tailieunhanh - Handbook of Machine Design P52

Noise is unwanted audible sound. Sound is essentially a fluctuating pressure disturbance that may act locally or propagate away from its source. Extremely intense sound can cause structural damage or equipment malfunctions, but usually its effect on humans is the primary concern. | CHAPTER 45_ NOISE AND ITS CONTROL David A. Towers RE. Senior Consultant Harris Miller Miller Hanson Inc. Lexington Massachusetts Erich K. Bender . Divisional Vice President Paul J. Remington . Principal Engineer Eric E. Ungar . . Chief Consulting Engineer Bolt Beranek and Newman Inc. Cambridge Massachusetts INTRODUCTION NOISE MEASUREMENT AND ANALYSIS NOISE EFFECTS AND STANDARDS NOISE CONTROL REFERENCES INTRODUCTION Noise is unwanted audible sound. Sound is essentially a fluctuating pressure disturbance that may act locally or propagate away from its source. Extremely intense sound can cause structural damage or equipment malfunctions but usually its effect on humans is the primary concern. Noise can annoy people can lead to interference with speech communication can interfere with the performance of mental and delicate manual tasks and if it is intense enough can cause discomfort pain and temporary or permanent hearing damage. Fortunately many aspects of noise and its effects are well enough understood to permit their consideration in the design process. Sound can occur and propagate in any gas liquid or solid medium but sound in air is usually of primary interest. Sound may be produced by any phenomenon that can lead to fluctuating pressure disturbances. These phenomena include 1 rapid expansion of gases or injection of fluid volumes such as from explosions and engine exhausts 2 repetitive interruptions or modulation of airflows such as by siren disks or fluctuating valves 3 turbulence as present in fluid streams emerging from nozzles or duct grillages and 4 vibrating solid surfaces. In many practical situa- STANDARD HANDBOOK OF MACHINE DESIGN tions several noise-generating phenomena may occur simultaneously for example an impact press may generate noise not only because of the structural vibrations it produces but also because of the air it expels from between the impacting .