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<br />-. <br /> <br />Most sounds are not pure tones but a mixture of tones of varying amplitude, frequency, and <br />duration. The intensity of sound waves produce a sound pressure level, which is commonly <br />measured in a unit called the Decibel. The decibel is a logarithmic measurement used to <br />accommodate a numbering scheme that encompasses a large range of values. The logarithm is <br />used because the human ear can detect sounds more than a million times quieter than a jet aircraft <br />during take off. <br /> <br />Sound Pressure Level = 20 Log] 0 (Measured Sound Pressure / Reference Pressure) <br />Reftrence Pressure (Pref) = 0.00002 Newton s / {meter)2 <br /> <br />Decibel = The ratio between two quantities that are proportional to power. The <br />commonly used unit for measuring sound pressure levels. <br /> <br />Decibel Levels of Common Noise Sources <br /> <br />Many different properties affect the noise level of a specific source type. For example, three <br />lawn mowers may have three different noise levels because of differences in each specific piece <br />of equipment. Noise level also depends on the distance from the noise source and the attenuation <br />of the surrounding environment. <br /> <br />Figure 1.3 provides a rough estimate of decibel levels of some common noise sources. <br /> <br />Decibel Levels of Common Noise Sources <br /> <br />Sound Pressure Level (dBA) <br /> <br />1'10 ---------------------------------- <br />130 ---------------------------------- <br />120 ---------------------------------- <br />110 ---------------------------------- <br />100 ---------------------------------- <br />90 ---------------------------------- <br />80 ---------------------------------- <br />70 ---------------------------------- <br />60 ---------------------------------- <br />50 ---------------------------------- <br />'10 ---------------------------------- <br />30 ---------------------------------- <br />20 ---------------------------------- <br /> <br />Noise Source <br />Jet Engine (at 25 meters) <br />Jet Aircraft (at 100 meters) <br />Rock and Roll Concert <br />Pneumatic Chipper <br />Jointer/Planer <br />Chainsaw <br />Heavy Truck Traffic <br />Business Office <br />Conversational Speech <br />Library <br />Bedroom <br />Secluded Woods <br />Whisper <br /> <br />Figure 1.3 <br /> <br />5 <br />