CHAPTER 16 - Measurement of Sound Intensity. Recording and Reproduction. The Doppler Effect

Abstract

This chapter reviews various measurement techniques for sound intensity, recording and reproduction, and the Doppler effect. The intensity of a sound wave at any point is defined as the energy per second that is carried across unit area normal to the direction of travel of the wave at that point. The loudness of two sounds of different frequency may appear to be the same to an observer of normal hearing even though the intensities differ. A microphone is an electroacoustic transducer that is required for the purpose of recording, as well as for the immediate transmission of sound by line or radio transmission. The process of reconverting currents of audio frequencies into sound waves requires a device, such as a telephone earpiece or loudspeaker. The Doppler effect concerns the apparent change in pitch of a source of sound either because of its own motion or that of the observer, that is, because of any relative motion between source and observer. The persistence of sound in an enclosed space because of the reflection is called reverberation and the reverberation time is measured as the interval of time for the sound to fall in intensity by 60 db from its initial value after the source of sound is silenced.