This standard sets out in detail two laboratory methods for determining the sound power radiated by a device, machine, component or subassembly using a laboratory anechoic room having prescribedacoustical characteristics. While other methods could be used to measure the noise emitted by machinery and equipment, the methods specified in this standard are particularly useful for rating the sound output of sources which produce steady noise and for which directivity information on the source may be desired.The methods specified in this standard yield physical data that may be used for the following purposes:(a) Rating apparatus according to its sound power output.(b) Establishing sound control measures.(c) Predicting the sound pressure levels produced by a device in a given enclosure or environment. Techniques for utilizing the physical data for these special purposes are not included in this standard. The determination of the sound power radiated by a sound source in a completely free field or in a free field above a reflecting plane is based on the premise that the reverberant field produced by the source is negligible and that the total radiated power is obtained from the mean square sound pressure averaged in time and in space over a hypothetical sphere or hemisphere surrounding the source. The radius of the sphere or hemisphere is chosen so that its surface is in the far radiation field of the source.