4
Testing FM Systems with FONIX 6500-CX Analyzers
1: Coupler Measurements with FM Systems
Coupler measurements of FM systems allow you to adjust the system without needing your
client present. The goal is to set the FM system controls so that the user receives the FM sig-
nal at an appropriate level with reference to the acoustic signal the user receives from his
personal hearing aid.
There are four different sets of measurements described in this section. Use the set that is
appropriate for the FM system setup.
If the FM receiver and hearing aid are omni-directional and will fit inside the sound cham-
ber, and:
•
The FM receiver is primarily set to receive FM-only signals, follow the procedures
described in Section 1.2, Omni-directional: Testing FM-only.
•
The FM receiver is primarily set to receive FM with environmental signals
(FM+ENV), follow the procedures described in Section 1.3, Omni-directional: Testing
FM+ENV.
If the FM receiver or hearing aid is directional or cannot fit inside the sound chamber, and
•
The FM receiver is primarily set to receive FM-only signals, follow the procedures
described in Section 1.5, Directional: Testing FM-only.
•
The FM receiver is primarily set to receive FM with environmental signals
(FM+ENV), follow the procedures described in Section 1.6, Directional: Testing
FM+ENV.
For all procedures, the hearing aid should be set to user settings.
1.1 Coupler Setup in the sound chamber
This section describes how to attach a 2-cc coupler to the FM receiver, and how to set up an
FM system for coupler measurements.
1.1.1 How to Attach the 2-cc Coupler
A variety of output devices can be used with FM systems. These include button earphones,
BTE cases with microphone/earphones, BTE aids with an internal FM receiver, an external
FM receiver boot, or options for coupling to the personal BTE hearing aid via direct audio
inputs, silhouette coils, or neck loops. This section contains a description of how to arrange
the 2-cc coupler with each type of output device.