International projectionist (Jan-Dec 1956)

Nl NATIONAL P 'mm' 0k TIONIS VOLUME 31 FEBRUARY 1956 NUMBER 2 ACOUSTICS in PROJECTION By MARK STEVENS DON'T TRUST that monitor speaker! The sound heard in the projection room only roughly resembles the sound heard by the audience in the auditorium. The monitor may be perfect, as such speakers go, — but that makes no difference! The purpose of the monitor is to keep the projectionist informed as to whether or not the sound system is operative. Only the most serious defects of sound reproduction can be heard in the monitor above the whir of the projectors. The monitor, therefore, must never be accepted as an indicator of 'sound quality. Earphones are better for this purpose, as they permit the lower frequencies of sound to be heard and they shut out the noise of the projectors. But even earphones can do no more than reproduce the output of the system. The audience, listening to the stage speakers, hears a more or less modified reproduction of the amplified "signal." Yes, almost anything may happen to the sound in the auditorium. If the phasing and acoustic balance of the high and low-frequency speakers are incorrect, the quality of the sound is very seriously affected. Echoes may garble the dialogue, and reverberation may produce distortion. And none of New equipment, such as a magnetic stereophonic system, will greatly improve a theatre's sound reproduction, but optimum results are obtained only with good acoustical conditions. these untoward events is reported by the projection-room monitor! The ever-changing size of the audience and the noise created by patron movements, laughter, whispering, etc., are tremendously important factors affecting sound reproduction. Such volume must be changed from time to time to compensate for these factors. But how is the projectionist to know if the house is quiet or noisy? A nearly soundproof wall separates him from the people he is trying to please! Regulating Volume This is where an auditorium sound observer steps into the picture. By "sound observer" we mean an intelligent listener who has average hearing and a sense of dramatic values. We don't mean the hard-of-hearing patron who complains every time he misses a word, and we certainly don't mean the choleric usher whose nerves fray under the impact of .high-level music or sound effects. The projectionist must have absolute confidence in the judgment and diligence of the fellow who listens to the sound and signals for desired changes in the volume. One buzz for more volume and two for less are the usual signals. If the projectionist really trusts his man Friday in the auditorium, he'll not complain even if the buzzer rings several times during a show. Perhaps noisy children have quieted down, requiring less volume. Or a large party of late-show patrons may have come in, calling for more volume — and less after they have become settled in their seats. Volume changes should not exceed one point on the fader or potentiometer scale. If the change is not great enough to satisfy the sound observer, he will ring again — a procedure which should be discussed and thoroughly understood by both parties. A buzzer that rings two or three times in a row should not be taken to indicate impatience. Let's take a look at the stage speakers and auditorium to find out what acoustic conditions may affect the sound reproduction adversely. We shall have to assume that the sound heads and amplifiers are in good working order, and that the sound current impressed upon the voice coils of the speakers is free from distortion. Modern motion-picture sound apparatus is capable of giving excellent results. Why, then, is the sound so unsatisfactory in a large number of theatres having sound systems of the best quality? Reproduction is sometimes "tinny," sometimes "boomy," INTERNATIONAL PROJECTIONIST FEBRUARY 1956