Title:
Artificial reverberation system
United States Patent 2318417


Abstract:
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 sound signals having initially included therein no reverberstion...



Inventors:
Phelps, William D.
Application Number:
US44547142A
Publication Date:
05/04/1943
Filing Date:
06/02/1942
Assignee:
GEN ELECTRIC
Primary Class:
Other Classes:
84/DIG.26, 333/201
International Classes:
G10K15/10
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Description:

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 sound signals having initially included therein no reverberstion components or aeglgible amount. thereof.

The general object of the invention is to provide improved devices for thus producing and adding artificial reverberation which are simple and efficient and which, in particular, are of dimensions preferably small relative to corresponding means and devices hitherto employed or suggested for 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 therein, next generating within the reverberation device of reduced dimensions a superaudible carrier sound frequency which is modulated by the above-mentioned unreverberated sound slignas frequency, and finally 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 suer-audible sound wave sond as a carrier for the audio-frequency sound wave, reverberation effects 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 car- 4 rier 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 de- 5a vices, 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 56 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; Pig. 2 Is a modification similar to the system of Mg. 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; igs. 4 and 5 are further modifications similar to that of Fig. 3; Fg. 6 is a modification employing a liquid element as the reverberation device; and Fg. 7 is a modification employing a plurality of differently resonant metallic elements in the re0 verberation device.

In the system illustrated in Pig. 1, the numeral 10 designates an audio-frequency sound signal device such as a microphone or the like, numeral II designates a small reverberation device or en5 closure 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 im0 pressed upon and translated by the microphone 10, and numeral 12 designates a sound signal output device such as a loud-speaker. The enclosure II is Preferably provided with means for adjusting the reverberation characteristics there5 of comprising, for example, a movable wall Is 2 2,81 for varying the volume of enclosed air, windows or free openings 14, adjustable shutters 1I for varying the area of the openings, and sound absorbent material 16, if desired, over certain areas of the inner wall 'surfaces.

To utilize the relatively small auditorium model I I as a source of artificial reverberation to be added to the original audio-frequency sound signal, a source 17 of electric oscillations of ultrasonic or superaudible frequency, for example of thirty-thousand cycles per second, is provided, connected to a modulator 18 to which the microphone 10 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 mounted at a desired point within the reverberation device or enclosure 11. At another point within the enclosure is mounted a microphone or like pick-up device 21 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 12.

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 17 is modulated by the audio-frequency electric signal oscillations from microphone 10. The modulated electric signal is amplified in the amplifier stages 19 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 21 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 12 which reproduces the original audiofrequency sound signal with the addition thereto of the reverberation which was produced, within the enclosure 11, in the modulated superaudible carrier sound wave.

The sound producing and reproducing devices 20 and 21 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 illustrated therein are the same as for the system of Fig. 1 except that in 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 artificial reverberation means and is impressed together with the signal detected from microphone 21 upon the sound producing device or loudspeaker 12 as by connection of the output oi microphone 10 to the audio-amplifier 23 through suitable connections 24.

Referring to Fig. 3, the system therein illus. trated may be similar in general to those of Figs 1 and 2 except in the construction and manne] of operation of the reverberation device em. 8,417 ployed. 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 II 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 26 to produce the desired reverberation effect, the high frequency carrier oscillations from oscillator IT modulated by the oscillations of signal audio-frequency from microphone 10 are impressed, through intermediate frequency stage 19, preferably on an energizing winding 26 or other suitable energizing means associated with a magnetostrictive element 27 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 12. 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, 31 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 28 which induces corresponding electric oscillations in the pick-up winding 29 which in turn impresses the latter electric oscillations upon deS tector 22. As in the system of Fig. 1, in the detector 22 of Fg. 3 the audio-frequency electric f signal containing the desired reverberation comS70 ponents is detected, and impressed through amplifier 23 on the sound producing device or loudspeaker 12 which reproduces the original audiofrequency sound signal but having added thereto r the reverberation com: onents produced by the - 75 reverberation device 25 of small dimensions.

