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Publication numberUS2904632 A
Publication typeGrant
Publication dateSep 15, 1959
Filing dateJul 28, 1958
Priority dateJul 28, 1958
Publication numberUS 2904632 A, US 2904632A, US-A-2904632, US2904632 A, US2904632A
InventorsLevy Sidney E
Original AssigneeUniv Loudspeakers Inc
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Stereophonic sound propagation system
US 2904632 A
Abstract  available in
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Claims  available in
Description  (OCR text may contain errors)

Sept. 15,

LEVY

ATTORNEY considered practical.

United States Patent() srERuorrroNlc SOUND rRorAGATIoN SYSTEM ,Sidney E. Levy, White Plains, N.Y., -assignor, by direct .and -mesne assignments, to University Loudspeakers, Inc., White '-Plains, N.Y., a corporation of New York -Applicationf'ruly .28, 1-9ss,-seriai No. A751,557 1'9 Claims. (Cl'. 179-1) advent of the dual track magnetic tape recorder, the

provision of stereo'phonic sound in the home was not Such tape recorders immediately provided the'possibility of :high `quality stereophonic recordings which` provide-a convenient source of program lmaterial, Aitlthenonly beingnecessa'ry to provide suitable felectronic equipment, including audio amplifiers and a lsuitable loudspeaker system'in order to provide acceptable s'tereophonic sound in the home which represents a very --marked improvement yover the old and 'conventional methods "of sound reproduction. There have also recently become commercially available stereophonic disk recordings'which mayI likewise be utilized with 'the same electronic lequipment as Vis used with magnetic tape recorders and Iconsequently there-is now adequate lprovisions Afor fsources of :program material and the. main .problems reside in -theV design and installation of the electronic and loudspeaker equipment in the location to be utilized. It is also to be noted that stereophonic program `material is now occasionally available by means of radio broadcasts -utilizingboth a'nd FMwith the result 'that AM land "FM :receivers would `supply thefprogram material, rather than tapeand'disk recordings..

In-the installation kand -designof stereophonic sound propagation systems, manyfacts and problems' must be -taken into consideration and sin'ce lthe design and construction of audio amplifiers has now reached afhigh state :of perfection, theprimar-y lconcern is with the ydesign and installation of proper loudspeaker equipment. "In a stereophonic sound propagation system,'the sound 'must emanate from lat least two Vspaced points and this fact rimmediately introduces `the Yquestion of vsize of the installation as well yas-the shape and size ofthe room `in which the equipment is to be installed andfurthermora Asince yhigh qualityloudspeakers are relatively costly,` the number of such'speakers must be .kept to va minimum consistent with providing the sound qualityy desired.

vHeretofore, it -has been -usually customary-.to utilize either a full frequency range loudspeaker at A:each loudspeaker location or to utilize a multi-speaker array-at each location and -both of these-arrangements are relatively costly in that, full frequency range yloudspeakers are expensive and the multispeakers arrays are appreciably more costly and, of course, there is *always the problem of providing suitable'enclosuresor baflles forV the .speakers or speaker systems or arrays and where good low frequency vresponse is desired from both speaker locations this necessitates relatively-large speaker enclo- 2,904,632 Patented Sept. 15, 1959 ice 'termine the point -from which low frequency sound waves emanate, whereas middle and high frequency sound waves are highly directive and a listener'may immediately differentiate between the points from which middle 'and high frequency lsound waves mayv be emanating. yAs

a result of this fact, it has been found possible'to provide a perfectly suitable stereophonic sound propagation sys- Vtem in which the low rfrequency sound waves emanate from -only one point, while the middle and high "'equency -sound waves emanate from one or more points spaced from the low frequency loudspeaker and it has beenA found that this provides highly satisfactory stereophonic sound propagation and'at the same time, permits a material reductio'ninr size of the installation, particularly the loudspeaker enclosures and consequently there is a material reduction in cost.

It is accordingly an object of the invention tov provide a stereophonic sound propagation -system utilizing any suitable ysource of program material and which maybe designed to operate `satisfactorily in substantially vany room or other desired-location.

A further object of the invention is the provision of astereophonicv soundpropagation system having full frequency range-capabilities but utilizing only'two loudspeakers disposed in spaced relationship.

