Svantek SV 977D - Page 369

369
SV 977D User Manual - Appendixes
NOTE 2 To ensure the above-mentioned uncertainty, ±1.5 dB, it is necessary to have a minimum number of
spectra with an averaging time of approximately 3 s. The number of spectra necessary to achieve the above-
mentioned uncertainty will depend on the variability of the noises. Investigations have shown that even with
strongly fluctuating noises (e.g. wind turbines), the number of spectra necessary does not generally exceed 12.
F.2.5. The tone adjustment
The value of the audibility can be used to determine whether or not a tone is prominent and if a tonal penalty
or adjustment is to be allocated to a certain source.
The tone adjustment is the audibility-depending function, that returns 7 different values. The table below shows
the corresponding K values:
The adjustment, Kt, is the value to be added to the value of L
Aeq
for a time interval to give the tone-corrected
rating level for that interval.
NOTE. Neither ISO/PAS 20065 nor ISO 1996-1 specifies at present how to determine the magnitude of the
tonal adjustment, K
T
. In the meantime, it is possible to determine K
T
from the mean audibility, ΔL, using abowe
table. ΔL is defined in ISO/PAS 20065.
F.3 DOCUMENTATION
As documentation for the analysis, the following information shall be given:
a) For the analysis:
• number of averaged spectra, measurement time period and effective analysis bandwidth, line
spacing,
• time window (e.g. Hanning), time weighting (Lin), and frequency weighting (A),
• one typical spectrum (at least) with an indication of the position of the critical band and the average
noise level in that band.
b) For the calculations in the decisive critical band:
• statement regarding whether the results were obtained by visual inspection (survey method) or by
automatic calculation (engineering method),
• frequency limits of the critical band and the range for the visual averaging or linear regression (see
C.4.3),
• frequencies and levels of the tones and the total tone level (Ls and Lt re 20 μPa in decibels),
• masking noise level in the critical band (L
G
re 20 μPa in decibels),
• audibility of the tones (ΔL
i
re 20 μPa in decibels),
• size of the adjustment (K in decibels).
c) For the averaged noise spectrum
• the mean audibility, (ΔL re 20 μPa in decibels),
• the extended uncertainty (U in decibels).