15-28 Accuracy Grade Model 831 Manual
Cu – Cu is the degree of curvature, and is a comparison of
the T20 and T30. Cu is expressed as the percentage
deviation from being perfectly in-line. See ISO 3382-
2:2008(E), Annex B.3.
SD – SD is the standard deviation of the measurement
results for the T30 or the T20 decay times. See equations 2
and 3 in ISO 3382-2:2008(E), Sections 7.1. For impulsive
excitation, n = 10 is used as defined in section 7.2
Accuracy Grade
ISO 3382-2:2008(E) describes three methods of differing
measurement uncertainty as follows:
Survey Method
The survey method is appropriate for the assessment of the
amount of sound absorption for noise control purposes, and
survey measurements of the airborne and impact sound
insulation. It should be used for measurements in ISO
10052. Survey measurements are made in octave bands only.
The nominal accuracy is assumed to be better than 10% for
octave bands.
Make measurements of the reverberation time for at least
one source position. Find the average of results from at least
two source-microphone combinations, see Table 15 - 3.
Engineering Method
The engineering method is appropriate for verification of
building performance for comparison with specification of
reverberation time or room absorption. It should be used for
measurements in ISO 140 (all parts) with remarks to
reverberation time measurements. The nominal accuracy is
assumed to be better than 5% in octave bands and better than
10% in one-third octave bands. See Table 15 - 3.
Measure reverberation time two or more times for each
source-microphone combination. At least six independent
source-microphone combinations are required, see Table 15
- 3 'Minimum Number of Positions and Measurements'.
Precision Method
The precision method is appropriate where high
measurement accuracy is required. The nominal accuracy is
assumed to be better than 2.5% in octave bands and better
than 5% in one-third-octave bands.
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