Maico MA 50, Руководство по эксплуатации

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Operating Instructions MA 50
Geba_MA50_Fe_11a.doc 12 851 406/2 11/11
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.
-
Select the ear you like to test with the
channel
selector key

. For the opposite ear narrow band
masking noise is automatically set.
-
Adjust the required masking level with the
levelcontrol knob

.
- Notice that the masking sound is
continuously presented for effective
masking. You can interrupt the masking signal
by pressing the corresponding
interrupter key

.
- To mask when performing bone
conduction testing, place the headphone on the
opposite ear so that the receiver is at the correct
height (the sound output grid

exactly faces the
ear canal). Adjust the headband of the
headphones. The receiver on the side where the
bone conductor is placed should sit directly on the cheek bone.
The marking for air conduction with masking should be done with the
symbols

▲ the right side and

■the left side on the audiogram form. The
marking for bone conduction with masking should be done with the symbols
[ = the right side and ] = the left side on the audiogram form.
Picture 15 Headphone
Picture 16 correct seating of the
bone conductor