BRUEL & KJAER 2305 - Two Channel Recording of Acoustic Signals

By means of the facility included in the Level Recorder Type 2305, which
allows the recording pa per to be reversed by one chart length without losing
the synchronization between the BFO and the Spectrometer, the harmonics
are readily recorded on the same chart as the fundamental.
More details concerning the measurement are to be found in the manual
for the Hearing Aid Test Box Type 4212 (or 4217).
D O D aDO 0 0 0 0 0 0 0000 0 000 . 00 00 0000000 000 00 0 DO D O 0 0 0 a 0 DODO
" O ~ I .. r.~" _ ...... ...... . 11- , ..... . ..... 10 7$
-- -- ..
Measyring Qf
fund ame nt al 00 10
and harmonics
!O hearing olds :10 1S
QP 1123
10 100
...
Fundamental
2nd ha rm .
3rd harm . -;
1000 1 0000
16fB~ 1
Fig. 6.21. Example of recorded chart exhibiting the response of the fundamental
2nd and 3rd harmonics in a hearing aid.
Two Channel Recording of Acoustic Signals.
Two channel recording of acoustic signals can be carried out automatically
by using the B & K Two Channel Selector Type 4408 in conjunction with a
B
& K sound measuring system involving the Level Recorder . The two
channel recording method can, for instance, be used in laboratory or field
measurements of airborne sound insulation.
In Fig . 6.22 is illustrated an arrangement for automatic recording of the
airborne sound insulation of a wall between two offices . By this arrange-
ment the airborne sound insulation can be measured in accordance with the
1.S .O. Recommendation R 140. The transmitting part of the measuring
arrangement consists of the Random Noise Generator Type 1402, which is
co mbined with the Band-Pass Filter Set Type 1612, and a loudspeaker. If
n ecessary, a power amplifier can be used to obtain a signal level exceeding
the background noise by the required 10 dB. The Random Noise Generator
Ty pe 1402 is a signal source generating a noise signal in the frequency range
20-20000 Hz (cis) with Gaussian distribution up to 4 (] and with uniform
spectrum density ("white") . The Band-Pass Filter Set Type 1612 contains
33 filters with II.! octave bandwidth and 11 with lh octave. The Filter
Set has in this measuring set-up been combined with the Noise Generator