American National Standard Acoustics – Determination of sound power levels
and sound energy levels of noise sources using sound pressure – Precision
methods for anechoic rooms and hemi-anechoic rooms - Nationally Adopted
International Standards
This American National Standard specifies methods for measuring
the sound pressure levels on a measurement surface enveloping a
noise source (machinery or equipment) in an anechoic room or a
hemi-anechoic room. The sound power level (or, in the case of
impulsive or transient noise emission, the sound energy level)
produced by the noise source, in frequency bands of width one-third
octave or with frequency weighting A applied, 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 acoustic impedance.
In general, the frequency range of interest includes the
one-third-octave bands with mid-band frequencies from 100 Hz to
10,000 Hz. In practice, the range is extended or restricted to
frequencies beyond or within these limits, to those between which
the test room is qualified for the purposes of the
measurements.
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. The maximum size of the noise source depends on
specified requirements regarding the radius of the hypothetical
sphere or hemisphere used as the enveloping measurement
surface.
Test room
The test rooms that are applicable for measurements made in
accordance with this American National Standard are an anechoic
room or hemi-anechoic room, also called, respectively, a free-field
test room or hemi-free-field test room.
Measurement uncertainty
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 limited bands
of frequency and with frequency weighting A applied. The
uncertainty conforms to ISO 12001:1996, accuracy grade 1 (precision
grade).