Recording Of The Frequency Response At Different Sound Levels; Visual Check On Frequency Characteristics - BRUEL & KJAER 4212 Instructions And Applications

and the Level Recorder are synchronized as described in the Instruction
Manual 1022. In Fig. 11 is shown a recording of the fundamental, the second,
the third, and the fourth harmonic produced in a hearing aid spectacle.
Recording of the Frequency Res. p onse at Different Sound Levels.
An alternative set-up for recording of frequency response curves is seen in
Fig. 12. Instead of the Spectrometer Type ·2112 is used the Microphone
Amplifier Type 2604. In this case the adjustment of the Level Recorder is
made by means of the output voltage from another Microphone Amplifier
Type 2604 in the compressor circuit, and the acoustical gain directly read off
the recording, when the amplification of the Microphone Amplifier Type 2604
is taken into account.
Visual Check on Frequency Characteristics.
If a quick visual check of the frequency response curve is desired (not a
permanent record) this can be obtained by substituting the Level Recorder
in the arrangements shown in Figs. 7 and 12 by a Frequency Response Tracer
Type 4 709. The compressor signal obtained from the amplifier in the regulating
microphone circuit is then used as an external frequency input to the Tracer
to give correct x-deflection even when the signal from the hearing aid is
20 c/s
300 400 500 100 lkc/1 LS 2
~-
10d8
20 c/1 30 .tO 50 70
100 300 400500 700 1'r.c/s L5 2
ft;!-9(6
Fig. 15. Sketch showing the screen of the Frequency Response Tracer Type
4709 during measurement.
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