Maico MA 53, Руководство по эксплуатации

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Operating Instructions MA 53
Geba_MA53_e_13a.doc 16 851 430/3 11/11
4.4 Masking of the opposite ear
The basics of masking are explained below. To begin testing immediately,
please go directly to 4.4.3 Manual masking.
4.4.1 Crossover:
When measuring a pure tone audiogram you assume that the measured
hearing threshold is correct. But if you recognize that sound is also
transmitted through bone conduction over the entire skull it is probable that
the opposite ear has also received sound. This is called “crossover”.
Crossover can also occur when measuring air conduction because a small
amount of air conducted sound is received by the skull and transmitted by
bone. Whether the crossover signal can heard by the opposite ear depends on
its inner ear function.
Relevant to crossover is the sound level which is received by the opposite ear.
The difference between the original test signal at the test ear and the received
signal at the opposite ear is called “interaural attenuation”.
For bone conduction measurement the interaural attenuation is 0 to 15 dB.
Bone conduction crossover is therefore possible even with a slight difference
in hearing loss between ears.
Important: Please advise the patient to tell you in which ear he hears the test
signal. It is thereby easier to detect crossover.
4.4.2 Masking theory:
To ensure that the patient will not experience crossover you must mask the
opposite ear. Masking increases the hearing threshold of the opposite ear.
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.
4.4.3 Manual masking:
If you have to mask use the common masking rules. See chapter 7 for
recommend literature.
Masking is an important part of practical audiometry. It is necessary to be
familiar with this topic to avoid errors which would lead to a wrong diagnosis.
For the opposite ear set the receiver selector

or

to AC and the signal
selector

or

to NOISE.
Adjust the required masking level with the level control knob

or

↕.