3,818 The systems illustrated in Figs. 4 and 5 are In general similar in construction and operation to that of fig. 3, the principal difference being that, whereas in ig. 3 the reverberation device is in the form of a short and relatively broad body and preferably a cylinder whose length and diameter are of the same order of magnitpde and in which the reverberation waves may be a combination of torsional and longitudinal components, in Fig. 4 the reverberation device is a long 1( body such as a cylinder 33 in which the wave motion is approximately one dimensional or longitudinal, and in Fig. 5 the reverberation device is also a long cylinder 34 or the like but in which the magnetostrictive elements 35 and 36 are ar- 1~ 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 similar to those of igs. 3 to 5 except in the nature of the 2( medium employed in the reverberation device.

Instead of the metallic or solid masses of various shapes, in Pig. 6 the vibratable medium is a liquid 31 within a container 38 having walls of suitable form and material and having maximum sound reflection coefficient, 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 39 and 40 respectively extending through the container 38 on opposite sides thereof into contact with the liquid 37.

In the system illustrated in ig. 7 the reverberation device comprised in the artificial reverberation system and designated by the numeral 41 may be constituted by a plurality of metallic cylinders 42 to 47 graduated in length and therefore differently 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 47, a separate means is provided for generating the audio-signal-modulated sound-carrier wave appropriate to the given reverberation element.

Thus for element 42 an oscillator 43 produces a carrier appropriate thereto which is modulated by the voice frequency from microphone 10 and impressed through an intermediate amplifier stage 49 on the energizing winding 50 of the magnetostrictive driving element 61 secured to reverberation element 42. For another element as 47, 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 10 and impressed through an amplifier stage 53 on the energizing winding 54 of the magnetostrictive driving element 55 of the device 47. It will be understood that similar separate driving circuits (not shown) are preferably provided for the other reverberation elements 43 to 4s.

Likewise, separate pick-up circuits such as described hereinabove in connection with Fig. 3 70 are preferably provided for the reverberation elements 42 to 41, two of the latter circuits 56 and 5B for devices 42 and 47 respectively being illustrated in the drawing. The outputs of the pickup circuits are preferably impressed upon an ,417 3 audio-frequency amplifier I8 and thence upon the sound producing device or loud-speaker 12.

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

In operation of the system illustrated in Fig. 7, carrier signals each modulated by the audiofrequency signal are impressed on the different 0 reverberation elements or cylinders 42 to 47.

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 Ssum 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.

SIn order that the higher frequencies translated by the reverberation device 41 may have the same reverberation time as the lower frequencies, the relative proportion of copper and tin in the material of which the cylinders are composed may be Svaried progressively from the longest to 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 10 being projected, with desired reverberation added thereto, from the sound reproducer or reproducers represented by the loud-speaker device 12. 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 Sto 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 3ystem 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, means to produce within said device a superaudible carrier sound wave modulated by an audio frequency sound wave, said device being of reduced dimensions relative to the dimensions of an equivalent reverberation device having desired reverberation characteristics when said audio frequency sound wave only is produced therein, and means to detect from said audio modulated carrier wave within said device said audio frequency sound wave having added thereto the reverberation produced in said modulated wave by said reverberation device.

2. In a reverberation device including a mass having relatively great density compared to the density of air, means to produce within said mass a superapdible 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, and means 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.

5. In an artificial reverberation system, a plurality of metallic members of different 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 in said metallic members.

WILLIAM D. PHELPS.

CERTIFICATE OF CORRECTION.

Patent No. 2,518,417. May 4, 14^3.

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, second column, line 75, claim 2, for "In a reverberation device including a mass" read -- In an artificial reverberation system, a reverberation device including a mass--; 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.

Signed and sealed this 22nd day of June, A. D. 1943.

Henry Van Arsdale, (Seal) Acting Coaissioner of Patents.

CERTIFICATE OF CORRECTION.

Patent No. 2,518,417. May 4, 193.

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, second column, line 75, claim 2, for "In a reverberation device including a mass" read -- In an artificial reverberation system, a reverberation device including a mass--; 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.

Signed and sealed this 22nd day of June, A. D. 19.3.

Henry Van Arsdale, (Seal) Acting Commissioner of Patents.