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Publication numberUS2942070 A
Publication typeGrant
Publication dateJun 21, 1960
Filing dateMar 26, 1954
Priority dateMar 26, 1954
Publication numberUS 2942070 A, US 2942070A, US-A-2942070, US2942070 A, US2942070A
InventorsHammond Laurens, John M Hanert, Donald R Kern
Original AssigneeHammond Organ Co
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Means for binaural hearing
US 2942070 A
Abstract  available in
Images(1)
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Claims  available in
Description  (OCR text may contain errors)

June 21, 1960 L. HAMMOND 2,942,070

MEANS FOR BINAURAI. HEARING Filed March 26, 1954 50' AMPLI-O-I-OM 26 0 PIER. o-----ol ADJUsTABLE rm IEEVEEBEE- ATTENUATOE 5 UR E I ATON AMPL'- I ..E- L52 I r APPARATUS L HER 2 ELECTRICAL 2 scum: AMPLI' I 55 SIGNALS 6 L xffigs I=IEE 0 L 1 E7 X APPARATUS E: ADJUSTABLE Cf AMPLI cg TTENIJATOE Z4 3 FIEJZ a I L55 a? F 5:

EEvEIzsEEw, AMPLI- ATION c P SOURCE APPARATUS ELECTRICAL 5OUND sIpNALs OI Io I umonmm UZCOU! I so "INF ill

PICKUP (WITH DELAY) QMEANS FoIz INTRODUCING DELAY WITH EESLILTANT VARIATIONS IN AMPLITUDE RESPONSE IN THE AUDIO I FREQUENCY SPECTRUM WHEN COMBINED WITH IoTHE DIRECT sIeINAL I,

Min-

5AM E A5 ABOVE MEANS FOR BINAURAL HEARING Laurens Hammond, Chicago, John M. Hanert, Des Plaines, and Donald R. Kern, Chicago, Ill., as'signors to Hammond Organ Company, Chicago, Ill., a corporation of Delaware Filed Mar. 26, 1954, Ser. No. 418,865

18 Claims. or. 119-1001 Patented June 21 harmonic analyzer, or like a reed type frequency meter, and electrical impulses are transmitted to the brain cor: responding to the amplitudes of the various frequencies which are present in the sounds being heard. The

analyses produced by the two cars, of course, will be the source of the sound, but rather to have the listener 1 perceive the sound as binaurally omnidirectional; The effect obtained is very unique, possessing to a marked degree the highly desirable property of music'heard in-a' large auditorium, in which all of the sounds reach the lis-' tener by an indefinitely great number of paths. There is apparently no sound heard. through a direct path and therefore there are no positive sensations of definite sound localization. I The invention may be employed using any of a variety of sources of electrical tone signals,such as electric organs and similar electrical musical instruments, radio receivers, and various forms of recorded music, such asmusic recorded on phonograph records, on magnetic wire or tape',.'on film, etc.

We have discovered that binaural hearing, or stereophonic perception, is largely caused by the differences in the amplitude analysis of the sound, taken over the audio frequency range, as its reaches the listener's two cars. If a sound originates at some distance from the listener it is well-known that violent amplitude distortions, or standing wave patterns, due to the room's acoustic reflections, will be present. The number of upsets or variations in the amplitude response, taken over the audio frequency spectrum, is largely controlled by the distance and the number of reflectingpaths by which the sound reaches the, two cars. If it is assumed that the original source of soundis emitting uniform energy'at all the desired signalfrequencies, the car will not hear-the same energy at all frequencies due to the phase addition and cancellation efiects of sounds reaching the ear through acoustic paths of different lengths. When the source of sound isat a distance which is large in comparison with the wave length of the lowest frequency being transmitted, cancellations or additions may occur at any of the frequenciesbeing emitted.

radically different for a sound coming from a distant source because the various paths by which the sound reaches the two ears can be radically different at many different frequencies. Hearing at a distance, therefore,- results in a great number of different amplitude responses over the'audio frequency spectrum.

If the source is very close, then the analyses by the two cars will closely coincide and the brain interprets this" as a sound which is relatively close to the listener. If, on the other hand, the analyses by the two ears discloses many different and conflicting amplitude responses, the brain will interpret these many opposing upsets as being caused by a source which is relatively distant fromthe eat.