A still'further object of theinvention is the provision of yastereophonic sound propagation system utilizing lone full frequency range loudspeaker having two separate voice-coils with one voice coil serving to reproduce the `full frequency loutput of one program material-source and the other voice coil reproducing onlythe low frequency output of a second program material source va second loudspeaker reproducing only the middle and lhigh 'frequency output of the second program rmaterial Another-object of the invention is the provision of a stereoph'onic sound .propagation system utilizing a low frequency `range loudspeaker having two separate voice coils with one voice coil vconnected to one lsourcev of program material and the other voice coil connected .to the other source of program-material, `both of these connections being through low-pass rfilters to limit-the input to both voice coils to the lower frequencies and vamidd'le and .high frequency range loudspeaker disposed on'each side of the low frequency speaker, one vof the highfi'equency speakers being connected to one program material source through a high-pass lter and the other high frequency speaker being connected to the second program material source through a high-pass filter.

A further object of the invention is the provision -of a'stereophonic sound propagation system utilizing a full frequency range loudspeaker having two separate voice coils with one voice coil connected to the output-of one program material source and the other voice coil lconnected to the output o-f a second program sourceto reproduce the full frequency output of both program-material sources, a middle and high frequency range loudspeaker connected to the output of one program material source vthrough a high-pass filter and a second middle and high 'frequency range loudspeaker connected to the second program material source through a high-pass filter 4with the two high frequencies speakers reproducing only the middle and high frequency outputs of the two program material sources.

A still further object of the invention is the provision of a stereophonic sound'propagation system utilizinga 'loudspeakerhaving two separate voice coils, one voice coil lbeingconnected lto one program material Isource and the other voicecoil being connected to a second program material source and'at least one middle and high frequen- 'cy 'range loudspeaker -connected through -a high-pass lter to the output of either of 'theprogram material sources.

Another object of the invention is the provision of a stereophonic sound propagation system utilizing a plurality of loudspeakers disposed in spaced relation and in which a volume level control isl provided for each loudspeaker in order -to provide a proper balance between the outputs of the various speakers.

Further objects and advantages of the invention will be apparent from the following description taken in conjunction with the accompanying drawing wherein:

Fig. 1 is a diagrammatic view showing a stereophonic sound propagation system constructed in accordance with this invention and utilizing one full frequency range loudspeaker having two separate voice coils and one middle and high frequency range loudspeaker;

Fig. 2 a diagrammatic view showing a further form of the stereophonic sound propagation system of this invention and utilizing a low frequency range loudspeaker with two separate voice coils and two middle and high frequency range loudspeakers; and

Fig. 3 a view similar to Fig. 2, but showing a further modified form of 4the invention utilizing a full frequency range loudspeaker having two separate voice coils and two middle and high frequency range loudspeakers.

With continued reference to the drawing and particularly Fig. l, there is shown a stereophonic sound propagation system constructed in accordance with this invention and which may well comprise two sources of program material indicated in the drawing as amplifier A and amplifier B. While these sources are indicated as audio amplifiers, obviously the same may be any other suitable source of program material, such as AM and FM radio receivers. It is, of course, assumed that the audio output from the two sources of program material is in accordance with standard stereophonic sound recording principles.

The system shown in Fig. 1 also incorporates a full frequency range loudspeaker which may be of the direct radiator cone type or any other suitable type of loudspeaker having a wide range frequency response, but it is imperative that this loudspeaker 10 be provided with two separate voice coils 11 and 12. It has been found that the use of two separate voice coils provides superior performance in that, there is no possibility of coupling or interaction between the two amplifiers or other program sources connected thereto which conceivably could cause instability and distortion.

Voice coil 11 is connected through suitable conductors 13 with the amplifier A or other source of program material and a volume ylevel control 14 is provided in order to limit the input to the voice coil 11 from the amplifier A. Connected in this manner, the loudspeaker 10 will reproduce the full frequency output of the amplifier A and it is, of course, understood that by full frequency output is meant the full range of frequencies which the particular equipment is capable of providing `and reproducing.

The second voice coil 12 is connected Ithrough suitable conductors 15 with a low-pass filter 16 which in turn is connected through suitable conductors 17 with the output of amplifier B. It will, therefore, be seen that in addition to reproducing the full frequency output of amplifier A, Kloudspeaker 10 will also serve to reproduce only the low frequency output of amplifier B.

