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4.4 NOISE <br /> This section includes a description of acoustic fundamentals, existing noise conditions(e.g., existing noise- <br /> sensitive land uses and noise sources in the project vicinity), a summary of applicable regulations, and analyses of <br /> potential short-term and long-term noise impacts of the proposed project.Noise effects are evaluated according to <br /> the standards of the jurisdictions in which they are generated. Mitigation measures are recommended, as <br /> necessary,to reduce significant noise impacts. <br /> 4.4.1 ENVIRONMENTAL SETTING <br /> ACOUSTIC FUNDAMENTALS <br /> Noise is generally defined as sound that is loud, disagreeable,unexpected, or unwanted. Sound, as described in <br /> more detail below, is mechanical energy transmitted in the form of a wave because of a disturbance or vibration, <br /> and as any pressure variation in air that the human ear can detect. <br /> Sound Properties <br /> A sound wave is introduced into a medium(air)by a vibrating object. The vibrating object(e.g.,vocal cords,the <br /> string and sound board of a guitar,or the diaphragm of a radio speaker) is the source of the disturbance that <br /> moves through the medium. Regardless of the type of source creating the sound wave,the particles of the medium <br /> through which the sound moves are vibrating in a back-and-forth motion at a given frequency. The frequency of a <br /> wave refers to how often the particles vibrate when a wave passes through the medium. The frequency of a wave <br /> is measured as the number of complete back-and-forth vibrations of a particle per unit of time. If a particle of air <br /> undergoes 1,000 longitudinal vibrations in 2 seconds,then the frequency of the wave would be 500 vibrations per <br /> second. A commonly used unit for frequency is cycles per second,called hertz(Hz). <br /> Each particle vibrates as a result of the motion of its nearest neighbor. For example,the first particle of the <br /> medium begins vibrating at 500 Hz and sets the second particle of the medium into motion at the same frequency <br /> (500 Hz). The second particle begins vibrating at 500 Hz and thus sets the third particle into motion at 500 Hz. <br /> The process continues throughout the medium; hence each particle vibrates at the same frequency,which is the <br /> frequency of the original source. Subsequently, a guitar string vibrating at 500 Hz will set the air particles in the <br /> room vibrating at the same frequency(500 Hz),which carries a sound signal to the ear of a listener that is detected <br /> as a 500-Hz sound wave. <br /> The back-and-forth vibration motion of the particles of the medium would not be the only observable <br /> phenomenon occurring at a given frequency. Because a sound wave is a pressure wave, a detector could be used <br /> to detect oscillations in pressure from high to low and back to high pressure. As the compression(high-pressure) <br /> and rarefaction(low-pressure)disturbances move through the medium,they would reach the detector at a given <br /> frequency. For example, a compression would reach the detector 500 times per second if the frequency of the <br /> wave were 500 Hz. Similarly, a rarefaction would reach the detector 500 times per second if the frequency of the <br /> wave were 500 Hz. Thus,the frequency of a sound wave refers not only to the number of back-and-forth <br /> vibrations of the particles per unit of time but also to the number of compression or rarefaction disturbances that <br /> pass a given point per unit of time. A detector could be used to monitor the frequency of these pressure <br /> oscillations over a given period of time. The period of the sound wave can be found by measuring the time <br /> between successive high-pressure points (corresponding to the compressions) or the time between successive low- <br /> pressure points(corresponding to the rarefactions). The frequency is simply the reciprocal of the period; thus an <br /> inverse relationship exists so that as frequency increases,the period decreases, and vice versa. <br /> A wave is an energy transport phenomenon that transports energy along a medium. The amount of energy carried <br /> by a wave is related to the amplitude(loudness) of the wave. A high-energy wave is characterized by high <br /> amplitude; a low-energy wave is characterized by low amplitude. The amplitude of a wave refers to the maximum <br /> Manteca WQCF and Collection System Master Plans EIR EDAW <br /> City of Manteca 4.4-1 Noise <br />