TAILIEUCHUNG - HVAC Systems Design Handbook part 20

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. | Source HVAC Systems Design Handbook Chapter 20 Engineering Fundamentals Part 5 Sound and Vibration Introduction 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. Definitions 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. . 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 . 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. 485 Downloaded from Digital Engineering Library @ McGraw-Hill Copyright 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Engineering Fundamentals Part 5 486 Chapter Twenty Figure Sound transmission. Methods of Specifying and Measuring Sound There are several ways of describing the characteristics of sound sound power sound pressure intensity loudness frequency speed and directivity. Sound power An acoustical source radiates energy in the form of sound. This acoustical power is expressed in watts. A watts exponential scale of sound power has been

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