CHAPTER 13 - Sources of Sound and Sound Waves

Abstract

This chapter discusses different sources of sound and sound waves. Sound is produced by a vibrating body acting as a source and this set up a longitudinal sound wave in the surrounding medium. Sounds have three major characteristics, namely, pitch, intensity, and quality. Frequencies above the upper limit of audibility are called ultrasonic or supersonic when they refer to mechanical vibrations of a source or of the medium transmitting the disturbance and which are thus of the same character as sound waves or vibrations. Sound waves consist of the longitudinal compressions and refractions of the medium through which the sound is passing, and it must be stressed that a material medium is required for the propagation of sound. The phenomenon of reflection, refraction, interference, and diffraction are all exhibited by sound waves. If two waves of nearly the same frequency are received together by the ear, beats are heard, which implies that the sound alternatively increases and decreases in intensity at a frequency, known as the beat frequency. When a system is stationary and does not progress with time, then, it is called as a stationary or standing wave system. The velocity of sound in a tube or pipe is different from that in free air.