3.1 Land Use
3.13
NOISE
3.13.1 Introduction
Noise is defined as unwanted or objectionable sound. The effects of noise on people can include
general annoyance, interference with speech communication, sleep disturbance and, in the extreme,
hearing impairment.
Noise Terminology
The human ear is not equally sensitive to all frequencies within the sound spectrum. Therefore, a
method called "A-weighting" is used to filter noise frequencies that are not audible to the human
ear. Noise levels are usually measured and expressed in decibels (dB) and noise levels using the
"A-weighted" noise scale are usually written dB(A) or dBA. Decibels are measured on a logarithmic
scale which quantifies sound intensity in a manner similar to the Richter scale used for earthquake
magnitudes. Thus, a doubling of the energy of a noise source, such as doubling traffic volume,
would increase the noise level by 3 dBA; a halving of the energy would result in a 3 dBA decrease.
Table 3.13-1 shows the relationship of various sound levels to commonly experienced noise events.
Average noise levels over a period of minutes or hours are usually expressed as dB Leq, or the
equivalent noise level for that period of time. The period of time average may be specified; Leq(3)
would be a three hour average; when no period is specified, a one hour average is assumed.
Construction noise standards are usually stated as average noise levels over a period of 1, 8 or 12
hours.
Noise standards for land use compatibility have been established by various jurisdictions, and in
California are usually stated in terms of the Community Noise Equivalent Level (CNEL), which is a
24-hour weighted average measure of community noise. The computation of CNEL adds 5 dB to the
average hourly noise levels between 7 p.m. and 10 p.m. - the evening hours, and 10 dB to the average
hourly noise levels between 10 p.m. and 7 a.m. - the nighttime hours. This weighting accounts for
the increased human sensitivity to noise in the evening and nighttime hours. A similar 24-hour
weighted average is the Day-Night Average noise level (Ldn or DNL), which weights only the
nighttime hours, and not the evening hours. CNEL is used primarily in California.
Regional Beach Sand Project EIR/EA
Page 3.13-1
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