USING THE AUDIOMETER (OVERVIEW)
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OM033-4 - CA850 Series 5 Operating Manual
3.3
TESTING THE PATIENT RESPONSE SWITCH
Press the patient response switch and the indicator labelled RESPONSE (to the right of the display) will
illuminate green.
3.4
USING THE TALKOVER FUNCTION
The CA850
is equipped with a Talkover function using the built in microphone to the left of the display. Press
and hold the TALK OVER button to
interrupt the test and route the operator’s voice to the patient headset.
Adjust the volume level using the
and
keys while the button is pressed. The Talkover function is indicated
at the top of the display along with the volume level while the TALK OVER button is held down.
Release the button when Talkover has been completed, and use the indicated softkeys to repeat the frequency
that was being tested, move to the next frequency or cancel the test.
3.5
TEST TYPES AVAILABLE
Refer to Sections 4 & 5 for details of a typical test arrangement and a suggested test procedure with
operational sequence. Refer also to the appropriate audiometric standards.
3.5.1 Manual Test
Hearing thresholds may be recorded manually using the Plot point function. When used this will record a
threshold for the currently selected ear at the frequency and sound level indicated on the display (see Section
9.3.3).
3.5.2 Computer Test
This is a method of automatic audiometry based on the Hughson and Westlake method and undertaken
automatically by the instrument. The level is increased in 5dB steps until a response is obtained from the
patient and decreased in 10 dB steps until no response occurs. The process is repeated until, depending upon
the criteria selected for recording a threshold (see Section 11.2.9), the instrument will record a threshold at
that particular frequency. The next test frequency is then used in the same way, and so on to complete the
test.
3.5.3 Bekesy Test
This is method of automatic audiometry devised by Von Bekesy (1947) using pure tone stimuli to track auditory
thresholds.
This application is known as discrete frequency Bekesy testing and the principle behind the test is that the
patient adjusts the presented level according to his hearing threshold. The decibel level decreases when the
patient presses the response switch upon hearing the presented tone. Conversely when the patient can no
longer hear the presented tone, he will release the response switch therefore allowing the level to increase
until the presented tone is heard again. The level changes are in 2.5dB steps.
When a number of these "peaks" and "valleys" have been consistently performed, the audiometer will calculate
an average to the nearest dB and display this as the hearing threshold at that particular frequency. The next
test frequency is then used in the same way, and so on to complete the test.
3.5.4 Single Frequency Test
The CA850 provides the facility to repeat an automatic test at a specified single frequency and add the results
into the overall audiogram result. This feature is useful for situations where one particular frequency has
proved problematic.
3.5.5 Mixed Test
This is typically used when one of the automatic tests has been unable to yield a threshold at one or more
frequencies. It is possible to use the alternative automatic test or a manual test (normally at just a few selected
frequencies) to complete an audiogram by adding thresholds to those already established automatically. The
resulting audiogram will be labelled as a ‘Mixed’ test.
