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Assessing and Mitigating Noise Impacts  

Author:  | New York, Noise

These noise guidelines include an excellent primer.

Table A
APPROXIMATE ADDITION OF SOUND LEVELS

Difference Between Two Sound Levels  Add to the Higher of the Two Sound Levels
≤1 dB  3 dB
2-3 dB  2 dB
4-9 dB  1 dB
≥10 dB  0 dB

(United States Environmental Protection Agency, Protective Noise Levels, Condensed Version of EPA Levels document, EPA 550/9-79-100, November 1978, Office of Noise Abatement & Control, Washington, D.C.)

“[T]wo proximal noise sources that are 70 dBA each do not have a combined noise level of 140 dBA. In this case the combined noise level is 73 dBA.”

“SPL increases approaching 10 dB result in a perceived doubling of SPL. … An increase of 10 dB(A) deserves consideration of avoidance and mitigation measures in most cases. … In general, the EPA’s “Protective Noise Levels” guidance found that ambient noise levels # 55 dB(A) L(dn) was sufficient to protect public health and welfare and, in most cases, did not create an annoyance (EPA 550/9-79-100, November 1978). In non-industrial settings the SPL should probably not exceed ambient noise by more than 6 dB(A) at the receptor. An increase of 6 dB(A) may cause complaints.”

[Note that L(dn), the day-night average sound level, is generally calculated with adding 10 dB to values measured at night, i.e., an L(dn) of 55 dB(A) implies an average night level of 45 db(A).]

Table B
HUMAN REACTION TO INCREASES IN SOUND PRESSURE LEVEL

Increase in Sound Pressure (dB)  Human Reaction
<5  Unnoticed to tolerable
5-10  Intrusive
10-15  Very noticeable
15-20  Objectionable
>20  Very objectionable to intolerable

(Down, C.G. and Stocks, J.; Environmental Impact of Mining. Applied Science Publishers Ltd., ISBN 0853347166, 1978)

Table C
PROJECTED NOISE LEVELS

Noise Source  Measurement  1,000 feet  2,000 feet  3,000 feet
Primary and secondary crusher  89 dB(A) at 100 ft  69.0 dB(A)  63.0 dB(A)  59.5 dB(A)
Hitachi 501 shovel loading  92 dB(A) at 50 ft  66.0 dB(A)  60.0 dB(A)  56.5 dB(A)
Euclid R-50 pit truck loaded  90 dB(A) at 50 ft  64.0 dB(A)  58.0 dB(A)  54.4 dB(A)
Caterpillar 988 loader  80 dB(A) at 300 ft  69.5 dB(A)  63.5 dB(A)  60.0 dB(A)

(Barksdale, R.D., editor, 1991. The Aggregate Handbook: National Stone Association [Washington, DC], 1.V)

“At distances greater than 50 feet from a sound source, every doubling of the distance produces a 6 dB reduction in the sound.” [The reduction may be only 3 dB per doubled distance for low-frequency sound and for a “line” source.]

[Most manufacturers do not publish the noise levels of their machines, with the following exceptions:
Clipper 2.5 MW Wind Turbine – SPL @8 m/s [~40% capacity]: 104 db(A), according to IEC 61400-11
Nordex N90/2500 – at 95% red. nominal output: 104.5 dB(A) [LS model]/107 dB(A) [HS model]]

Download original document: “Assessing and Mitigating Noise Impacts

This article is the work of the author(s) indicated. Any opinions expressed in it are not necessarily those of National Wind Watch.

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