This standard applies to steady@ broad-band@ narrow band. and/or discrete frequency sound at air temperatures between ?50??and +70?? The test duct diameter range is from 150 mm to 2 m. The maximum flow velocity in the duct is 30 m/s and the maximum swirl angle is 15??The frequency range is from 50 Hz to 10.000 Hz. This standard applies to sound sources connected to a duct. Examples of equipment covered by this standard are: (a) centrifugal fans@ (b) axial-flow fans@ (c) mixed-flow fans@ (d) air-handling units@ (e) unitary equipment@ (f) furnaces@ (g) dampers@ and (h) throttling devices. This standard does not apply to non-ducted equipment.