Richardson's handbook of projection (1930)

968 HANDBOOK OF PROJECTION FOR air) will also be high. Between the lowest and the highest are thousands of possible variations. Get this fact clearly: The tone and quality of sound is entirely dependent upon the combinations of frequencies of the waves set into motion in the atmosphere by the vibrating element of the thing producing the sound. As the frequency (number of vibrations, or waves per second set up in the air by the thing producing the sound) increases, the pitch of the sound, as heard by the ear, increases, or is raised, and vice versa. I have put this in various forms of words, to the end that there be no misunderstanding of the matter. It is a basic principle, and must be clearly understood if one is to understand the action of sound recording and reproducing apparatus. As I have said, the sound waves traveling through the air cause an exceedingly thin metal plate or disc, called the "diaphragm" of the microphone to vibrate with a speed exactly equal to their own, which same is of course varying constantly with each change or modulation of sound, no matter how slight. I have no apologies to make for repetition in these matters. It is absolutely essential to an understanding of the action of sound recording and reproducing equipment that you have a clear understanding of them. In the type of microphone called the "Condenser Type," which is now universally used for recording, the diaphragm forms or is one plate of an air condenser. By "air condenser" it is meant that the plates (see "The Condenser," page 1017) are insulated from each other by air. The other plate is in the form of a flat metal disc of considerable thickness. The two are separated by from one to two thousandths (.001 to .002) of an