This International Standard specifies the acoustical performance requirements for reference sound
sources:
— temporal steadiness (stability) of the sound power output;
— spectral characteristics;
— directivity.
Temporal steadiness is defined in terms of the standard deviation of repeatability (see 5.2). The
spectral characteristics can be verified in either a hemi-anechoic room or a reverberation test room
from measurements of the frequency band sound power levels in accordance with this International
Standard (see 5.4). The performance requirements on directivity index can only be verified in a hemianechoic
room (see 5.5.)
This International Standard also specifies procedures for providing level calibration data and
uncertainty on a sound source intended for use as a reference sound source in terms of its sound power
level under reference meteorological conditions as defined in Clause 4 in octave and in one-third-octave
bands, and with frequency weighting A.
This International Standard is titled as a calibration standard even though the method is conducted in
a testing laboratory and the level calibration results are not directly traceable to national standards of
measure in a strict metrological sense. Testing laboratories performing this method are not expected
to meet all requirements normally associated with a calibration laboratory.