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THE NATURE OF SOUND
Professor A. W. Nye*
It is our purpose in these introductory lectures to describe and discuss the fundamental principles and phenomena of sound, particularly those which enter importantly into the problems of recording and reproducing, so that succeeding lecturers may present to you their use and application to the work of the studio.
We are concerned, first of all, with the origin and nature of sound and how it travels from place to place ; after that with its reflection, refraction, diffraction, absorption, interference; with its effects on diaphragms, human ears, and other things which it strikes; with methods of making the sound create a similitude of itself in the form of a varying electric current or a varying light beam ; with the reversal of this action into sound again; with the considerations of what are the causes of "quality" in tones; and with many other phenomena.
In order to get a mental picture of the way in which sound originates and travels, we might imagine a very long horizontal pipe having a light, snugly fitting plunger at one end and a great many pressure gages attached along the pipe. Suppose that these gages are made so as to indicate pressures either above or below normal atmospheric pressure.
Then if we cause the plunger to be moved quickly forward, then backward an equal amount, and finally returned to its original position, and if we watch the pressure gages during this action, we will see gage 1 first show an increased pressure, then 2, then 3, and finally the last gage. But we will also notice that by the time the increased pressure has reached the gages part way along the pipe, the readings of earlier gages have decreased and some have .even reversed their readings and show a pressure less than normal, due to the decrease of pressure caused by the backward motion of the plunger; so that at
*Head of Physics Department, University of Southern California
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