A middle and high frequency range loudspeaker 18 is provided with a voice coil 19 which is connected through suitable conductors 20 to a high-pass filter 21 which in turn is connected through suitable conductors 22 to the output of amplifier B. Provided in the connection between voice coil 19 and high-pass filter 21 is a volume level control 23. While the loudspeaker 18 has been referred to as a middle and high frequency range loudspeaker, it is, of course, understood that this can constitute a single loudspeaker or may be a plurality of speakers in which one is designed to reproduce the middle frequencies While the other is designed to reproduce only the high frequencies. However, a single speaker will normally provide satisfactory reproduction of both the middle and high frequency output.

In operation of the system shown in Fig. 1, it is, of course, understood that the loudspeakers 10 and 18 will be mounted in suitable speaker enclosures or bafiies and that they will be located at appropriate distances apart in the particular room where utilized in order to provide proper distribution of the sound emanating therefrom. Since all of the low frequency output from both amplifiers A and B is reproduced by the loudspeaker 10, no directional characteristics of such low frequencies will be evident to the listener, but since this loudspeaker 10 reproduces middle and high frequency output of amplifier A it is important that loudspeaker 10 be located in such a position that the middle and high frequencies will be directed yto the proper point in the listening area for maximum listening enjoyment. It is to be noted that middle and high frequency sound waves are highly directive and consequently placement of both of the speakers with due regard for the proper distribution of such middle and high frequency sound waves is important.

Since the loudspeaker 18 reproduces only the middle and high frequency output of amplifier B, this loudspeaker will, of course, be located in such a manner as to direct the sound emanating therefrom to an appropriate point in the listening area and since the loudspeakers 10 and 18 are located at spaced points, a stereophonic eect will result. The volume level controls 14 and 23 are provided in order to permit adjustment of the output from the two amplifiers to the two loudspeakers in order to balance the sound emanating therefrom whereby substantially true and life-like sound reproductions will result.

It will thus be seen that by the above described form of the invention there has been provided a relatively simple stereophonic sound propagation system utilizing a minimum number of loudspeakers and at the same time providing for proper sound propagation and for proper balance of the output level of the two loudspeakers.

A modified form of the invention is shown in Fig. 2 which may well comprise two sources of program material, such as amplifier A and amplifier B, and there is also provided a. loudspeaker 24 which has low frequency range response, having separate voice coils 25 and 26. Alternatively, its response may be restricted to low frequencies. Unless it is so restricted, voice coil 25 iS connected to a low-pass filter 27 which in turn is connected through suitable conductors 28 to the output of tamplifier A. Voice coil 26 is connected to a low-pass filter 29 which in turn is connected through suitable conductors 30 to the output of amplifier B. If the loudspeaker range is restricted to low frequencies, the low-pass filters are not required to be so effectual and may even be omitted in some cases'.

A middle and high frequency range loudspeaker 31 is provided with a voice coil 32 which is connected to a high-pass filter 33 which in turn is connected through suitable conductors 34 to the output of amplifier A between such amplifier and the low-pass filter 27. Connected between the high-pass filter 33 and voice coil 32 is a volume level control 35. Consequently, it will be seen that loudspeaker 31 operates to reproduce only the middle and high `frequency output of amplifier A.

Loudspeaker 31 is disposed at one side of the low frequency loudspeaker 24 in spaced relation thereto and disposed on the opposite side in spaced relation to the low frequency speaker 24 is a second middle and high frequency range loudspeaker 36 having a voice coil 37 connected to a high-pass` filter 38 which in turn is connected through suitable conductors 39 tothe output of amplifier B between the low-pass filter 29 and the amplifier B. Connected between the high-pass filter 38 and Vascii-,613:2

5 voice coil 37 isa volume' level control 40. It will thus be seen 'that loudspeaker- 36 operates to reproduce only the middle and high frequency output of amplifier B.

