Operating Instructions MA 41
8100456_OI_MA41_EN_15a 16 8100456-8 04/15
5.1.1.1 Masking
Masking is required if there is a notable threshold difference between the left
and right ears. It is possible for sound to be transmitted to both ears via bone
conduction while testing the poorer ear. This is called “crossover.”
Crossover occurs often while testing bone conduction, but it can also occur
during air conduction testing. Relevant to crossover is the sound level received
by the opposite ear. The difference between the original test signal in the test
ear and the received signal in the opposite ear is called “interaural attenuation.”
For bone conduction measurements the interaural attenuation is 0 to 15 dB.
Bone conduction crossover is therefore possible even with a slight difference in
hearing loss between ears.
To ensure that the patient will not experience crossover, mask the opposite ear.
Masking increases the hearing threshold of the opposite ear. For bone
conduction the masking signal is automatically routed to the opposite output
of the phones or inserts.
The masking is done with a noise signal which is transmitted by the headphone.
For pure tone audiometry a narrowband noise is used. This noise changes its
center frequency according to the frequency of the test signal.
Manual Masking
The masking is switched on by pressing the Masking On/Off button (15). The
channel of the non-test ear is switched on and set to noise with a level
of 0 dB
HL
.
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