SU0015801 - Laserfiche WebLink

Home Browse Search

Acoustical Analysis Report Griffith Energy Storage Project Sound can be measured, modeled, and presented in various formats,with the most common metric being the equivalent sound level (Leq).The Leq has been shown to provide both an effective and uniform method for comparing time-varying sound levels and is widely used in acoustic assessments in the State of California. Estimates of noise sources and outdoor acoustic environments, and the comparison of relative loudness are presented in Table 1.Table 2 presents additional reference information on terminology used in the report. Table 1.Sound Pressure Levels and Relative Loudness of Noise Sources and Acoustic Environments Noise Source or Activity Sound Level Subjective Impression Vacuum cleaner(10 feet) 70 Passenger car at 65 miles per hour(25 feet) 65 Moderate Large store air-conditioning unit(20 feet) 60 Light auto traffic(100 feet) 50 Quiet Quiet rural residential area with no activity 45 Bedroom or quiet living room;Bird calls 40 Faint Typical wilderness area 35 Quiet library,soft whisper(15 feet) 30 Very quiet Wilderness with no wind or animal activity 25 High-quality recording studio 20 Extremely quiet Acoustic test chamber 10 Just audible 0 Threshold of hearing Adapted from:Kurze and Beranek(1988)and USEPA(1971) Table 2. Acoustic Terms and Definitions Term Definition Noise Typically defined as unwanted sound.This word adds the subjective response of humans to the physical phenomenon of sound.It is commonly used when negative effects on people are known to occur. Sound Pressure Level Pressure fluctuations in a medium.Sound pressure is measured in dB referenced to 20 pPa,the approximate (LP) threshold of human perception to sound at 1,000 Hz. Sound Power Level The total acoustic power of a noise source measured in dB referenced to picowatts(one trillionth of a watt). (Lw) Noise specifications are provided by equipment manufacturers as sound power as it is independent of the environment in which it is located.A sound level meter does not directly measure sound power. Equivalent Sound Level The Leq is the continuous equivalent sound level,defined as the single sound pressure level that,if constant (LQ over the stated measurement period,would contain the same sound energy as the actual monitored sound that is fluctuating in level over the measurement period. A-Weighted Decibel Environmental sound is typically composed of acoustic energy across all frequencies.To compensate for the (dBA) auditory frequency response of the human ear,an A-weighting filter is commonly used for describing environmental sound levels.Sound levels that are A-weighted are presented as dBA in this report. Unweighted Decibels Unweighted sound levels are referred to as linear.Linear decibels are used to determine a sound's tonality and (dBL) to engineer solutions to reduce or control noise as techniques are different for low and high frequency noise. Sound levels that are linear are presented as dBL in this report. Propagation and Propagation is the decrease in amplitude of an acoustic signal due to geometric spreading losses with Attenuation increased distance from the source.Additional sound attenuation factors include air absorption,terrain effects, sound interaction with the ground,diffraction of sound around objects and topographical features,foliage,and meteorological conditions including wind velocity,temperature,humidity,and atmospheric conditions. OTETRA TECH 3 August 2023