Automatic Recording Of The Frequency Characteristic Of The Llearing Aid; Instruction For Sandfilling - BRUEL & KJAER 4212 Instructions And Applications

1. Turn the METER RANGE knob on the AF Spectrometer until the meter
pointer of the Spectrometer deflects to a value between 0 and 20 db.
(If this cannot be obtained for any setting, turn the RANGE MULTIPLIER
knob of the Spectrometer, until the condition is obtained).
2. If the reading so obtained is between 0 and 10 dB, turn the RANGE
MULTIPLIER until a reading between 10 and 20 dB is obtained.
With a setting on the METER RANGE knob of the Spectrometer of "a"
dB SL, on the RANGE MULTIPLIER of "b" dB, and a meter reading of
"c" db, the sound pressure level P2 is
P2
=
a
+
b
+
c db re · 10-
4
,ubar.
The acoustical gain A at looo c/s is consequently
A
=
P2 - P1 db, where
P1 is the sound pressure level in the Test Box.
G. Automatic Recording of the Frequency Characteristic of the Hearing Aid.
1. Adjust the input Attenuator and the input Potentiometer on the Level
Recorder until the writing arm indicates 30
+
c mm, where "c" is the
instrument reading of the Spectrometer. The zero level on the recording
paper is then a
+
b - 30 db SL. "a" and "b" are the db SL-value
indicated on the METER RANGE and the dB-value indicated by the RANGE
MULTIPLIER, respectively.
2. Scan the frequency range from 150 c/s to 5ooo c/s on the B.F.O. and
check that the stylus deflection of the Level Recorder is within full
deflection. If this is not the case, readjust the knobs RANGE MULTIPLIER
and METER RANGE of the Spectrometer.
Note: One of the two positions "0 dB (x 1)" or "-10 dB (x o.3)" on the
RANGE MULTIPLIER
must
be used.
3. Set the frequency pointer of the BFO to looo c/s. Ref. Signal.
4. Adjust the Recording Paper so that the writing arm indicates 10 c/s,
by turning the grooved finger wheel to the right of the gearbox.
5. Set the AUTOMATIC SCANNING on the BFO in position "On".
6. Press the SINGLE CHART button on the Level Recorder.
The frequency range is now automatically scanned, and the frequency,
characteristic of the hearing aid drawn on the recording paper.
lnstmction for Sandfilling.
In Fig. 8, which is an exploded view of the Hearing Aid Test Box, is seen
which rooms should be filled with sand. Approximately 70 kg dry sand
is required, the total volume to be filled being 46.3 litres.
To take apart the Test Box apply the following procedure:
1. Unscrew the bolts marked A on Fig. 8.
2. Open the lid.
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