A round robin study of sound power measurement methods to determine reproducibility and bias

Three different sound power measurement methods are common in the heating, ventilation, and air-conditioning industry: free field method, diffuse field method, and sound intensity method. An inter-laboratory round robin study is being conducted to quantify the reproducibility and bias of these three measurement methods. A loudspeaker source has been sent to at least 15 testing facilities in the United States, and its sound power measured by the preferred test methods applied in those facilities. Both a broadband signal with a decreasing slope of -5 dB per octave band and the same signal with four discrete frequency tones at 58, 120, 300, and 600 Hz are used in the measurements. The measured sound power levels across one-third octave bands have been compared within a lab facility, between lab facilities using the same method, and between measurement methods. The project is still ongoing, with data collection continuing at additional test facilities so that repeatability, reproducibility, laboratory bias, and measurement method biases may be rigorously determined according to ISO 5725.