It is well-known in music that the most desirable conditions for pleasurable listening involve relatively long distances like 40 and 50 feet, and that it is undesirable to" listen-for instance, to a violin-in a small closet-like enclosure. The apparatus of our invention is designed to produce a pleasing illusion of listening in a large enclosure despite the fact that the actual source of sound is directly adjacent the listener's ears. The method which we em ploy for creating'this binaural illusion is to modify the signals occurring at the two ears in such a way as toproduce many upsets in amplitude over the audio frequency spectrum in each of a pair of electroacoustic transducers," such as earphones, respectively positioned at the two cars, so thatthe sound emitted by one transducer is heard-predominantly by one of the listeners ears and that the sound emitted by the other transducer is heard predominantly bythe other ear of the listener, and further, to cause these amplitude variations to occur at diflerent frequencies for the two earphones. By so doing, we have found that it is possible to create an amazingly real quality of stereophonic perception, namely, the effect of hearing sound in a large auditorium having ideal acoustical properties for listening to music. 1 -When listening with the apparatus of our invention, the

' listener is unable to acknowledge the fact that the sound is originating at his ears but rather perceives the phe-- nomena as being one of hearing many sources of sound remotely located in a large-auditorium. 'Thus, it is pos sible to createa very satisfying binaural perception with any form of music or speech which may originally beer a -monaura l or single channel character .as, for example, the signals from a radio receiver, a phonograph pickup, or the signals from an electrical .musical-instru ment. With the apparatus of our invention, if the source of sound is disconnected from either earphone the carat the other phone perceives the source as being immediatelyv adjacent that car. If, however, the source is reconnected so that the sound is present at both ears, then the listener perceives the source of sound as. being remotelylocatedlf the source is emitting a random noise spectrum in suitable harmonic analyzer will disclose, a large number a of upsets or variations in amplitude response at the various-portions of the audio frequency spectrum being analyzed. Flhe greater the distance between the source and the microphone, the greater will be the number of these amplitude upsets within the: gamut ,of the audio spectrum.-.-

I Inbinaural perception-ofsound one judge, ina general way, the distance of-a' source of sound by means of the two cars. It is a well-known auditory phenomenon in many parts of a large auditorium-like enclosure which physically does not exist but whose dimensions acoustic properties are forcefully suggested. 5

The apparatus may be such that although for eachear; considered individually, the frequency response upsets might be excessive and undesirable for listeningto music; this is not true when both earphones-are energized in-the' manner to be described. This is partly-because that, while the uniformity. of energy over the audio: frequency spectrum is purposely upset in different ways at the earphones,

' the resultant perception, when both earphones are used, is

oneofhigh fidelity in amplitude responsedue to the summation effect in the brain of the signals received by the two cars. 'Thus, while the amplitude upsets are iiiten that each of the ears functions in a manner similar toja tionally provided for the purpose of achieving a stereo phonic acoustic perception they are not present in the final composite acoustic perception which is due to hearing with both ears.

For example, the apparatus of this invention is intentionally effective to attenuate a certain frequency in one car while either statistically, or by inherent circuitry. to make this signal present in the other car thus insuring its presence in the final composite signal due to the contributions made by both ears.

While the apparatus of the invention utilizes a time delay or uses reverberation apparatus for causing amplitude upsets due to the addition of signals having differing phases, such phase shifting apparatus does not result in a sequential perception of the sound by the two ears, that is, the sound appears to start and cease at substantially the same instants in both of the listeners ears. This, of course, is highly desirable from a musical standpoint as it has been found that delay apparatus which introduces the sound in one ear after it has been introduced in the other car is highly unsatisfactory and tiring to the listener. I It is therefore the object of the invention to provide methods and means for greatly improving the pleasure of listening to monaural music in accordance with the principles above set forth.

Other objects will appear from the following description, reference being had to the accompanying draw x in which:

- Fig. l is a schematic wiring and block diagram showing the preferred form of the invention;

Fig. 2 is a similar diagram of'a modified form of the invention;

Fig. 3 is a similar diagram of a further modification of the invention; and

Fig. 4 is a similar diagram of another modification.

Referring to Fig. l, a source 10 of electrical sound signals may comprise an electric organ, phonograph, radio receiver, or any other source of sound, particularly music, in the form of an electrical signal and has output terminals 11 and 1-2.

