THE SCIENCE AND APPLICATIONS OF ACOUSTICS - H. H. Arnold ...

180 9. Sound-Measuring InstrumentationFigure 9.5. Sound pressure level corrections for conditions that deviate from the standardatmospheric pressure and temperature of 760 mmHg and 20 ◦ C.foam spheres that are placed over the microphones. However, these may not betoo effective if the wind speed exceeds 30 km/h (20 mph).Changes in atmospheric conditions, namely, temperature and pressure, maynecessitate corrections. Figure 9.5 illustrates a chart for determining correctionsdue to deviations from 1 standard atmosphere (762 mmHg or 30 in Hg) and 20 ◦ C,based on the following expression:(√ ( ) ) (√ ( ) ) F + 460 30 C + 273.3 760C T,P = 10 log= 10 log528 B293.3 B ′ (9.4)whereC T,P = correction factor to be added to the sound pressure level, dBF, C = temperature in ◦ For ◦ C, respectivelyB, B ′ = barometric in inches Hg or mmHg, respectivelyExample Problem 2For a sound pressure level, a reading of 92 dB is taken at the standard conditionsof 1 atmosphere and 68 ◦ F, predict the readings at 10 ◦ F and at 110 ◦ F for the sameatmospheric pressure.