Contacta IL-CONTACTA-FSM Manual do utilizador - Página 5

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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.