SOUND POWER MEASUREMENT PROCEDURES FOR FANS

Three basic acoustical measurement methods based on sound pressure mea surement are available to determine the sound power radiated from fans : the reverberation-room method, the free-held method over a reflectin g plane, and the in-duct method. The first two methods are to be used to determine the sound power radiated from the fan casing, the fan inl et, the fan outlet, or any combination thereof into free space. The in -duct method yields the sound power radiated by the fan inlet or outle t into a duct, and requires measurement of the acoustic pressure in a turbulent duct how environment. Three standardized measurement methods with engineering grade accuracy as applied to fans are described, i.e ., ISO 3743-1 (1994), ISO 3743-2 (1994), ISO 3744 (1994), and ISO 5136 (1990). Experimental results are presented for the differences betwee n the sound power spectra radiated from the inlet and the outlet of va rious fan types which were found by using the reverberation-room metho d, the free-held method, and the in-duct method.