Perceived Level of Noise by Mark VII and Decibels (E)

The calculation procedure Mark VII gives the perceived level of loudness or noisiness in PLdB. It utilizes a set of frequency-weighting contours based on an average of 25 experimental contours. The standard reference sound is defined as a 13-oct band centered at 3150 Hz. The perceived magnitude (loudness or noisiness) grows as the 23 power of the sound pressure, so that perceived magnitude doubles with each increase of 9 dB. The summation formula for the total subjective magnitude remains St = Sm + F (∑S − Sm), but the value of F is made to vary as a function of level in order to reflect the nonlinear growth (in log-log coordinates) of broad-band noise. As a result of the new reference sound at 3150 Hz, perceived level in decibels (PLdB) is approximately 8 dB lower than the older loudness level in phons. Except for the nearly constant difference of 8 dB, Mark VI and Mark VII give closely similar results for typical broad-band noises. The 8-dB downward shift makes it possible for a sound level meter with an “ear weighting” to give readings (E) in decibels within a decibel or two of perceived level in PLdB. With the frequency-weighting contours extended down to 1.0 Hz, Mark VII also provides a procedure for calculating the perceived levels of sonic booms and other impulse noises.