2865 (RP-339) -- Relationship between Sound Power Level and Sound Pressure Level in Dwellings and Offices PDF

The Diffuse Field Theory of sound propagation indoors does not work for typical furnished rooms in dwellings and offices.
An alternative simple empirical relationship has been found that predicts with considerable accuracy the sound pressure level, Lp, in such rooms, based on the sound power level, Lw, of the source, the room volume, V, the frequency, f, and the distance, r, from the source:

L_p = L_w – 10 log r_(ft) – 5 log V_{(cu ft)} – 3 log f_(Hz) + 25 (dB)

If this new relationship is accepted, there are serious implications for our current standard test procedures for field measurements in occupied buildings. Since the room absorption, A, does not appear explicitly in the formula, the customary normalization with10 log (A/A_o) in transmission loss and impact noise tests is probably incorrect In addition, since no uniform reverberant sound field occurs in normally furnished spaces, it is not clear what one ought to measure for the receiving-room sound pressure level in tests of transmission loss, noise reduction, and impact noise.