The output terminal 11 of the source is connected to a point of constant potential, indicated as ground. The' output terminal 12 of this source is connected through an adjustable resistor R16 to a reverberation device or apparatus 18. The terminal 12 is similarly connected through an adjustable resistor R17 to a reverberation appnratus 19. The input circuits of the reverberation devices are shown as including coils 24 and 25 which may be the primaries of input transformers, or may be the voice coil windings of electroacoustic transducers. 'Ihese coils are respectively connected between the resistors R16 and R17 and ground.

The outputs of the reveberation devices 18 and 19 are coupled to amplifiers 26 and 27, and the outputs of the letter are coupled to mixers 28 and 29.

The output of the source 10 is also connected to the input of amplifiers 30 and 31 and the outputs of the latter are respectively connected to the mixers 28 and 29. Each, or at least one, of the mixers may be provided with an adjustable attenuator 32, 33. The output of the mixer 28 is connected to one electroacoustic transducer shown as an earphone 34 while the output of the mixer 29 is connected to the other transducer earphone 35 of a pair.

The reverberation devices 18 and 19 are preferably of the type shown in the patent to Laurens Hammond No. 2,230,836, omitting the means providing a direct path for the transmission of the signal from the source to the speaker shown in said patent, namely, omitting the circuits including the adjustable resistors 24. However, the dcvioes 18 and 19 may be any type of apparatus, (acoustic, recording and play-back, etc.) which will convert nonreverberative input signals into reverberative output sig nlls. The adjustable attenuators 32 and 33 are provided so thnt suitable compensation may be made when the app-mm: is used by'those whose acuity of hearing of one elf dificrs from that of the other.

It will be apparent that each earphone receives a direct signal from the source in addition to a signal from the source into which reverberative effects have been introduced. Due to unavoidable differences in the frequency response characteristics of the two devices 18 and 19 the sound at the two cars will be different. Certain frequencies will be sounded with greater intensity at one ear than at the other. Assuming that the attenuators 32 and 33 and the mixers 28 and 29 are adjusted properly for a normal listener, the total energy of the signal supplied to the two earphones 34 and 35 will be the same but certain frequencies in the audio range will be of higher amplitude at one earphone and at lower amplitude at the other earphone. The frequency response pattern is random so that the overall effect on the listener is that he perceives the sound as being produced in a large reverberative room in which the sound reaches his ears through a large number of different paths, and in which, due to the spaced position of his two eardrums, certain frequencies are attenuated as heard by one car, while other difierent frequencies in the sound heard by the other car are attenuated.

Due to the delay introduced by the reverberation 66! I vices, at the commencement of a tone only the direct signal transmitted through the amplifiers and 31 will be supplied to the earphones 34 and respectively. Then after a very small fraction of a second the rever- 4 berative signal will be added until, as the tone signal mpplied by the source 10 stops, only the reverberative sigmh will be supplied to the earphones. This latter fact also adds to the three dimensional or stereophonic effect.

The mixers 28 and 29 are preferably provided will manually operable controls, in addition to the adjustable resistors R16 and R17, whereby the ratios of the reverberative relative to the direct signals supplied to the two earphones may be varied to suit the wishes of the listener.

For the purpose of maintaining bilateral symmetry in the illustration, two amplifiers 30 and 31 are shown. It is apparent that one of these amplifiers could be omitted and its output supplied to both mixers 28 and 29 for providing the direct signal for both earphones.

The objects of the invention may be achieved by utilizing the less costly and more simple modified form of the invention shown in Fig. 2. In this form of the inven tion the source 10 has one of its output terminals connected to ground and its other terminal connected to a reverberation apparatus 42 through a potentiometer RM. The other input terminal of the reverberation apparatus is connected to ground. The output of the apparatus 42 is coupled to an amplifier 46 and the output of the latter is supplied to the primary of an output transformer 48. The secondary 50 of this transformer has its end terminals connected respectively to one terminal of the pair of terminals of earphones 52, 53 by conductors 54 and 56 respectively. The other terminals of the earphones are connected to ground. The secondary winding 50 of the transformer 48 has a center tap 56 which is connected to the sliding contactor of a voltage divider RS7 which is connected across the output terminals of the source 10.

