ASA - ANSI/ASA S12.51/ISO 3741
American National Standard Acoustics – Determination of sound power levels and sound energy levels of noise sources using sound pressure – Precision methods for reverberation test rooms
|Publication Date:||1 January 2012|
This American National Standard specifies methods for determining the sound power level or sound energy level of a noise source from sound pressure levels measured in a reverberation test room. The sound power level (or, in the case of noise bursts or transient noise emission, the sound energy level) produced by the noise source, in frequency bands of width one-third-octave, is calculated using those measurements, including corrections to allow for any differences between the meteorological conditions at the time and place of the test and those corresponding to a reference characteristic impedance. Measurement and calculation procedures are given for both a direct method and a comparison method of determining the sound power level and the sound energy level.
In general, the frequency range of interest includes the one-third-octave bands with mid-band frequencies from 100 Hz to 10 000 Hz. Guidelines for the application of the specified methods over an extended frequency range in respect to lower frequencies are given in Annex E. This American National Standard is not applicable to frequency ranges above the 10 000 Hz one-third-octave band.
NOTE For higher frequencies, the methods specified in ISO 9295 can be used.
Types of noise and noise sources
The methods specified in this American National Standard are suitable for all types of noise (steady, nonsteady, fluctuating, isolated bursts of sound energy, etc.) defined in ISO 12001.
The noise source under test can be a device, machine, component or sub-assembly. This American National Standard is applicable to noise sources with a volume not greater than 2 % of the volume of the reverberation test room. For a source with a volume greater than 2 % of the volume of the test room, it is possible that the achievement of results as defined in ISO 12001:1996, accuracy grade 1 (precision grade) is not feasible.
NOTE In specific cases, the source volume can be increased to a maximum of 5 % of the room volume. In such cases, the relevant noise test code indicates the possible consequences on the measurement uncertainty.
Reverberation test room
The test rooms that are applicable for measurements made in accordance with this American National Standard are reverberation test rooms meeting specified requirements (see Clause 5).
Information is given on the uncertainty of the sound power levels and sound energy levels determined in accordance with this American National Standard, for measurements made in specific frequency bands and for the A-weighted sum of all frequency bands. The uncertainty conforms to ISO 12001:1996, accuracy grade 1 (precision grade).