In the operation of the stereophonic sound propagation system shown in Fig. 2 and described above, the low frequency loudspeaker 24 reproduces the low frequency output from both amplifier A and amplifier B and since such low frequency output is non-directional as explained above, loudspeaker 24 may be positioned at any desired location in the room or other listening location. The loudspeakers 31 and 36, however, must be positioned in such a manner that the middle andhigh frequency sound waves emanating therefrom will be directed to proper points in the listening area, since such sound waves are highly directive and the listening audience will immediately sense the direction or point from which such sound waves emanate. The system shown in Fig. 2 is primarily designed to be utilized in relatively large listening areas since the loudspeaker Z4 will operate to fll in the center 'of the listening area with sound, whereas the system shown in Fig. l would, in all probability, operate more satisfactorily in a smaller listening area. Obviously, the relative output of the two loudspeakers 31 and 36 'may be adjusted by the volume level controls 35 and 40 and where properly placed in a listening area, this system will operate to provide true stereophonic sound propagation.

The further modified form o'f the invention shown in Fig. 3 is also primarily designed to be utilizedl in larger listening areas and in this system as in common with the other systems described above, there may be provided two sources of program material, such as amplifiers A land B. `In this system a centrally located full frequency rreproduce the full frequency output of both ampliers A and B.

A middle and high frequency range loudspeaker 46is provided with a voice coil 47 which is connected to a high-pass filter 48 which is connected through suitable conductors 49 tothe output of amplifier A. Thus it will lbe seen that the speaker`46 operates only the middle and -high frequency output from amplier A. A volume level control 50 may be provided in the connection'between the voice coil 47 and the high-pass filter 48 in'o'rder to control the output of speaker 46.

A second middle and high frequency range'loudspeaker 51 is provided with a voice coil 52 connected to a'highpass filter 53 which in turn is connected through suitable conductors 54 to the output of amplifier B. A volume level control 5S may be provided in the connection between the voice coil 52 and the high-pass filter 53 in Iorder to control the output of speaker 5 1. Consequently, it will be seen that speaker 51 operates -toreproduce `only the middle and vhigh frequency output of amplifier A's stated above, the system shown in Fig. 3 is well suited to use in relatively large listening areas in that,

`the full range loudspeaker 41 operates to reproduce the vfull frequency output of both ampliers and consequently adequately fills in the center portion of the listening area. The stereophonic effect is provided by the two middle and high frequency range loudspeakers disposed on opposite sides of the speaker 41 and this system occupies a relatively small space, since it is only necessary to provide a relatively large enclosure for the full range speaker 41, whereas the other speakers 46 and 51 may be disposed in relatively small enclosures which may be conveniently located at any desired point. Once again, in this system the provision of two separate voice coils 'on the central common speaker 41 operates to completely isolate the amplifiers A and B thereby y'eliminating any Vv:possibility `of 'coupling or interaction which 'might :cause instability |and distortion. The output from -speaker`s46 and 5-1 may be regulated by the volume level controls 50 and 55 in order to properly balance the sound output for the particular listening location in which the system .is vinstalled. The above described systems all utilize at least one loudspeaker having separate voice coils and various combinations of other middle andr 'high frequencyrange loudspeakers may be utilized to provide the stereophonic effect and the proper sound distribution to the listening area. This arrangement eliminates the necessity of providing exteremely large loudspeaker enclosures which iS Vnecessary Yin a `system utilizing a ,plurality of full range loudspeakers or loudspeakers arrays and consequently, installation problems and furniture arrangementsv in flis- Atening areas, [particularly in the home, are materially `reduced.

vA further advantagel of the double voice coil feature 'described above vis the substantially completesuppression ofi-hum caused by turntable motor vibrations. With the use lof two-element phonograph pickups hum cau-sed by motor vibrations may beobjection'able and connection of the two output channels to the ltwo voice coils inthe proper phase relationship serves to balance out-the lhum 4output resulting in signals having minimum hum content.

vIt will be obvious to those skilled in the art'that various changes maybe made in the invention without vdeparting from the spirit and scope thereof and therefore the `invention is not limited by that which is shown in the drawing and described in the specication', but yonly as indicated fin the appended claims.

What is claimed is: 1. A stereophonic so'und propagationfsystem'I compris'- ing two sources of program material, a full yfrequency 'only the low frequency output of said second source and a :middle and high frequency range loudspeaker-adapted to be disposed in spaced relation `on one side of fsaid first speaker, said middle and high frequency speaker being yconnected to said second :source 'through 'a high- Vpass lter to reproduce only the middle and high fre- "quency loutput of said second source.

`2. Asystem as defined in claim l in which a volume level control-is provided in the connection to' said yone voice coil of said first speaker and a second volume level control is provided between said high-pass vfilter and said -second speaker.

