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SPEAKERS 595
A diaphragm that has become loosened, bent or warped, or that has lost its elasticity, will seriously damage sound quality. It may rattle, or create raspy sound at some one frequency or at high volume. It can seldom be repaired, and in most cases is replaced. Trouble of this kind can usually be heard at once. Where there are several speakers, however, it may be necessary to listen with an ear close to each, until the faulty one is discovered. If two speaker units are mounted on a double-throated horn one must be turned off to trace trouble of this nature.
Transmission Line Troubles
(15) The transmission line can cause bad sound through improper impedance match, as when such tap switches as those shown in Figure 143 are misadjusted. Impedance mis-match will also follow if speakers are replaced carelessly with others of a different make or type. Such replacements may call for changing the output transformer of the amplifier, or a satisfactory adjustment may be made by choosing a suitable speech transformer to be mounted on the speakers themselves, but it is not possible to wire speakers to an amplifier promiscuously and expect satisfactory results.
Stage cables leading to the speakers may prove a serious source of trouble if the stage is used for vaudeville or other entertainment, and the cables subjected to being stepped on. Sooner or later they will resent such treatment and stop a show. Wherever the stage is in use all speaker supply cables should be run overhead.
Pin connectors are sometimes used when speakers have to be moved offstage to make room for a show. These also are a source of possible trouble. Looping the supply cables overhead makes their use unnecessary.
Poling Speakers
(16) Whenever more than one speaker is used it is vitally necessary that all diaphragms move inward and outward in synchronism. If the diaphragms move in opposite directions the sound waves they create will be 180 degrees out of phase and most of the volume will be