Noise Pollution and Control Chapter 6 Noise Pollution and Control

Contents 1 Introduction 2 Effects of noise on people 3 Rating systems 4 Community noise sources and criteria 5 Transmission of sound outerdoors 6 Traffic noise prediction 7 Noise control

1 Introduction 1.1 Overviews Unwanted sound  Environmental pollutants and potential hazard (1) subjective (2) short decay time (3) insidious (阴险的，隐伏的) (4) as a part of the price of progress

1 Introduction 1.2 Properties of sound waves (1) Sinusoidal wave [Figure] (2) speed of sound, v (3) Period or frequency, P or f (4) wave length, λ P=1/f λ =c/f (5) Amplitude and prms

1 Introduction 1.3 Sound power and intensity (1) sound power (2) sound intensity I=W/A I=(prms)2/ρc c=20.05(T)1/2

1 Introduction 1.4 Sound levels and decibel (1) sound levels L=10lg(Q/Q0) Unit: dB (2) sound power levels: Reference 10-12 Lw=10lg(W/10-12) sound intensity levels: Reference 10-12 LI=10lg(I/10-12) sound pressure levels: Reference 20uPa Lp=10lg(prms/prms0)2 [Figure Relative scale of sound pressure levels]

1 Introduction 1.5 Characterization of noise (1) Weight networks (2) Octave bands (3) Averaging sound pressure levels (4) Types of sounds -steady state -continuous -intermittent -impulse: [Figure]

2 Effects of noise on people 2.1 Hearing damage (1) Range: 20-20000Hz (2) Loudness (3) Damage-Risk Criteria 2.2 Speech interference 2.3 Annoyance 2.4 Sleep interference 2.5 Performance or work efficiency 2.6 Acoustic privacy

3 Rating systems 3.1 Goals of a noise rating systems 3.2 LN concept The parameter LN is a statistical measure that indicates how frequently a particular sound level is exceed. 3.3 Leq concept The Leq is a constant noise level that, over a given time, expends the same amount of energy as the fluctuating level over the same time period.

4 Community noise sources and criteria 4.1 Transportation noise -Aircraft noise -Highway vehicle noise 4.2 Internal combustion engines 4.3 Construction noise 4.4 Levels to protect health and welfare -Ldn<45dB

5 Transmission of sound outerdoors 5.1 Inverse square law 5.2 Radiation fields of a sound source 5.3 Directivity 5.4 Airborne transmission -Effects of atmospheric conditions -Basic point source model -Sound power level unknown

6 Traffic noise prediction

7 Noise control 7.1 Basic elements 7.2 Control of noise source by design 7.3 Control of noise source by redress 7.4 Noise control in the transmission path 7.5 Protect the receiver

7.1 Basic Elements (1) Source -Modifying the source to reduce its noise output (2) Path -Altering or controlling the transmission path and the environment to reduce the noise level reaching the listener (3) Receiver -Providing the receiver with personal protective equipment

7.2 Control of noise source by design (1) Reduce impact forces (2) Reduce speeds and pressures (3) Reduce frictional resistance (4) Reduce radiating area (5) Reduce noise leakage (6) Isolate and dampen vibrating elements (7) Provide mufflers and silencers

7.3 Control of noise source by redress (1) Balance rotating parts (2) Reduce frictional resistance (3) Apply damping materials (4) Seal noise leaks (5) Perform routine maintenance

7.4 Noise control in the transmission path (1) Separation (2) Absorbing materials (3) Acoustical lining (4) Barriers and panels (5) Transmission loss (6) Enclosures

7.5 Protect the receiver (1) When all else fails (2) Alter work schedule (3) Ear protection

Additional Reading E.B. Magrab, Environmental noise control, New York: Wiley, 1975

Discussion Questions 1. Define LN and Leq. 2. List the three basic elements and corresponding methods for the noise control.

Thank you!