US2846504A - Stereophonic sound transmission system - Google Patents

Description

Aug. 5, 1958 R. M. MIKULYAK 2,846,504

STEREOPHONIC SOUND TRANSMISSION SYSTEM Filed Nov. 19, 1956 SOUND SOURCES INVENRDR RM. M/KULYAK wmwzo- United States Patent sTEREoPHoNIc oUNn TRANSMISSION SYSTEM Robert M. Mikulyak, Stirling, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application November 19, 1956, Serial No. 623,133

6 Claims. (Cl. 179-1) This invention relates to stereophonic sound transmission systems.

The object of the invention is to provide a sound transmission system comprising stereophonic recording and reproduction whereby there is conveyed to the listener the impression that the intelligence is being communicated to him directly from the source.

In accordance with the invention, two directionally sensitive microphones are located at the front center of a sound originating area each with its axis of maximum sensitivity directed toward a difierent side of the area. The microphones are disposed substantially back to back.

A separate recording-reproducing channel is associated with each microphone. Two separate sound tracks may be recorded and later reproduced simultaneously through separate amplifier and loudspeaker means, or each microphone may be directly coupled to its associated power amplifier and loudspeakers. In any event, a single loudspeaker is individually connected to each reproducing channel and located at a side of the reproducing area corresponding to the position of its associated microphone in the recording area.

A particular feature of the invention resides in the use of intermediate speaker assemblies disposed in front of the sound reproducing area between the single side loudspeakers. Each of these assemblies consists of two loudspeakers one of which is fed from one channel and the other of which is fed from the other channel. Each loudspeaker is fed through attenuating means operative to reduce its output level by an amount corresponding to the reduction in the pickup of the microphone associated therewith as determined by the point on the directional sensitivity characteristic of the microphone corresponding to the lateral position of the loudspeaker in the sound reproducing area.

The nature of the invention and its distinguishing features and advantages will be more clearly understood from the following detailed description and the accompanying drawings in which:

Fig. 1 is a diagram of a two-channel stereophonic recording system showing the outline of the recording area, the relative location of the microphones and the directional sensitivity characteristic of each microphone at a particular frequency;

Fig. 2 is a diagram showing the volume level patterns of signals received by the microphones and transferred to the loudspeaker assemblies; and

Fig. 3 is a diagram of a two-channel stereophonic reproducing system showing the outline of the reproducing area, and the relative location of the speaker assemblies or groups to which signals received by the microphones are transferred in accordance with the volume level patterns shown in Fig. 2.

Referring now to the accompanying drawings sound pickups or microphones A and B are located at the front center of the sound producing area or recording stage 12, each with its axis of maximum sensitivity, 14 and 16 respectively, directed toward a different side of the sound area 12. In the embodiment shown in Fig. 1 the microphones are disposed substantially back to back, each with its axis of maximum directional sensitivity at a predetermined angle to the center line of the sound originating area, and each associated with a separate recording channel. The microphones are connected by separate transmission lines 18 and 22, and through amplifiers 24 and 26, to recorders 28 and 30, which cooperate with record media 32 and 34. With this arrangement the outputs of microphones A and B may be recorded on records 32 and 34 respectively. Any well-known method may be used to record the outputs of microphones A and B. Recorders 28 and 30 may comprise magnetic transducers and sound record media 32 and 34 may be standard motion picture film with a recording surface of magnetic oxide.

Curves AM and BM are the directional sensitivitycharacteristics of microphones A and B respectively at a particular frequency. Vector A 0 represents the maximum sensitivity of microphone A for the sound source at 1, while vector B 0 represents the maximum sensitivity of microphone B for the sound source at 1. Vectors A 0 and B 0 represent the maximum sensitivity of microphones A and B respectively for the sound source at 2, and vectors A 0 and B 0 represent the maximum sensitivity of microphones A and B respectively for the sound source at 3.

As shown in Fig. 3, loudspeaker SA is connected to the reproducing channel comprising the record medium 32, reproducer 38 and amplifier 40, and is located at a side of reproducing area or stage 42 corresponding to the position of its associated microphone A in the recording area 12. Loudspeaker SB is connected to the reproducing channel comprising the record medium 34, reproducer 44 and amplifier 46, and is located at a side of reproducing area or stage 42 corresponding to the position of its associated microphone B in the recording area 12.

There are two playback channels which correspond to the two recording channels, and the two sound tracks obtained during the stereophonic recording are played back simultaneously. However, instead of using only the side loudspeakers SA and SB as in a conventional binaural system, a multispeaker system is used. A plurality of reproducing assemblies are disposed between loudspeakers SA and SB. Each reproducing assembly comprises two loudspeakers, each connected through an attenuator to a different one of the two reproducing channels. The loudspeakers SA, SA2, SA4, SAG, SB, SE2, SE4 and SE6 will have volume levels associated with their locations as determined by the curves shown in Fig. 2.