3. A stereophonic sound propagation system comprising two sources of program material, a full frequency vrange loudspeaker having two vseparate voice coils, 'one voice coil being rconnected to the first source-for reproducing substantially the full frequency output of said first-source, the `other voice coil being connected 'to the second source through a filter for reproducing only the lowfrequency output of said second source anda -second loudspeaker disposed in spaced relation'to one Vside of said 'first speaker, said second speaker being connected to said second source through a filter to reproduce only the Amiddle and high frequency output of said second source.

4. A stereophonic sound Ypropagation system comprising two sources of .program material, a loudspeaker having two separate voice coils, one voice coil being connected to the first source for .reproducing the output of said first source, the other voice coil being connected to the second source through a filter `for reproducing only the vlow frequency output of said second source fand arsecond loudspeaker disposed in spaced 'relation to 'one side of saidrst speaker, said second speaker' lbeing "connected to 'saidsecond ysource through a flter yto -i'eproduce only the middle and high frequency output of said second source.

5. A stereophonic sound propagation system comprising two sources of program material, a low frequency range loudspeaker having two separate voice coils, one voice coil being connected to the first source through a low-pass filter to reproduce only the low frequency output of said first source, the other voice coil being connected to the second source through a second low-pass filter to reproduce only the low frequency output of said second source, a first middle and high frequency range loudspeaker adapted to be disposed on one side of said first speaker, said middle and high frequency speaker being connected through a high-pass filter to said first source between said first low-pass filter and said first source to reproduce only the middle and high frequency output of said first source and a second middle and high frequency range loudspeaker disposed in spaced relation to said first, middle, and high frequency range, said second middle and high frequency speaker being connected through a second high-pass filter to said second source between said second low-pass lter and said second source to reproduce only the middle and high frequency output of said second source.

6. A system as defined in claim in which a volume level control is provided in the connection between each high-pass filter and each middle and high frequency range speaker.

7. A stereophonic sound propagation system comprising two sources `of program material, a low frequency range loudspeaker having two separate voice coils, one voice coil being connected to the first source through a filter to reproduce only the low frequency output of said first source, the other Voice coil being connected to the second source through a second lter to reproduce only the low frequency output of said second source, a middle and high frequency range loudspeaker adapted to be disposed in spaced relation to said low frequency speaker on one side, said middle and high frequency speaker being connected through a filter to said first source between said first filter and said first source to reproduce only the middle and high frequency output of said first source and a second middle and high frequency range loudspeaker disposed in spaced relation to said low frequency speaker on the opposite side, said second middle and high frequency speaker being connected through a filter to said second source between said second filter and said second source to reproduce only the middle and high frequency output of said second source.

8. A stereophonic sound propagation system comprising two sources of program material, a loudspeaker having two separate voice coils, one voice coil being connected to the first source through a filter to reproduce only the low frequency output of said first source, the other voice coil being connected to the second source through a second filter to reproduce only the low frequency output of said second source, a second loudspeaker disposed in spaced relation to said first speaker on one side, said second speaker being connected through a filter to said first source between said first filter and said first source to reproduce only the middle and high frequency output of said first source and a third speaker disposed in spaced relation to said first speaker on the opposite side, said third speaker being connected through a filter to said second source between said second filter and said second source to reproduce only the middle and high frequency output of said second source.

9. A stereophonic sound propagation system comprising two sources of program material, a full frequency range loudspeaker having two separate voice coils, one voice coil being connected to the first source for reproducing substantially the full frequency output of said first source, the other voice coil being connected to the second source for reproducing substantially the full frequency output of said second source, a middle and high frequency range loudspeaker disposed in spaced relation to said full range speaker on one side, said middle and high frequency speaker being connected to a high-pass filter to said first source to reproduce only the middle and high frequency output of said source and a second middle and high frequency range loudspeaker disposed in spaced relation to said full range speaker on the opposite side, said second middle and high frequency speaker being connected through a second high-pass filter to said second source to reproduce only the middle and high frequency output of said second source.

l0. A system as defined in clairn 9 in which a volume level control is provided in the connection between each high-pass filter and each middle and high frequency range speaker.

