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Noise Pollution and Noise Pollution and Control Control Chapter 6 Chapter 6

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Page 1: Noise Pollution and Control Chapter 6. Contents 1 Introduction 2 Effects of noise on people 3 Rating systems 4 Community noise sources and criteria 5

Noise Pollution and Noise Pollution and ControlControl

Chapter 6Chapter 6

Page 2: Noise Pollution and Control Chapter 6. Contents 1 Introduction 2 Effects of noise on people 3 Rating systems 4 Community noise sources and criteria 5

ContentsContents

• 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

Page 3: Noise Pollution and Control Chapter 6. Contents 1 Introduction 2 Effects of noise on people 3 Rating systems 4 Community noise sources and criteria 5

1 Introduction1 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

Page 4: Noise Pollution and Control Chapter 6. Contents 1 Introduction 2 Effects of noise on people 3 Rating systems 4 Community noise sources and criteria 5

1 Introduction1 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

21

0

221

2 1

T

rms dttPT

pp

Page 5: Noise Pollution and Control Chapter 6. Contents 1 Introduction 2 Effects of noise on people 3 Rating systems 4 Community noise sources and criteria 5

1 Introduction1 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

Page 6: Noise Pollution and Control Chapter 6. Contents 1 Introduction 2 Effects of noise on people 3 Rating systems 4 Community noise sources and criteria 5

1 Introduction1 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]

Page 7: Noise Pollution and Control Chapter 6. Contents 1 Introduction 2 Effects of noise on people 3 Rating systems 4 Community noise sources and criteria 5

1 Introduction1 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]

N

jjp L

NL

1

20101

lg20

Page 8: Noise Pollution and Control Chapter 6. Contents 1 Introduction 2 Effects of noise on people 3 Rating systems 4 Community noise sources and criteria 5

2 Effects of noise on people2 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

Page 9: Noise Pollution and Control Chapter 6. Contents 1 Introduction 2 Effects of noise on people 3 Rating systems 4 Community noise sources and criteria 5

3 Rating systems3 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.

n

i

Leq

t tLeq

tt

L

dtt

L

i

1i

10

0

10

101

lg10

101

lg10

Page 10: Noise Pollution and Control Chapter 6. Contents 1 Introduction 2 Effects of noise on people 3 Rating systems 4 Community noise sources and criteria 5

4 Community noise sources and 4 Community noise sources and criteriacriteria

• 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

Page 11: Noise Pollution and Control Chapter 6. Contents 1 Introduction 2 Effects of noise on people 3 Rating systems 4 Community noise sources and criteria 5

5 Transmission of sound outerdoor5 Transmission of sound outerdoorss

• 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

Page 12: Noise Pollution and Control Chapter 6. Contents 1 Introduction 2 Effects of noise on people 3 Rating systems 4 Community noise sources and criteria 5

6 Traffic noise prediction6 Traffic noise prediction

Page 13: Noise Pollution and Control Chapter 6. Contents 1 Introduction 2 Effects of noise on people 3 Rating systems 4 Community noise sources and criteria 5

7 Noise control7 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

Page 14: Noise Pollution and Control Chapter 6. Contents 1 Introduction 2 Effects of noise on people 3 Rating systems 4 Community noise sources and criteria 5

7.1 Basic Elements7.1 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

Page 15: Noise Pollution and Control Chapter 6. Contents 1 Introduction 2 Effects of noise on people 3 Rating systems 4 Community noise sources and criteria 5

7.2 Control of noise source by 7.2 Control of noise source by designdesign

• (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

Page 16: Noise Pollution and Control Chapter 6. Contents 1 Introduction 2 Effects of noise on people 3 Rating systems 4 Community noise sources and criteria 5

7.3 Control of noise source by 7.3 Control of noise source by redressredress

• (1) Balance rotating parts

• (2) Reduce frictional resistance

• (3) Apply damping materials

• (4) Seal noise leaks

• (5) Perform routine maintenance

Page 17: Noise Pollution and Control Chapter 6. Contents 1 Introduction 2 Effects of noise on people 3 Rating systems 4 Community noise sources and criteria 5

7.4 Noise control in the 7.4 Noise control in the transmission pathtransmission path

• (1) Separation

• (2) Absorbing materials

• (3) Acoustical lining

• (4) Barriers and panels

• (5) Transmission loss

• (6) Enclosures

Page 18: Noise Pollution and Control Chapter 6. Contents 1 Introduction 2 Effects of noise on people 3 Rating systems 4 Community noise sources and criteria 5

7.5 Protect the receiver7.5 Protect the receiver

• (1) When all else fails

• (2) Alter work schedule

• (3) Ear protection

Page 19: Noise Pollution and Control Chapter 6. Contents 1 Introduction 2 Effects of noise on people 3 Rating systems 4 Community noise sources and criteria 5

Additional ReadingAdditional Reading

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

Page 20: Noise Pollution and Control Chapter 6. Contents 1 Introduction 2 Effects of noise on people 3 Rating systems 4 Community noise sources and criteria 5

Discussion QuestionsDiscussion Questions

• 1. Define LN and Leq.

• 2. List the three basic elements and corresponding methods for the noise control.

Page 21: Noise Pollution and Control Chapter 6. Contents 1 Introduction 2 Effects of noise on people 3 Rating systems 4 Community noise sources and criteria 5

•Thank you!