2.2
Installing a perimeter loop.
Where an induction loop facility is required to cover a room or defined
area, a perimeter loop should be used.
i) Loop Position and Size
The loop will often runs around the edge of the room and for best
performance should never be located at headheight (listening level). An
optimum spacing from loop to normal listening height is 12 - 16% of the
loop width. This often places the loop at floor or ceiling level. In special
circumstances, a range of 8 - 25% may be used, though the evenness of
the signal across the area is significantly degraded.
Alternative positions may be possible, such as covering the seated area
of a desk, etc. Contact Ampetronic for further advice.
The ILD20 is intended for use with loops up to 20m² in area. If the area
to be covered is larger, a more suitable driver unit should be used.
Please contact Ampetronic Ltd for details of other units available.
ii) Loop Cable
All Ampetronic loop drivers are designed to operate into
single turn
loops and must not be used with multi-turn loops.
The resistance of the loop should be between 0.2
W
and 1
W
. The cable
length limits for various wire sizes are as follows:
Cable size
Minimum
Maximum
section
length (m)
length (m)
0.5 mm²
5.5
28
0.75 mm²
8.5
42
1.00 mm²
11
56
1.8 mm² Flat Cable
20
87
Note 1
Note 1: value defined by maximum impedance at 1600 Hz, affecting
frequency response. Consult Ampetronic for further advice.
Normal stranded or solid-cored cable can be used. A suitable cable for
most applications is BS6231 ‘Tri-rated’ cable. Flat copper tape is
available for use under carpets where normal wire would be unsuitable.
3.
FITTING THE MICROPHONE
The selected microphone (tieclip, desktop or boundary) should be
positioned so that it is near to the desired sound source and directed
towards that source. There are many ways to mount the microphone
and the method used will depend on the circumstances of the
installation but should ensure that a clear, non-reverberant signal is
obtained.
Microphones must be the unbalanced electret type, suitable for
powering from the equipment. Balanced dynamic or condenser
microphones are not suitable for direct connection to the ILD20; if such
microphones must be used, the MAT60 adapter is available from
Ampetronic. The unbalanced microphone cable to the ILD20 should
never exceed 3m in length. Longer cables do not ensure that the EMC
immunity performance is maintained.
4.
INSTALLING THE ILD20 AMPLIFIER
The ILD20 should be positioned near to the loop coil in counter systems,
and may be placed in an enclosed space such as under a counter. It
may be mounted vertically or flat standing. For vertical mounting the
drilling template is provided with the equipment. Only use the specified
screws, and ensure that the unit is tightly held to the wall or surface
when installed. When mounted vertically, the microphone connections
are at the top.
The microphones, loop and AC power supply should be connected to
the appropriate terminals/connectors. Ensure that the loop terminals are
secure and that there are no trailing cables which might get caught or
pulled. Bunch up any loose cables and secure safely.
5.
SETTING UP THE ILD20 LOOP DRIVER
i) Turn the ‘DRIVE’ control to ¾ full. Set the ‘TONE’ control to mid
position.
ii) Increase the ‘MICROPHONE 1’ (or 2 if used) from minimum until the
green ‘Compression’ LED begins to light with normal speech from the
usual position of the counter staff, or with the normal input signal for
non-counter systems. The red ‘Current’ LED should light at peaks in the
input signal.
iii) Using a loop monitor receiver, adjust the ‘TONE’ control if necessary
for the best sound.
iv) If a field strength monitor is available, check the level at the listening
position and adjust the ‘DRIVE’ control as necessary.
Glass screen
(if fitted)
Place coil
immediately
below counter
Obstruction
Figure 2
Glass screen
(if fitted)
Counter
or
Desk
(customer side)
Counter
or
Desk
(customer side)
Place coil
immediately
below counter
Figure 1
Do not position
coil in this
position
