This International Standard specifies a method for testing ducted fans and other air-moving devices todetermine the sound power radiated into an anechoically terminated duct on the inlet and/or outlet side of the equipment.NOTE 1 For the sake of brevity, wherever the term “fan” occurs in the text, it means “fan or other air-moving device”.The method is applicable to fans which emit steady, broad-band, narrow-band and discrete-frequency sound and to air temperatures between - 50 °C and + 70 °C. The test duct diameter range is from 0,15 m to 2 m. Test methods for small (d < 0,15 m) and large (d > 2 m) test ducts are described in the informative Annexes H and