FONIX® 8000 - Frye Electronics

76 FONIX 8000 Hearing Aid Test System
9. Position the hearing aid (with the Telewand held against it) for maximum output.
For BTE hearing aids, this usually occurs when the body of the aid is in
a vertical position. If necessary, use Fun Tak to help hold the aid in that position.
See Figure 3.4.10B.
10 Use [, ] to change the intensity of the magnetic field. The choices are:
OFF, 1.00, 1.78, 3.16, 5.62, 10.0, 17.8, 31.6, 56.2 and 100 mA/m. 31.6 is the
default source intensity.
11. Press [STOP] to stop the measurement or continue to test, as desired.
Figure 3.4.10B—Testing with the Telewand
3.4.11 Measuring directionality with the 8050 & 8060 Sound Chambers
Although directional hearing aids can have different types of polar plots and two
or even three microphones, the basic concept is fairly simple: speech sound from
in front of the hearing aid wearer is louder than noise from behind him. If you
have purchased the Coupler Directional Option including the 8120 Polar Plot
Sound Chamber and the Coupler Directional test screen, you can perform a polar
plot measurement of a directional hearing aid. See Chapter 6 for details. If you do
not have this option, however, you can still get a rough idea of directionality by
using the 8050 & 8060 Sound Chambers.
The directional test with the 8050 & 8060 Sound Chambers takes advantage of
the horizontal speaker placement and the flat testing surface that makes it easy to
position the hearing aid for testing. There are two measurements: one where the
hearing aid is positioned so that it is facing towards the sound chamber speaker,
and one where the hearing aid is positioned so that it is facing away from the
sound chamber speaker. You should use the same input signal for both measurements.
The source amplitude used for this measurement should be greater than
the noise floor of the testing environment, but less than the compression knee
point of the hearing aid, if possible. 50 dB SPL is usually a good choice.