Contacta IL-CONTACTA-FSM, User Manual

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Measuring Frequency Response
Detailed below are two processes that can be used to confirm the
system properly reproduces all of the required frequencies equally in
the bandwidth of 100 to 5KHz. A Test Signal Generator such as the
Contacta TSG1 will be required to perform these tests. Both methods
will yield accurate results.
Method I - Sine wave signal
Send at a minimum the following sine wave signals through the hearing
loop system without adjusting any of the audio or loop level controls:
100Hz, 250 Hz, 500 Hz, 1000 Hz, 2500 Hz, and 5000 Hz. Using the Flat
Spectrum mode record the RMS level generated by each of these. To
meet the IEC specification the levels should not vary by any more than
±3dB.
Method II - Pink noise signal
Send a pink noise signal into the hearing loop system and select the
Third Octave mode on the meter. It will initially start at a 1000Hz center
frequency.
Pressing button “B” will cycle through the frequencies of 100Hz,
200Hz, 500Hz, 1000Hz, 2500Hz and 5000Hz.
IEC 60118-4 Notes and Requirements
The standard as revised notes that within the frequencies of 100Hz to
5000Hz the hearing loop system should equally reproduce all signals. At
a minimum the systems is to be tested at 100Hz, 1KHz and 5KHz.
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Program RMS/Peak Levels
The second mode is used to set up the hearing loop signal level using an
A-Weighted filter. It is very difficult to set the field strength to an average
of –12dBA as it will constantly vary based on the program used to set up
the system. We will use the PEAK read-ing to confirm that both our
design and equipment meet the IEC specification. Pressing button “B”
resets the PEAK reading.
How to test then adjust the loop system level:
Once the hearing loop system has been installed, play some bandwidth
limited (100Hz to 5KHz) pink noise or 1KHz sine (use the driver
manufacturers recommendation) though the loop system. Walk
throughout the audience area holding your meter vertically.
Note the readings and confirm that the A-RMS level does not vary by
more than ± 3dBA. This lets you know that the perceived signal level in
the hearing aids will be the same, no matter where the person is sitting.
Next: using program audio similar to what is normally used in the facility,
adjust the audio program level to a level just above “normal”. Now turn
on the hearing loop system and adjust the drive level until a –3dBA to
0dBA PEAK level is obtained in the center of the loop. Reset the PEAK
level and confirm this level averages 0 dBA across the audience listening
plane.
IEC 60118-4 Notes and Requirements
The revised standard states that the signal level across the loop area
should not vary by more than ±3dB. Once that is confirmed, the signal
level based on the building's normal program should peak at 0 dB as
referenced to a 400mA/m. This will confirm there is adequate loop
current to produce both the peak and average (average is -12dB or 100ma/
m) signal levels for T-Coil equipped hearing aids.