BRUEL & KJAER 2204 - Filter Characteristics

With Microphone Amplifier Type 2604.
The amplifier itself loads the filters correctly and no additional shunt
resistor is needed. Therefore the cable AO 0034 must be used from the filter
output. The shunted cable, AO 0035 may be used for the filter input without
affecting performance.
Fllter Characteristics.
The cut -o ff frequencies ft and f2 (3 dB attenuation) of the filters are equal
distances away from the centre frequency fo on a logarithmic scale. Thus
ft == fo I v2. f2 == fo v2 and f2 ==2ft i.e. an octave filter with centre , frequency
1ooo Hz has cut-off frequencies 707 and 1414 Hz. The shape of the attenu-
ation curves is seen from Fig. 3.2. Inside the pass-band the response
is flat to within ± o.5 dB and outside the 3 dB attenuation points the slope
of the characteristic is about 45-50 dB/Octave. One octave away from the
cut-off frequency the attenuation is approximately 40 dB. A complete set of
filter characteristics is shown in Fig. 3.3.
I
dB
r
"'
I
\
Max. steepness:
45 -so dB/octave
I
10
\
20
v
\
I
30
\
I
\
I
40
\
v
50
I\
60
Fig. J.2. Filter characteristic of one of the octave filters.
16