The volume level patterns shown in Fig. 2 are established by plotting the directional sensitivity of each microphone (over the range from maximum to zero sensitivity for each sound source) against uniformly increased abscissas, the maximum one of which is equal to the length of the reproducing area or wall along which the loudspeakers are disposed. The volume level of each loudspeaker in the sound reproducing area will correspond to the volume level of sound received by its associated microphone as determined by the point on the directional sensitivity characteristic of said microphone corresponding to the lateral position of the loudspeaker in the reproducing area.

Signals from the three sources 1, 2 and 3 are received by microphones A and B at the volume levels indicated by A1, A2, A3, B1, B2 and B3. These signals are reproduced by the speaker reproducing assemblies in accordance with the volume level patterns shown in Fig. 2 wherein the sums of the levels provided by both channels are shown by dotted curves.

Since the lower frequencies have very little efiect on used in the assemblies disposed between the side loudspeakers.

' Moreover, by using two separate loudspeakers fat each intermediate position, the signals from the two channels are mixed acoustically and any phase diflerence in the signals from the two sound tracks is less likely to cause distortion than would be'the case if they were mixed electronically and reproduced through a single loudspeaker. with acoustical mixing may be lessened by turning for directing the loudspeakers of an intermediate speaker assembly at a slight angle away from each other. The impression of direct communication may be further enhanced by interchanging the positions of the speakers in the intermediate assemblies. For example, speaker S136 would occupy the position occupied by speaker A2 in Fig. 3, and vice versa, and each of the speakers would be directed at a slight angle away from the other with speaker SB6 turned toward speaker SA and speaker 8A2 turned toward speaker SB.

As noted heretofore sound tracks need not be recorded and microphone 28 may be coupled directly to amplifier 40 and loudspeakers SA, SA2, SA4 and SA6, and microphone 30 may be coupled directly to amplifier 46 and loudspeakers SB, S132, SB4 and SE6.

' It is to be understood that the above-described arrangements are illustrative of the application of the principles of the invention. Other arrangements may be devised by those skilled in the art without departing from the spirit and scope of the invention.

What is claimed is: V

1. A stereophonic sound transmission system'cornp-rising a pair of directionally sensitivemicrophones disposed adjacent each other substantially back to back at the front center of a sound originating area each with its axis of maximum directional sensitivity directed toward a different side of said sound originating area, a separate reproducing channel associated with each of said microphones, a sound reproducing area, a loudspeaker connected to each of said reproducing channels andlocated at a side of said sound reproducing area corresponding to the location ofits associated microphone in said sound originating area, a source of sound in said sound originating area, the volume level of each of said side loudspeakers corresponding to the maximum volume level of said sound received by its associated microphone, as determined by the directional sensitivity characteristics of said microphones, a plurality of reproducing assemblies disposed between said side loudspeakers, each of said reproducing assemblies comprising two loudspeakers each 2. A stereophonic sound transmission system comprising a sound originating area, a pair of directionally sensitive microphones disposed adjacent each other substantially back to back at the front center of said sound originating area each with its axis of maximum directional sensitivity at a predetermined angle to the center line of said sound originating area, a separate reproduc- Also, the chance of phase difference distortion ing channel associated with each of said microphones, a sound reproducing area, a loudspeaker connected to each of said reproducing channels and located at a side. of said sound reproducing area corresponding to the location of its associated microphone in said sound originating area, a source of sound in said sound originating area, the volume level of each of said side loudspeakers corresponding to the maximum volume level of said sound received by its associated microphone, as determined by the directional sensitivity characteristics of said micro phones, a plurality of reproducing assemblies disposed between said side loudspeakers, each of said reproducing assemblies comprising two loudspeakers each connected through attenuating means to a .diiferent one of said reproducing channels, each of said attenuating means being 4. In a stereophonic sound translating system a sound originating area, a source of sound in said area, a pair 7 of directionally sensitive microphones disposed adjacent each other substantially back to backat'the front center of said sound originating area each with its axis of maximum directional sensitivity at a predetermined angle to the center line of said sound originating area, a separate recording channel connectingeach microphone with an individual recording device for recording two separate.

phone associated with therecord to be reproduced, the

volume level of each of said side loudspeakers corresponding to the maximum volume level ofsaid sound received by the microphone associated therewith, as determined by the directional sensitivity characteristics of said micro phones, a plurality of reproducing assemblies disposed between said side loudspeakers,, each of said reproducing assemblies comprising two loudspeakers eachconnected through attenuating means to a different one of said re-.

. producing channels, each of said attenuating means being operative to reduce the output level of its associated loudspeaker by an amount corresponding to the reduction in,

the pickup of the microphone associated therewith as determined by the point on.the directional sensitivity characteristic of said microphone corresponding to the lateral position of said loudspeakerin said sound -reproducing area. g

5. A sound system in accordance with-claim 4 Wherein the signals received by said microphones are recorded magnetically.

6. A sound system in accordance withclaim 4 wherein the loudspeakers in eachof said reproducing assemblies are angularly disposed, each being turned away from the other. r

No references. cited.

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