictive elements respectively at the opposite ends of the corresponding cylinders. The material of the cylinders may be any suitable solid, but is preferably the copper-tin alloy above mentioned. Preferably for each of the reverberation elements 42 to 41, a separate means is provided for generating the audio-signal modulated sound-carrier wave ap propriate to the given reverberation element. Thus for element 42 an oscillator 4! produces a carrier appropriate thereto which is modulated by the voice frequency from microphone ill and impressed through an intermediate amplifier stage 49 on the energizing winding 50 of the magnetostrictive driving element 5| secured to reverberation element 42. For another element as 41, as shown in the drawing, a separate oscillator 52 produces a carrier appropriate to the latter reverberation element and the latter carrier is likewise modulated by the voice frequency from microphone in and impressed through an amphfier stage 53 on the energizing winding 64 of the magnetostrictive driving element 55 of the device 41. It will be understood that similar separate driving circuits (not shown) are preferably provided for the other reverberation elements 42 to 46. 7

Likewise, separate pick-up circuits such as described hereinabove in connection with Fig. 3 are preferably provided for the reverberation elements 42 to 41, two of the latter circuits 58 and 51 for devices 42 and 41 respectively being illustrated in the drawing. The outputs of the pickaudio-frequency amplifier It and thence upon the sound producing device or loud-speaker I2.

Instead of the separate driving and pick-up means, a single oscillator and modulator and a single pick-up may be employed for all of the cylinders.

In operation of the system illustrated in Fig. '1, carrier signals each modulated by the audiofrequency signal are impressed on the different up circuits are preferably impressed upon an reverberation elements or cylinders 42 to 41.

Therefore, reverberant'sound is transmitted by each of the cylinders in accordance with the resonance characteristics of each cylinder. The

total band width produced by the system is the sum of the band width of the separate cylinders. Further, the reverberant audio-frequency signal is substantially increased over the like systems herein illustrated incorporating only one metallic body in the reverberation generating device. In order that the higher frequencies translated by the reverberation device 4| may have the same reverberation time as the lower frequencies, the relative proportion of copper and tin in the mate rialof which the cylinders are .composed may be varied progressively from the longest in the shortest cylinder.

' It will be seen that the various systems hereinabove described and embodying my invention are similar in organization and operation to a public address system, the voice or music impressed upon the microphone l0 being projected, with desired reverberation added thereto, from the sound reproducer or reproducers represented by the loud-speaker device l2. My invention is particularly well adapted to such public address system use since, by the addition of reverberation of proper characteristics easily and simply provided by the reverberation device of small dimensions, the reproduced voice or music is made to simulate to any desired degree to a listener even in the open air the reproduction of the voice or music as it would be presented to the listener in an auditorium or sound studio having reverberation characteristics but suited for the sound reproduction.

The invention, however, is in no sense limited to use in connection with a public address :ystem but may be readily adapted to a variety of other uses, for example, in broadcasting systems, phonographic apparatus, radio receivers and other like applications. Thus while I have described my invention herein in particular embodiments for purposes of illustration, it is to be understood that the invention is susceptible of various changes and modifications and that by the appended claims I intend to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In an artificial reverberation system. a reverberation device including a non-gaseous mass,

having relatively great density compared to the density of air, means to produce within said mass a superaudible carrier sound wave modulated by a voice sound wave, and means to recover from said voice modulated carrier wave within said mass said voice sound wave having added thereto the reverberation produced in said carrier wave within said enclosure.

3. In an artificial reverberation'system, a reverberation device including a metallic mass, means to impress upon said mass a superaudible carrier sound wave modulated by an audio frequency sound wave, said mass being small relative to an equivalent mass having desired reverberation characteristics for said audio wave only, andmeans to detect from said first-named mass said audio frequency sound wave having added thereto the reverberation produced by said firstnamed mass.

4. In an artificial reverberation system, a reverberation device including a container having a liquid therein, means to impress upon said liquid a superaudible carrier sound wave modulated by an audio frequency sound wave. said liquid being of small mass relative to an equivalent mass of liquid having desired reverberation characteristics for said audio wave only. and means to detect from said first-named liquid said audio frequency sound wave having added thereto the reverberation produced by said firstnamed liquid.

6. In an artificial reverberation system, a plurality of metallic members of diiferent resonance characteristics, means to generate an audio frequency sound wave, means to impress upon each of said metallic members a superaudible carrier sound wave modulated by said audio frequency sound wave, and means to detect from said resonant metal members said audio frequency sound wave having added thereto the sum of the reverberation components produced by said audio modulated sound wave insaid metallic members.

'WILLIAM D. PHELPS.

CERTIFICATE OF CORRECTION. Patent No. 2,518,h17.' Hey 1;, 15h

. wILLIAn D. PHELPS.

It is herebycertified the't error appears in the printed specification of the above numbered patent requiring correction as follows: Page 3, second column, line 75-, claim 2, for "In a reverberation device including a mass" d Inan artificial reverberation system, a reverberation device including a o and that the said Letters Patent should .be read with this correction therein that the same may conform 'to the record of the case in the Patent Office.

si hed am sealed this 22nd da of June, A. n. 19h}.

Henry Van Arsdele, (Seal) Acting-Commiesioner of Patents.

CERTIFICATE or CORRECTION.

Patent NO. 4 h, WILLIAM D. PHELPS.

It is hereby'certified that error appears in the printed specification of the above'numbered patent requiring correction as follows: Page 3, sec- ,ond column, line 75-, claim 2, for "In a. reverberation device including a i d Inan artificial reverberation system, a reverberation device including a m -'1; and that the said Letters Patent should .be read with this correction thereinthat the same may conform to the record of the case in the Patent Office.

Signed and sealed this 22nd da of June, A. D. 191;

Henry Van Arsdale, (Seal) Acting-Cmmnis sioner of Patents.

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