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1954-55 Theatre Catalog, 12th Edition, Page 278 (242)

1954-55 Theatre Catalog, 12th Edition
1954-55 Theatre Catalog
1954-55 Theatre Catalog, 12th Edition, Page 278
Page 278

1954-55 Theatre Catalog, 12th Edition, Page 278

of sound having direction and depth in the area between the loudspeakers.

It is very important to distinguish between these systems. A binaural transmission system actually duplicates in the listeners ears the sounds he would hear at the pickup point, and except that he cannot turn the dummy head, gives full normal directional sense in all directions. A stereophonic system produces an abnormal sound pattern at the listeners ears which his hearing sense interprets as indicating direction in the limited space between the loudspeakers. It has been aptly said that binaural systems transport the listener to the original scene, whereas the stereophonic sound system transports the sound source to the listener's room.

Elecfro-Aoousfic Sound Reproducing Systems

Outstanding differences and similarities of the various types of electroacoustic reproducing systems are summarized in the chart of Figure 1. The "Systemf names in column 1 conform to a uniform pattern and will be found in the literature, except ffmonophonic" which is used for convenience as the opposite of stereophonic. ftEquivalent Normal Experiencef refers to the everyday hearing experience that most closely parallels listening over the systems in question. The next four columns are obvious. The column "Direct Sound Reproduction of Single Source Pulse" is probably the most important, since it gives the basic differences between the

sound reproduced by the various systems. If a single sound pulse is produced by the source, this column gives the characteristic of the resulting direct sound pulses at the observer's ears. The direct sound is the initial sound transmitted directly from source to observer by the shortest path, and arriving before any reflected sound arrives. It has been found that the direct sound carries the information, making angular perception possible, and it will be referred to fr quently in what follows. Reverberant sound arrives from many angles and confuses the directional perception if too great in intensity. The "Remarks" column gives qualifying comments concerning the sound reproduction of each system. The reasoning behind these remarks is given in the body of the paper.


Binaural reproduction as used herein means ordinary two-ear listening since the reproducing system transmits a faithful copy of the original to the listeners ear.

Angular Localization

The properties of hearing which give the directional sense in binaural listening have been studied extensively. For pure tones angular localization is produced partially by phase differences at the two ears caused by the difference in distance from source to the ears, as the

FIGURE 1 is a chart summarizing the various types of electroacouslic reproducing sysloms.

source angle changes. The phase effect becomes ambiguous somewhat above 1000 cycles because at short wavelengths more than one angle results in the same phase difference. However, in the higher frequency region intensity differences produced by the diffraction or sound-shadow effects of the head and external ears become great enough to give angular localization.

The great majority of sounds are not pure tones, but complex. For complex sounds the equivalent effects are arrival time and quality difference. A complex wave pulse has an initial wavefront which arrives at the near ear a short time before it arrives at the far ear. It is this small time difference which is used by the hearing sense to determine small angular variations, particularly for sounds near the median plane (straight ahead). It is characteristic to turn toward a source to locate it with maximum precision, and for impulsive sounds such as speech or clicks, differences as small as 1 degree to 2 degrees can be perceived. These angles correspond to arrival-time differences of about 10 to 20 usec, and the maximum possible difference, for a source in line with the two ears, is only about 700 usec, The loudness differences at such small angles are negligible, and it must be assumed that the arrival-time differences give the localization clues. On the other hand, it is not possible for the mechanism of a single ear to distinguish such short time intervals; this fidecoding" of the arrival time differences must be accomplished by the brain.

Equivalent Number Direct sound normal of I reproduction of Type of svsicm experience Pickup channels Reproduccr Symbolic schematic single source pulse Remarks Monaural One car 1 Microphone 1 l Headphone um 1 Pulse to 1 car Only partial equivalence. as directional plugged got-Ia 03W: effects are not duplicated (9.- -oomvu Diofic Sound source 1 Microphone 1 2 Headphones 1 Pulse to each ear Only partial, as directional efTects of in median Q"- 0 time difference elevation not duplicated. No direcplanc only No quality differ- tional effect pf room reverberation cncc Qualitativer much superior to monaural Binaural Normal listen- 2 Microphones 2 2 Headphones 1 Pulse to each ear Directional and quality effects of normal ing, head in artificial g,--ri 0 to 0.6 mscc time listening in pit/cup roam duplicattl stationary hcad @nu difference throughout 360o sphere ;;,mm Normal qualin Na listening room effects nun differences Observer cannot turn to face virtual source "Monophonic" Sound coming 1 Microphone 1 l Loudspeaker 1 Pulse to each ear Both cars used-binaural listening to a ordinary through a g, 0 time differences single fixed sound source position loudspeaker hole in a @"""D-*4=s No quality diffcr- Composite of pickup and listening room wail ences acoustics Listening room reverberation has direclivity Represents widely spaced *cfl'ccts" loudspeakers Slercophonic None 2 or more micro- 2 or 2 or more 2 or more pulses to Depends on fusion of multiple pulses by phones more loudspeakers each car cars @: 24$ 010 30+mscc timc Directional and quality effects of normal \\\ / \ differences listening n'mululnl for a [build angular H-"t' Com cx quality area appearing as part oilirkm'ng room di crcnccs 360" simulation would require a large number of channels Composite of pickup and listening mom acousqu Rcverbcralion has partial directivin in pickup room, full dircctiviiy in isrcning room Observer can turn to face virtual source Time differences from both source and observer positions N n 1 Micro hone 2 or 2 or more 20r more pulse-(o Single source only . ' v o c P more loudspeakers Inch ear Many properties identical wnh iruc monophonic @u- 0 to 20+ mace stereo home system time difference: Time Ifl'crencea only from observer Small qualify position, and detrimental vow- co-vmu difference! Identical signal-reverberation pattern from each loudspeaker Identical ualily from each loudspeaker Many other bridged combination: possible 242 THEATRE CATALOG 1,5445
1954-55 Theatre Catalog, 12th Edition, Page 278