ID: 1614 / ver. 210
4 Operation
If nothing else mentioned, the description will be for both channels.
4.1 Attenuators
By applying light pressure to the DOWN/UP
buttons
the attenuator steps up or down.
The actual sound level can be read in the two attenuator
displays.
Normally the steps are 5 dB, but by means of the 1 dB button the steps can be changed to 1 dB.
Held down for a while, the attenuators will repeat.
The attenuators are click free, meaning that you may change sound level while the attenuators are active, without
loosing the signal. However, there is a reservation to this: Say you start at 60 dB at 1000 Hz and hold down the
interrupter while increasing the hearing level. In this case you will not be able to rise hearing level to 120 dB, without
releasing the interrupter.
This has the following reason:
In order to decrease amplifier noise at low hearing levels, the signal to the earphones is attenuated by 20 dB by a
resistor. When a high level is needed the resistor is shorted by a relay. This must happen while the earphone is silent,
or a loud click will be heard. If the operator wants to increase hearing level near to maximum you need to release the
interrupter, increase hearing level, and activate the interrupter again. The same applies when you want to decrease
from a high to a low level - you also need to release the interrupter. In this case it will be at a sound level 25 dB lower
than when increasing the level.
To be able to increase hearing level without the relay shortening, you must do the following:
An example: Anticipate that the attenuator is set on 40 dB; consequently the relay is switched off. You want to
perform a manual tone decay test which moves over 20 dB and starts at 85 dB. Press the attenuator up to 105 dB (20
dB higher than the starting point) to ensure the relay will short. Now set the attenuator back to 85 dB where you
want the test to start. Because of the 25 dB difference in the relay switching point, the relay will stay shorted. You
may now activate the interrupter and move attenuator from 85 to 105 dB without any cut-offs.
The 1 dB button
By means of the 1 dB button
you may select steps of 1 dB
for the attenuator
.
The light will shine as long as the
1 dB function is active.
As mentioned you may change hearing level while interrupters are active. When the 1 dB steps are active the change
is made over 200 msec. instead of the usual 50 msec. making it impossible to hear any sharp increase of hearing level.
Please note that the attenuator may be a little slow when running 1 dB, and the interrupter is activated.
5 dB:
The 5 dB is performed over 50 msec. smooth as the 1 dB increase, e.g. for tone decay tests.
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