Richardson's handbook of projection (1930)

1074 HANDBOOK OF PROJECTION FOR they will sound like those you would expect to hear were pygmies about two feet tall talking. It will be entirely unnatural. This, we will be convinced by a moment of consideration, cannot possibly be through any fault of the receiver itself. What is coming from it is all there is. The receiver can send no more through with a horn attached than it does without the horn attached. That is plain common sense, yet if we, without changing anything else, attach the horn, we find the thin shrill sounds to instantly come forth writh full resonance, and apparently with enormous amplification. Naturally we wish to know why this is so. As nearly as I am able to put the thing into understandable words, this is what takes place. The receiver alone does transmit all the sound there is, but it is unable, unaided by a properly constructed horn of proper length, to connect to or deliver to the great body of air any but the higher sound wave frequencies. What the properly constructed horn of proper length does is to form a connecting link between the receiver and the outer air for those same high frequencies, plus the low frequencies. In other words it makes available to the air all the sound wave frequencies within range of the horns, which in motion picture practice run as low as sixty, or even somewhat lower. Please do not ask me why this is so. I don't know, and by that same token I am not at all certain the experts on such matters know either. We do know, however, that that is the fact. In constructing horns it has been found necessary to have the walls formed in an exactly calculated shape