BRUEL & KJAER 4111 - Controlling Frequency Response and Sensitivity

23
In fig.l4a both the American Standard Association and the European DIN
standardized curves for weighting networks to be employed in noise
m. easurements are given, together with the permitted tolerances. It
follows from this figure that it is possible to satisfy both standards
within the different prescribed tolerances. This fact is applied in
the microphone amplifier and the analyzers according to the curves of
fig. 14b. Both the Microphone Amplifier 2601 and the Analyzer 2109
incorporate the linear frequency characteristic (ASA curve C) and three
phon curves, Analyzer 2105 only the linear characteristic and the two
upper phon curves of fig. 13.
Noise measurements as well as noise recordings with the aid of Level
Recorder 2304 are carried out exactly as described under Sound Pres-
sure Level Measurements, only the appropriate weighting network is
connected, depending on the noise le, · el.
On the analyzers the noise
level is read off in phons as the sum of the meter indication in db +
the phon value as indicated at the "Voltage Range
11
knob + the factor
5
K = 20 log - (or (S-46) db) in which s is the microphone sensitivity
s
in mV /fbar and -S the same expressed in db re 1 volt/fbar. For
noise recordings the same procedure can be followed as explained on
p. 17 to obtain calibrated ordinate values on the recorder paper. It
should be kept in mind, however, that this calibration should be car-
ried out with the instrument on
11
Linear
11
and to switch over to the ap-
propriate phon curve afterwards.
CONTROL OF FREQUENCY RESPONSE AND SEN-
SITIVITY OF CONDENSER MICROPHONE 4111
When ordering a Condenser Microphone 4111 one may in addition order