TABLE OF CONTENTS The HVAC designer cannot neglect consideration of the sound and vibration generated by HVAC equipment. This chapter briefly discusses the fundamentals of sound and vibration control. References for further study are cited at the end of the chapter.
Sound is a form of energy, detected as a variation in pressure and stress in an elastic or viscous medium. The traditional concept is that sound is generated by a source and is transmitted through a path to a receiver (Fig. 20.1). Diminishment of the sound during transmission is called attenuation. The receiver is usually a human ear or a microphone. The audible range of hearing for humans is roughly between 20 Hertz (Hz) and 20,000 Hz. Many animals have a wider range. Lower frequencies can sometimes be felt.
Vibration is a form of energy, detected as cyclic movement in a machine or structure. Sound and vibration are mutually convertible, and many transmission problems and solutions depend on this fact.
Noise is unwanted sound. One person s sound may be another person s noise, e.g., heavy-metal rock music. In general, however, noise is random sound. White noise, used for masking unwanted sound, is random sound in the speech interference range.
There are several ways of describing the characteristics of sound: sound power, sound pressure, intensity, loudness, frequency, speed, and directivity.
An acoustical source radiates energy in the form of sound. This acoustical power is expressed...
