SU0015801 - Laserfiche WebLink

Home Browse Search

4 Environmental Analysis 4.13 Noise 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 as well as a comparison of relative loudness are presented in Table 4.13-1. Table 4.13-2 presents additional reference information on terminology used in the report. Table 4.13-1. Sound Pressure Levels (LP) and Relative Loudness of Typical Noise Sources and Acoustic Environments Sound Level Noise Source or Activity (dBA) 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 Extremely quiet High-quality recording studio 20 10 Just audible Acoustic test chamber 0 Threshold of hearing Adapted from:Kurze and Beranek(1988)and USEPA(1971). Table 4.13-2. 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(LP) Pressure fluctuations in a medium.Sound pressure is measured in d6.Referenced to 20 micropascals (pPa),the approximate threshold of human perception to sound at 1,000 Hertz(Hz). Sound Power Level(Lw) The total acoustic power of a noise source measured in dB referenced to picowatts(one trillionth of a watt).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(Leq) The Leq is the continuous equivalent sound level,defined as the single sound pressure level that,if constant 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(dBA) Environmental sound is typically composed of acoustic energy across all frequencies.To compensate for the 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 Decibel(dBL) Unweighted sound levels are referred to as linear.Linear decibels are used to determine a sound's tonality and 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. Griffith Energy Storage Project 4.13-2 Tetra Tech/2022120675 Draft Environmental Impact Report August 2023