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1954-55 Theatre Catalog, 12th Edition, Page 284 (248)

1954-55 Theatre Catalog, 12th Edition
1954-55 Theatre Catalog
1954-55 Theatre Catalog, 12th Edition, Page 284
Page 284

1954-55 Theatre Catalog, 12th Edition, Page 284

Bridged LoudspeakerseIt is possible to bridge a center loudspeaker across the outside channels, which has the effect of reducing the apparent stage width. This would be useful if it were impossible to place the side loudspeakers as close together as desired. It would be subject to limitations of bridged systems already pointed out.


Placement * Microphone placement may be simple or complicated depending on the application. From what has been said, it will be evident that creating the stereophonic illusion is a compromise between favorable and unfavorable factors, and microphone placement and movement can be used to advantage in effecting this compromise. Since the illusion depends upon differences in intensity and arrival time at the microphones, and change in ratio of reverberant to direct sound, the microphones must be placed close enough to the sources to create these differences. This means that each microphone ticoversii only part of the stage and will be closer than fixed microphones placed for a single pickup. If pickup of action is necessary in a room Where ordinary

248' :

LEOPOLD STOKOWSKI and the author. right. operating controls at 1939 recording session.

reverberation times obtain, the necessity of close pickup is apt to accenturate depth effect, and require a small stage area. Then dimensions are multiplied if a larger reproducing stage is used, and the speed of movement on the pickup stage must be slowed by an appropriate factor. Conversely, if the action demands .a large stage, special microphone - handling techniques, such as those described by Grignon, will probably be necessary. A good combination is a dead stage in which a set of the size that will accommodate the action can be constructed with the proper combination of fiats to give a reflected sound content that will produce the desired depth illusion.

The motion picture industry is rapidly developing the art of microphone movement for stereophonic recording where action and movement of camera are all-important. For other stereophonic pickup, such as music, radio plays or sound reinforcement, fixed microphone positions aided by some mixed-in special pickups will usually suffice. The regular microphones are deployed in front of

the stage. If all action is at front stage, the outside microphones should be at the outside edges. However, to secure the illusion of action on a rectangular stage requires a greater stage width at the rear line than at the front, and some compromise must be made; so the side microphones are usually placed somewhat inside the edges. This is particularly true of a two-channel system where a compromise between "hole-inthe-center" sound and well spread sound must be effected. In this connection, a bridge center microphone is frequently used and does fill up the hole for center observing positions, However, it obtains this effect by adding sound to the side channels at advanced arrival time, thus aggravating the shift of the virtual source as the observer moves to the side of the auditorium.

After considerable experimentation the microphones for the Philadelphia Orchestra recordings demonstrated by the Bell System in 1940, were suspended 10 feet above the stage and five feet inside the front row of musicians. The orchestra width was about 40 feet and the outside microphones were 28 feet apart. For small stages with actors, good results were obtained with a 12 foot square stage in a very dead room using two microphones nine feet apart and five feet from the front of the stage. In a rather reverberant mediumsized room a stage 15 feet Wide and six feet deep, using three channels, with the microphones on six foot centers and four feet from the front line, proved satisfactory. In this case, note the shallow depth dictated by the reverberation in the room.

DirectivityeDirective microphones can frequently be used to advantage. Since to produce an angular illusion it is necessary to generate intensity differences in the channels, a study of the geometry will show that greater movement is required at the rear lof the pickup stage than at the front to produce a given angular impression. If the microphones are directive, greater intensity changes will occur as a source

POWER EQUIPMENT on stage of Pantages Theatre, Hollywood. during demonstration lune. 1940.

1954-55 Theatre Catalog, 12th Edition, Page 284