noise pollution and control chapter 6. contents 1 introduction 2 effects of noise on people 3 rating...
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Noise Pollution and Noise Pollution and ControlControl
Chapter 6Chapter 6
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
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
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
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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
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]
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
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lg20
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
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
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101
lg10
101
lg10
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
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
6 Traffic noise prediction6 Traffic noise prediction
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
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
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
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
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
7.5 Protect the receiver7.5 Protect the receiver
• (1) When all else fails
• (2) Alter work schedule
• (3) Ear protection
Additional ReadingAdditional Reading
• E.B. Magrab, Environmental noise control, New York: Wiley, 1975
Discussion QuestionsDiscussion Questions
• 1. Define LN and Leq.
• 2. List the three basic elements and corresponding methods for the noise control.
•Thank you!