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Calculate the sound pressure level this way: 410 <br /> 2 <br /> P <br /> SPL = 10 log measured 1 <br /> Preference <br /> TABLE I. SOUND PRESSURES AND ASSOCIATED SOUND PRESSURE LEVELS, <br /> Sound Pressure Sound Pressure <br /> (Microbars) Level (Decibels) <br /> 200 120 <br /> 0.02 40 <br /> 0.0002 0 <br /> 41/ <br /> . <br /> Because decibels are logarithmic quantities , it takes a tenfold <br /> change in the ratio of the square of the sound pressure to the square of <br /> the reference sound pressure to result in a 10-dB change in sound <br /> pressure level. A doubling of the ratio of the squares of the pressures <br /> results in a 3-dB change in sound pressure level . <br /> Sound pressure levels can be easily measured . To do so , <br /> acousticians use a sound level meter , an instrument which , like the <br /> human ear , is sensitive to sound pressure. A sound level melter relates <br /> the sound pressure of a incident sound wave to the standard reference <br /> pressure. A sound pressure level of 0 dB (i .e. , the measured sound <br /> 1 <br /> pressure equals the reference pressure) represents approximately the <br /> weakest sound that can be heard by the average young human ear in the <br /> frequency region of highest sensitivity. At the other end of the <br /> hearing range , humans feel physical pain in their ears when the sound <br /> (10 <br /> 6 <br /> „ <br />