A plurality of capacitors CS8 are adapted to be connected cumulatively between the conductors 54 and 55 by a rotary switch member 60. When this switch member is moved counterclockwise from the position shown in full lines to the position shown in dotted lines, it makes contact with a contactor 62 forming part of this switch. thereby to connect conductors 54 and 55, and thus shunt the reverberative portion of the signal from the earphones whenever the binaural eflect is not desired. The ca-' pacitors C58 and switch 60 operate as a tone control to reduce the amplitudes of the higher frequencies.

In this form of the invention the reverberative signal will be heard in the earphones in opposite polarity so that while the reverberative signal is adding to the dim signal in one earphone 52, his subtracting from the direct signalintheearpbonefi andviceversa. Becausethern is only one means for introducing the reverberation effect, the effect of having different frequency response characteristics in the reverberative tones transmitted to the two ears is lost during the decay period after the direct signal ceases, but in steady state the results obtainable by the apparatus of Fig. 2 are quite similar to those obtained by the apparatus shown in Fig. 1. Either the direct or the reverberative signal may be supplied to the earphones in the push-pull manner.

The system shown in Fig. 3 is quite similar to that shown in Fig. 2 except that the source of sound comprises a sound record 70 which may be a phonograph divider R76 is connected .to the center tap of an output transformer 48. This transformer forms part of an output system whichmay be the same as that shown in Fig. 2. Similar reference characters have therefore been applied to corresponding parts and their description will not be repeated.

A second pickup 78' is coupled to an amplifier 80, the output terminals of which are connected to the'ends of the primary winding of transformer 48. The pickups 72 and 78 are physically'spaced sufiiciently in the direction of the movement of the soundrecord 70 so that the delay introduced in the signal picked up by pickup 78 will be in'the order of 70 milliseconds, and the pickups are preferably mounted so that their spacing in the direction ofthe movement of the sound record may be changed at will to suit, the discriminatory judgment of the listener. Because it is not essential'that either the direct or the delayed signals supplied to the two earphones be introduced in opposite polarity, it is possible to accomplish the objects of the invention by the apparatus shown in Fig. 4. In this form of the invention the signals from the source 90 are supplied in parallel to two devices 91 and 92 for introducing delay in the signals, with resultant variations in amplitude response in the audio frequencyspectrum when the output thereof is combined with signals transmittcd directly to the earphones.

- The outputs of the devices 91 and 92 are respectively connected to the earphones 93 and 94 through adjustable decoupling impedanoes' R95 and R96, while the signal from the source 90 is transmitted directly to theearphones 93 and 94 through adjustable decoupling resistors R97 and R98 respectively. The devices 91 and 92 for introducing the delay may be similar, but should not be identical, so that the twoears perceive the tone dif-' ferently due to the different amplitude response characteristics of the two signals supplied to the earphones.

The essence of the invention resides in improving the auditory reception of sounds derived from a single source as electrical signals in which pairs of transmission channels have their inputs coupled to the source and in which at least one of the channels includes means to introduce variations in amplitude response in the sound transmitted thereby and in which a pair of earphones are coupled respectively to the outputs of the transmission channels .are employed to translate the electrical signals into sound. The delay which is provided for in the several forms .of the invention may be introduced by an artificial line or any other suitable device which produces substantial It'will be clearto those skilled in the art that, in each of the embodiments, various types of tone and volume .controls maybe employed in conjunction with the amplifiers and mixers, in addition to those shown. and

described.

Vhile we have shown and described particular embodiphase shift of the signal, such that when superimposed on i a earphone received through the third path.

anneal invention. We thereforedesire, by the following claims,

to include within the scope of our invention all such similar and modified forms of the apparatus disclosed, by which substantially the results of the invention may be obtained by the use of substantially thesame or equivalent means. In some of the claims 'the word groun is used. This is intended to mean any point of fixed potential.

We claim:

1. Apparatus for improving the auditory receptionof sounds in the form of electrical signals derived from a single source, comprising a reverberation apparatus coupled to the source, an amplifier coupled to the output of the reverberation apparatus, an output transformer having a primary winding connected to the output of the amplifier and having a secondary winding provided with a center tap, a pair of earphones each having two ter minals, means connecting one terminal of each earphone to'one terminal of the source, and means connecting the other terminals of the earphones respectively to the end terminalsof the transformer secondary winding.

