BRUEL & KJAER 2305 - Page 87

meter Type 2112. The swit c hing over can be carried out manually or
remotely . The A.F. Spectrometer Type 2112 has, among other things, input
facilities for the B & K Condenser Microphones, output facilities for the
Level Rec order and includes % and * octave ba nd-pass filters which are
identical to those in the Ba nd-Pass Filter Set Type 1612 mentioned above .
As the whole measuring a rrangement oprrates automatically the various
remote switchings are controlled from the Level Recorder .
A
recording from such an investigation can be seen in Fig. 6.23. All the
nearly ver tical lines do not belong to the measuring res ult as they are due
to the movement of the writing pen in the switching over period, i.e. to the
shifting from the level in the source room to th at in the receiving room
and vice vers a. The upp er envelope repr e sents the sound pressure level of
the radiated noise in the source room as measured in % octave bands. The
lower e nvelope gives the % octave level radiated in the receiving room.
-
ooo oo ooo o ooo oo oooo OOOOO OO D O O OOO Oo oo o ooooooo o oooo o o
BrO ~ J "' +
~ .....
_ .... _ . ...
,","
~
~ 50urid pressure ~
IAIA
i
in source ~
f tl'
'UU !" .
i=
loi-
I"
I-
: SC
;ounc . 1" ~~:"U'
I"
In recle-
-
: ving room .
............ f .... SooIo ~, ~
OP 1123
..,.--
.
1'00 -
1 00 0 CIS
'r.li~
162297
Fig. 6.23. Two channel record 01 the sound pressure levels in the two ol/ices.
The loudspeaker response at the higher frequencies was inadequate so the
level in the rec e iving room at these frequencies dropped below the Level
Recorder 's 50 dB range used. The levels regis tered at "A", " B" , "C" and "Lin"
on the ch a rt are the background noise in the two rooms respectively, as
measured by the "A", "B", "C" and "Lin" weighting ne tworks .
The sound level difference between the two rooms can be read as a function
of frequency directly fr om the recording in Fig. 6.23. For the purpose of
illustration this difference is plotted in Fig. 6.24. When appropriate com·
pensation is applied for the absorption in the receiving room , the normalized
level differ ence can be calculated in accordance with the mentioned I.S.0 .
Recommenda tion .
86