FONIX® 8000 - Frye Electronics
FONIX® 8000 - Frye Electronics
FONIX® 8000 - Frye Electronics
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Chapter 6 125<br />
Coupler Directional Testing<br />
6.1 Introduction<br />
The Directional Polar and the Directional Difference screens are used with the<br />
FONIX 8120 Polar Plot Chamber to perform directional hearing aid testing, providing<br />
the hearing health clinician with a valuable tool used to verify that the<br />
hearing aid is providing a directional benefit and the nature of its directionality.<br />
The low-reflection design of the 8120 Polar Plot chamber and its automatic<br />
rotational features combined with the software in the Directional Polar and<br />
Directional Difference screens provide a clinical tool that was previously missing<br />
from the marketplace.<br />
Although the 8120 Polar Plot Chamber was designed to approximate laboratory<br />
testing results made in a large anaechoic chamber, there are some design considerations<br />
that make an exact replication of those results unlikely. Here are some<br />
things to keep in mind when examining directional measurements made in the<br />
Directional Polar and Directional Difference screens:<br />
• The speaker inside the sound chamber is very close to the aid being tested.<br />
In a large laboratory anaechoic chamber, the speaker will typically be a<br />
much larger distance away from the hearing aid.<br />
• The short distance between the hearing aid and the walls inside the 8120<br />
Polar Plot chamber do not allow the greater attenuation of reflected sound<br />
that is present in a large laboratory anaechoic chamber.<br />
• ITE hearing aids must be positioned in the 8120 Polar Plot Chamber with<br />
the faceplate perpendicular to the speaker. If a person were to be wearing<br />
an aid rotated in this manner, he would be rotated head over heels. This<br />
obviously isn’t desirable, but the 8120 Polar Plot Chamber would have to<br />
be considerable larger to accommodate a more realistic horizontal rotation.<br />
• The head shadow effect is not taken into consideration in Directional Polar<br />
and Directional Difference measurements.<br />
6.1.1 Features of the 8120 Polar Plot Chamber<br />
The 8120 Polar Plot Chamber is a desktop box that was designed to be small<br />
enough to be practical in a clinical environment but large enough to accommodate<br />
the special foam configuration (designed to minimize sound reflections) and<br />
the Rotating system used to mount and position the directional hearing aid for<br />
polar plot and difference testing.
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