1. Introduction to Noise Control
Environmental Science
Ithan B. Zimmer, Ph.D., P.E.

2. Basic Noise Control Environmental Noise Studies
Other Studies: Industrial, Theoretical, Mechanical
Environmental Impact Statements (EIS)
You need to understand the language
You can participate in an EIS
More background means it is harder to fool you

3. Famous Authors Leo Beranek (Father of Noise Control)
Cyril Harris (Handbook)
Karl Kryter (Effects)
Charles E. Wilson (NJIT)

4. Basic Noise Control Noise = unwanted sound
noise pollution is redundant
wasted energy
What defines noise is subjective
Environmental noise generally is transient

5. Possible Effects Hearing Loss Annoyance – Quality of Life Issues
Physiological Disorders
Psychological Disorders

6. Noise Measurement Decibel scale (dB)
Logarithmic, use common log, base 10
log xy = y log x
log (xy) = log x + log y
log (1/x) = - log x
log (x/y) = log x – log y
log 1 = 0

7. Sound Pressure Level (SPL)
SPL (dB) = 20 log (P/P0)
P = rms sound pressure
P0 = reference pressure 20 μPa
Threshold of Hearing = 0 dB
Threshold of Pain = 140 dB

8. Equation for Total Sound Pressure Level
SPLT = 10·log (10L1/ L2/10 + … Ln/10)
L1, L2 … are noise measurements in dB
Examples using table or equation
3 equal point sources of 50 dB, answer 54.8 dB
4 point sources of 60, 66, 62, 77. Answer 77.5 dB

9. Combining Noise Measurements
SPL Difference
Add to the Higher
3.0 1
2.5 2
2.1 3
1.8 4
1.5 5
1.2 6
1.0 7
0.8 8
0.6 9
0.5 10
0.4
> 10
Fig 14.4 in one edition

10. Loudness
An average individual perceives an increase in sound level of ~10 dB as a doubling in loudness.

11. Frequency Weighting There are multiple weighting systems
A-weighting is, by far, the most common
It is the best for environmental and community applications because it reflects human response.
Abbreviated dBA
Humans hear 20-20,000 Hz
Most sensitive from ,000 Hz
dBA Fig 14.5 in one edition
dBA – the A does NOT mean average alligator 50-4K; elephant 6-12K; dog 33K; rat 40K; cat 50K; bat; 7-98K; dolphin K

12. Metrics – Cumulative Noise Levels
LX – noise level exceeded X% of the time
L10
L50 – median noise level
L90 – background noise level
Transit/Highway applications

13. Equivalent Sound Level - Leq
Average over a period of time
Equations on the board
Day-Night Level: Ldn or DNL
An Leq for 24 hours with a 10 dBA penalty for night noise (10pm to 7am)
Used in community noise, especially airports
Airports must mitigate to below DNL 65
EPA outdoor to DNL 55, indoor DNL 45

14. Basic Noise Control Elements
Source
Receiver
Path
Environmental concern: air path, also structure
Sources: surface traffic, trains, aircraft, fans, machinery
Receiver: people

15. Noise Mitigation and Control
Reduce at the Source – almost always the best method
Increase or block the Path
Protect the Receiver

16. Noise Mitigation and Control
Source: engine design, exhaust control, friction reduction, # of vehicles
Path: noise barrier, increase the path, Land Use Management
Receiver: home treatment, hearing protection
85 dBA single hearing protection
104 dBA or 140 dBA pulse double hearing protection

17. Line Source vs. Point Source Double Distance = ?
SPL1 – SPL2 = 10 log (r2/r1)
SPL1 – SPL2 = 20 log (r2/r1)
Double from a line source such as traffic yields 3 dB drop
Double distance from a point source yields a 6 dB drop

18. Any Questions? Institute of Noise Control Engineering
Noise Pollution Clearinghouse
Environmental Protection Agency