Maico MA 28 Operation Manuals - page 26
Operation Manual MA 28
8506915 Rev. 3
25
15/11/2017
5.6.2 Bone Conduction Testing
Place the bone conduction oscillator
on the patient’s head so that the flat, circular side
of the transducer is placed on the mastoid, at the noticeable ledge of the cranial bone
behind, but not touching the pinna. The other side of the headband is placed in front
of the opposite ear. Set the F1 key to Bone and select the test ear.
Perform the test utilizing the same method as air conduction testing.
5.6.3 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 dB 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 may increase the hearing threshold of the test ear. For bone conduction the
masking signal is automatically routed to the opposite output of the phones or inserts,
based on the test ear selected.
The masking is turned on by rotating the Masking Level dB level control dialto the
right. The masking sound should be continuously presented for effective masking. 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.
Adjust the level of the masking noise for the appropriate level to be presented.
When the Store button is pressed, the hearing threshold value will be stored with the
masking level.
5.6.4 Auto Threshold (Hughson-Westlake)
– Air Only
In addition to traditional manual testing, the MA 28 incorporates a Hughson-Westlake
patient controlled automatic threshold test complying with ISO 8253 for air conduction
thresholds only. The test results are stored within a table display on the device.
Hughson-Westlake is a procedure used to determine pure tone thresholds. The MA 28
utilizes this procedure to perform an automatic pure tone test procedure (air conduction
only). Threshold is defined as 2 out of 3 (or 3 out of 5) correct responses obtained at a
certain level in a 10 dB decrease and 5 dB increase procedure. The test frequencies will
start at 1000 Hz and continue through those frequencies activated within the settings.
The device will re-test 1000 Hz before moving to the next ear or ending the test.
The test is accessed through the function keys in the 3
rd
menu selection. From the
main test screen Press F4 (More) until HW is displayed at F1. The HW Test will always
display a table for results to be viewable during the test and after.