' 2' The combination of a single source of musical tone signals, apair of earphones, means for transmittinga signal derived from said source to eachof said earphones in opposite polarity, additional means for transmitting a signal from the source to each of the earphones in the same polarity, and means'for delayingthfe signal transmitted through one of saidnansiniaing means. J

"3. Thecombinat'ion .ofa single source of musiealton e signals, a pair of earphones,l;mean's for tran'sm i'tting a. signal derived from said source to each of said earphones in opposite phasq additional means. for transmitting a signal from the source to the earphones in the same phase, means for adding reverberative signals to the signal transmitted through one of said transmitting means, and means for'adju'sting the relative amplitudes of the signals supplied to the two earphones.

4. The combination of a single source of musical tone signals, a pair of earphones, means for transmitting a signal derived from said source to each of-said earphones in opposite polarity, additional means for transmitting a signal from the source to each of the earphones in the same polarity, and means for causing'a phase shift in the signals transmitted through one of said transmitting means. h

5. Thecombination of a musical tone signal source, a pair of earphones comprising a first earphone and a second earphone, means forming first and second signal transmitting paths coupling the source to the first earphone, means forming third and fourth signal transmitting paths coupling the source to the second earphone, means inthe first signal transmitting path to introduce delay with resultant variations in amplitude response the audio frequency spectrum and combined at'the, first earphone with the signal transmitted through the second path, and means included in the thirdsignal transmitting path to introduce a slightlydifferent delay with resultant different variations in' amplitude response in the audio frequency spectrum when the signal is combined at the second earphone with the signal transmitted through the fourth path. v 6.. The combination set forth in claim 5 in which means are provided to cause the signal at the first earphone received. through the first path to be of opposite polarity with respect to the polarity of the signal at the second 7.; The combination of a musical tone signalj source, a pair of earphones comprising a first earphone and a second earphone, means forming a first signal transmitting path coupling the source to the first earphone, means formingja'second signal transmitting path coupling the sourcetothe first earphone, means forming third" nd fourth signal transmission paths coupling the source to thesecond earphone, means to cause the signal transmitted through the first and third paths to be received at the earphone in opposite polarity, and means in the second and 'fourth signal transmitting paths to introduce delay witl't resultant variations in amplitude response when combined with the signals transmitted through the first and third paths.

8; The combination of a single source of audio frequency' signals, a pair of earphones, means for delaying the transmission of audio frequency signals coupled between the source and one earphone, a second means for delaying the transmission of audio frequency signals coupled between the source and the other earphone, and means coupling the source to both earphones, the two means for delaying the signals being sufiiciently different to produce different frequency response characteristics in the two earphones.

9. Apparatus for reproducing sound from a moving record comprising, a pair of pickups cooperable with the same sound track on the record and spaced from one another in the direction of movement of the record, the spacing being sufiicient that the signal at one of the pickups will be delayed with respect to the signal at the other pickup by an interval in the order of seventy milliseconds, a pair of earphones, and means coupling each of the pickups to each of the earphones, the coupling means for one of the pickups including means for one of the pickups including means to cause the signals therefrom to be received at the earphones in opposite polarity.

10. Apparatus for improving the auditory reception of sounds derived from a single source, comprising a reverberation apparatus coupled to the source, an amplifier coupled to the output of the reverberation apparatus, an output transformer having a primary winding connected to the output of the amplifier and having a secondary winding provided with a center tap, a pair of electroacoustic transducers each having two terminals and positioned that a listener can receive sound in each car from one of said transducers to the practical exclusion of sound from the other of said transducers, means connecting one terminal of each of said transducers to one terminal of the source, and means connecting the other terminals of the transducers respectively to the end terminals of the transformer secondary winding.

11. The combination of a single source of musical tone signals, a pair of electroacoustic transducers positioned so that a listener can receive sound in each ear from one of said transducers to the practical exclusion of sound from the other otsaid transducers, means for transmitting a signal derived from said source to each of said transducers in opposite phase, additional means for transmitting a signal from the source to the transducers in the same phase, means for adding reverberation to the signal transmitted through one of said transmitting means, and means for adjusting the relative amplitudes of the signals supplied to the two transducers.

12. The combination of a single source of electrical musical tone signals, a pair of electroacoustic transducers positioned so that a listener can receive sound in each car from one of said transducers to the practical exclusion of sound from the other of said transducers, means for transmitting a signal derived from said source to each of said transducers in opposite polarity, additional means for transmitting a signal from the source to each of said transducers in the same polarity, and means for causing a substantial phase shift in the signals transmitted through one of said transmitting means.

