2014-069 - Final Environmental Impact Report No. 2014-01

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HARBOR BLVD. MIXED USE TRANSIT CORRIDOR PLAN FINAL FIR CITY OF SANTA ANA 5. Environmental Analysis 5.9 NOISE This section discusses the fundamentals of sound; examines federal, state, and local noise guidelines, policies, and standards; reviews noise levels at existing receptor locations; and evaluates potential noise impacts associated with the Harbor Boulevard Mixed Use Transit Corridor Plan project. This analysis is based on noise calculations in Appendix G, Noise Monitoring and Modeling Data 5.9.1 Terminology and Noise and Vibration Descriptors Noise is most often defined as unwanted sound. Although sound can be easily measured, the perception of noise and the physical response to sound complicate the analysis of its impact on people. People judge the relative magnitude of sound sensation in subjective terms such as "noisiness" or "loudness." The following are brief definitions of terminology used in this chapter: ■ Sound. A disturbance created by a vibrating object, which, when transmitted by pressure waves through a medium such as air, is capable of being detected by a receiving mechanism, such as the human ear or a microphone. ■ Noise. Sound that is loud, unpleasant, unexpected, or otherwise undesirable. ■ Decibel (dB). A unitless measure of sound on a logarithmic scale. ■ A- Weighted Decibel (dBA). An overall frequency weighted sound level in decibels that approximates the frequency response of the human ear. ■ Equivalent Continuous Noise Level (1,J. The mean of the noise level averaged over the measurement period, regarded as an average level. ■ Day -Night Level (Lm). The energy average of the A- weighted sound levels occurring during a 24hour period, with 10 dB added to the sound levels occurring during the period from 10:00 PM to 7:00 AM. ■ Community Noise Equivalent Level (CNEL). The energy average of the A- weighted sound levels occurring during a 24 -hour period with 5 dB added to the levels occurring during the period from 7:00 PM to 10:00 PM and 10 dB added to the sound levels occurring during the period from 10:00 PM to 7:00 AM. L� and CNEL values rarely differ by more than 1 dB. As a matter of practice, L� and CNEL values are considered equivalent and are treated as such in this assessment. Characteristics of Sound When an object vibrates, it radiates part of its energy as acoustical pressure in the form of a sound wave. Sound can be described in terms of amplitude (loudness, frequency (pitch), or duration (time). The human October 2014 Page 5.9 -1