AUDIOPHONY PUBLIC ADDRESS
Page 13
English
Note the readings and confirm that the A-RMS level does not vary by more than ± 3dBA. This
lets you know that the signal level perceived in hearing aids will be the same no matter where
the person is.
Next: Using an audio program similar to what is normally used in the building, adjust the level of
the audio program to just above "normal". Now turn on the loop system and adjust the player
level until a -3dBA to 0dBA level is obtained in the center of the loop. Reset the PEAK level and
confirm that this level is on average 0 dB in the people's listening device.
Notes and requirements of Standard 60118-4
The standard states that the signal level in the loop area should not vary by more than ± 3dB.
Once confirmed, the signal level from the normal building program should peak at 0 dB as
referenced at 400mA/m. This confirms that there is adequate loop current to produce both
maximum and average signal levels (average is de-12dB or 100ma/m) for hearing instruments
equipped with the T position.
The methods below are two processes that can be used to confirm that the system correctly
reproduces all required frequencies equitably in the 100 to 5KHz bandwidth. A signal tester
generator such as the BM-SCAN will be required to perform these tests. Both methods will give
precise results.
Send the following sinusoidal signals through the loop system without adjusting any of the audio
level or loop controls: 100Hz, 250 Hz, 500 Hz, 1000 Hz, 2500 Hz and 5000 Hz.
Using the flat mode, record the RMS level generated by each of these. To meet the specification
of the standard the levels shall not vary by ± 3 dB.
Send a pink noise signal into the magnetic loop system and select the third octave mode on the
meter. It will initially start at a center frequency of 1000 Hz.
Press button "B" to scroll through the frequencies 100Hz, 200Hz, 500Hz, 1000Hz, 2500 Hz and
5000 Hz.
6 - Frequency response
Field strength
Flat reaction
Third octaves
F = 1000 Hz
6-1 Method I - Sinusoidal signal
6-2 Method II - Pink noise signal
FS-RMS :
-12.5 dB
MAX :
-10.2