13. An apparatus for improving the auditory reception of sounds derived from a source as a single electrical signal, comprising a pair of signal transmission channels having their inputs coupled to the source, at least one of said channels including reverberative means to introduce variations in frequency response in the sound signals transmitted thereby when combined with signals from the 8 4 source, a pair of elcctroacoustic transducers positioned so that a listener may hear sound in one car predominantly from one of the transducers and in the other car predominantly from the other of said transducers, means coupling both transducers to the source, and means coupling the transducers respectively to the outputs of the transmission channels.

14. An apparatus for improving the auditory reception of sounds derived from a source as a single electrical signal, comprising a pair of signal transmission channels having their input coupled to the source, at least one of said channels including means to introduce a time delay in the transmission of the signal of an order of seventy milliseconds, thercby to cause variations in frequency response in the sound signals transmitted thereby when combined with signals from the source, a pair of electroacoustic transducers positioned so that a listener may hear sound in one ear predominantly from one of the transducers and in the other car predominantly from the other of said transducers, means coupling both transducers to the source, and means coupling the transducers respectively to the outputs of the transmission channels.

15. An apparatus for improving the auditory reception of sounds derived from a source as a single electrical signal, comprising a pair of signal transmission channels having their inputs coupled to the source, at least one of said channels including means to introduce variations in frequency response in the sound signals transmitted thereby when combined with signals from the source, a pair of electroacoustic transducers positioned so that a listener will hear sound in one ear predominantly from one of the transducers and in the other car predominantly from the other of said transducers, a pair of means coupling both transducers to the output of one of the transmission channels, another pair of means coupling the transducers to the outputs of the other transmission channel, one of said pairs of coupling means supplying the signals to the transducers in the same polarity and the other pair of coupling means supplying signals to the transducers in opposite polarity for a substantial portion of the time that the signal is being transmitted.

16. An apparatus for improving the auditory reception of sound derived from a single sound record, a pair of pickups spaced along the sound record a distance sufficient to introduce a delay in the order of seventy milliseconds in the electrical sound signals from one pickup relative to those from the other pickup, a pair of signal transmission channels having their inputs coupled to the pickups, respectively, a pair of clectroacoustic transducers positioned so that a listener may hear sound in one ear predominantly from one of the transducers and in the other car predominantly from the other of said transducers, means coupling one pickup to the transducers in the same polarity and means coupling the other pickup to the transducers in opposed polarity.

17. An apparatus for improving the auditory reception of sounds derived from a single source as electrical signals, comprising a pair of signal transmission channels having their inputs coupled to the source, each of said channels including reverberative means to introduce variations in frequency response in the sound signals transmitted thereby when combined with signals from the source, a pair of electroacoustic transducers positioned so that a listener may hear sound in one ear predominantly from one of the transducers and in the other car predominantly from the other of said transducers, means coupling both transducers to the source, and means coupling the transducers respectively to the outputs of the transmission channels.

18. in combination with a primary single source of electrical musical sound signals, time delay introducing means coupled to the primary source and having its output constituting a secondary source of musical sound signals, a pair of electroacoustic translating means, means coupling t e primary source to each translating means, means coupling the secondary source to each translating means, and means to reverse the polarity of the signals from one of the sources to supply such signals in opposite polarity to the two electroacoustic translating means.

References Cited in the file of this patent 10 Snow Nov. 15, 1938 Hammond Feb. 4, 1941 Begun Aug. 24, 1943 Hayes Apr. 29, 1947 Olson Jan. 3, 1950 Boelens et a1 Dec. 28, 1954 Fine Aug. 2, 1955

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Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3062923 *Mar 5, 1959Nov 6, 1962Eddie S TubinAdjustable reverberation device with muting switch
US3068319 *Nov 4, 1960Dec 11, 1962John L FletcherAcoustic reflex ear protective system
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US3795770 *Aug 30, 1971Mar 5, 1974Nippon Musical Instruments MfgAcoustical filtration method and apparatus for obtaining instrumental tones
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Classifications
U.S. Classification369/60.1, 381/63, 381/17, 84/DIG.260, 369/87
International ClassificationH04S5/00
Cooperative ClassificationY10S84/26, H04S5/00
European ClassificationH04S5/00