Norsonic nor140, Instructional Manual

Page: 163 / 220

145
Norsonic Nor140
Instruction Manual
145
Norsonic Nor140
Instruction Manual
Corner measurement for small rooms
For rooms with volumes less than 25 m3, the engineer-
ing Standard ISO 16283-1 requires additional meas-
urements in the corner of the receiving room. These
measurements are not possible with the Nor140 Build-
ing Acoustic mode.
However, by measuring the levels and reverbera-
tion time in mode 1 and mode 2 respectively, these
additional results may be included in the final calcula-
tion when transferred to the post-processing software
NorBuild or Nor850 BA-1.
Equalizing the excitation level
When measuring the airborne sound reduction it is in
some standards (e.g. section 5.1 Airborne sound field
in ISO 140.4 and ISO 10140) required that the varia-
tions in excitation spectrum is kept below certain as
flat as possible.
“The sound generated in the source room shall be steady
and have a continuous spectrum in the frequency range
considered. If filtering of the source signal is used, use
a bandwidth of at least one-third octave. If broad-band
noise is used (white noise is recommended), the spec-
trum may be shaped to ensure an adequate signal-to-
noise ratio at high frequencies in the receiving room. In
either case, the average sound spectrum in the source
room, at least above 100 Hz, shall not have differences in
level more than 6 dB between adjacent one-third octave
bands. See ISO 10140-4 and for equivalent alternatives
also ISO 18233.”
For this reason it is a possibility to insert a software spec-
trum shaper in the signal path of the noise generator.
This equalizer can attenuate each 1/3 octave band level
up to 12 dB. This equaliser is made to follow the above
mentioned requirements. If the level difference is less
than 6 dB between two adjacent frequencies, nothing
is done with the excitation signal with these two bands.
The equalizer must be turned on before it is used.
Then a measurement is performed and the result of
this measurement is used to calculate the attenua-
tion in each band. This is an automatic shaping of the
spectrum, optimised to preserve the energy of the ex-
citation signal.
Use the
SETUP 7
key sequence to activate the
Noise Generator control screen.
Move the cursor down to the “Equal: ON / OFF” line
and activate the equalizer with the Inc key. Then a new
line “Adj. equal” appears, and you can move the cur-
sor done to this line and push
ENTER
to activate the
shaping adjustments. When the equalization adjust-
ment is activated, the instrument starts a measurement
(with the selected measurement time, so it can be a
good idea to adjust this one before you start the equal-
izer, or you can stop the measurement manually after
the measured spectrum seems to be stable). After this
test measurement is finished, the instrument turns the
noise generator off and performs a special calculates
Noise Generator control screen