BRUEL & KJAER 2209 - Octave

phon(GDI
9
90
20-
::80
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t'\.~~ :"'.' ~ ~50
90 1 ro2 ~0 4' lo!:iio 710 900Hz' n I.L 1.8 2.24 ~:a 3. 55 4.5 56 9 o 1f2
1
kHz
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Fig.7 . 16. The spectrum of Fig.6.16 converted for loudness calculation
7 .4.2. Octave
Octave
analysis may be used to calculate the loudness of sounds in
diffuse
fields with relatively smooth spectra and containing no pure tones.
The procedure suggested by S.S. Stevens, is the second method described in
ISO recommendation 532.
Each Octave Band
Sound Pressure Level is transformed into a Loudness
Index (Fig.7.17). In the figure the frequency axis is calibrated in terms of
Band Centre Frequencies. The various Loudness Indices Sound are summed
using
the formula:
Where Sm is the highest Loudness Index and St is the Total Loudness in
sones (00). An example of the conversion and calculating process in shown
in Table 7.1.
102