Standard deviation in power measurements on small measurement surfaces with use of the free field method

Abstract

Standard deviation in sound power measurements made by the free field method on a small measurement surface is discussed. The authors numerically investigated ISO 3745 describing the measurement surface radius. Although sound source models were simplified here, the authors confirmed numerically that ISO 3745 is reasonable. There is a “biased” deviation in the sound power measurements with use of a small measurement surface. This biased deviation, however, can be reduced to within 0·25 (about 1 dB), when ISO 3745 is employed. Standard deviations estimated from intensity data were also investigated. There is no biased deviation in the sound power measurements with use of the intensity technique.