l1. A stereophonic sound propagation system comprising two sources of program material, a full frequency range loudspeaker having two separate voice coils, one voice coil being connected to the first source for reproducing substantially the full frequency output of said first source, the other voice coil being connected to the second source for reproducing substantially the full fre quency output of said second source, a middle and high frequency range loudspeaker adapted to be disposed in spaced relation to said full range speaker on one side, said middle and high frequency speaker being connected through a filter to said first source to reproduce only the middle and high frequency output of said first source and a second middle and high frequency range loudspeaker adapted to be disposed in spaced relation to said full range speaker on the opposite side, said second middle and high frequency speaker being connected through a second filter to said second source to reproduce only the middle and high frequency output of said second source.v

l2. A stereophonic sound propagation system comprising two sources of program material, a loudspeaker having two separate voice coils, one voice coil being connected to the first source, the other voice coil being connected to the second source, a second loudspeaker disposed in spaced relation to said first speaker on one side, said second speaker being connected through a filter to said first source to reproduce only the middle and high frequency output of said first source and a third loudspeaker disposed in spaced relation to said first speaker on the opposite side, said third speaker being connected through a second filter to said second source to reproduce only the middle and high frequency output of said second source.

13. A stereophonic sound propagation system comprising two sources of program material, a loudspeaker having two separate voice coils, one voice coil being connected to the rst source, the other Voice coil being connected to the second source, a second loudspeaker adapted to be disposed in spaced relation to said first speaker on one side, said second speaker being connected to said first source, and a third loudspeaker adapted to be disposed in spaced relation to said first speaker on the opposite side, said third speaker being connected to said second source.

14. A stereophonic sound propagation system comprising two sources of program material, a loudspeaker having two separate Voice coils, one Voice coil being connected to one source and the other Voice coil being connected to the second source and at least one middle and and high frequency range loudspeaker disposed in spaced relation to one side of said first named speaker, said middle and high frequency speaker being connected to either source through a high-pass filter to reproduce only the middle and high frequency output of said source.

l5. A system as defined in claim 14 in which a volume level control is provided between said high-pass filter and said middle and high frequency speaker.

16. A stereophonic sound propagation system comprising two sources of program material, a loudspeaker having IWQ Spatc voice coils, one voice coil being connected to one source and the other -voice coil being connected to the second source and at least one loudspeaker adapted to be disposed in spaced relation to one side of said first named speaker, said second speaker being connected to either source through a high-pass lter to reproduce only the middle and high frequency output of said source.

17. A stereophonic sound propagation system comprising two sources of program material, a loudspeaker having two separate voice coils, one Voice coil being connected to one source and the other Voice coil being connected to the second source and at least one loudspeaker disposed in spaced relation to one side of said rst named speaker, said second speaker being connected to either source.

18. A stereophonic sound propagation system comprising -two sources of program material, a loudspeaker having at least low frequency range response and having two separate voice coils, a middle and high frequency range loudspeaker adapted to be disposed in lateral spaced relationship to said first loudspeaker, one voice coil of said first loudspeaker being connected to one source, the other voice coil of said iirst loudspeaker and said second loudspeaker being connected to the other source and means for limiting the reproduction of middle and high frequency range output of said other source by said other voice coil of said iirst loudspeaker.

19. A stereophonic sound propagation system as delined in claim 18 in which the means for limiting the reproduction of middle and high frequency range output by said other voice coil comprises a low-pass filter connected between said other source and said other voice coil.

No references cited.

Non-Patent Citations
Reference
1 *None
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3076873 *Jun 25, 1959Feb 5, 1963Motorola IncAmplifier system
US3083264 *Dec 10, 1959Mar 26, 1963Bell Telephone Labor IncSum and difference stereophonic transmission with negative feedback
US3176072 *Apr 21, 1960Mar 30, 1965Muter CompanyStereophonic reproduction system
US3417203 *Apr 13, 1965Dec 17, 1968Dynaco IncTwo-channel stereo system with derived center channel
US3934086 *Aug 16, 1974Jan 20, 1976Sansui Electric Co., Ltd.Matrix four-channel decoding system
US4084474 *Feb 4, 1976Apr 18, 1978Donald James LeslieSelective high frequency compression device for speaker system
Classifications
U.S. Classification381/1
International ClassificationH04S3/00
Cooperative ClassificationH04S3/00
European ClassificationH04S3/00