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Public address installation
100V Line
When installing a 100V line system, it is
important that the correct size of cable is used to connect
the speakers to the amplifier. The following chart gives an
indication of what should be used:
| 100V Amp |
0.75mm˛ |
1.0mm˛ |
1.5mm˛ |
2.5mm˛ |
4.0mm˛ |
6.0mm˛ |
| 30W |
800m |
1066m |
1600m |
2666m |
4266m |
6400m |
| 60W |
400m |
533m |
800m |
1333m |
2133m |
3200m |
| 120W |
200m |
266m |
400m |
666m |
1066m |
1600m |
| 240W |
100m |
133m |
200m |
333m |
533m |
800m |
As the voltage on the line can approach 100
volts, installation must follow best practice with double
insulated cable being used. Cable runs should be kept away
from any potential source of interference such as 3 phase
mains, data, telecom cables etc.
100V line systems must always be wired in
parallel and the total load presented to the amplifier must
not exceed the rated output of the amplifier or damage can
result
100V line loudspeaker switching
In order to ensure that there is no
breakthrough it is necessary to use the circuit below when
switching 100 volt line loudspeakers either in groups or
individually. The loudspeaker is not only isolated from the
line but also shorted to itself in the "off" position thus
excluding any possibility of breakthrough.
100V Line Volume Controls
These controls are specially designed for
100V line operation and simply wired in-line (in series)
between the speaker and the amplifier. The maximum power
ratting of the volume control must be observed and not
exceeded, otherwise damage to both control and amplifier can
occur.
Low Impedance
Some amplifiers in the Adastra range have the
facility for connection of low impedance loudspeakers. Low
impedance installations require heavy cable feeding the
loudpseakers to minimise losses and short cable runs are
recommended. Where it is intended to use multiple low
impedance speakers to cover an aera, the speakers must be
wired in a series/parallel arangement in such a way as to
present the correct load to the amplifier.
Note: The total load
impedance presented to the amplifier must never be below the
rated amplifier impedance, otherwise damage can result. To
avoid damage to the speakers the total power of the driver
units should be at least 30% higher than the rated power of
the amplifier.
You must NEVER mix 100V line and low impedance
speakers on the same system.
Horn speakers are typically used in noisy
environments, outdoors or areas that are quite large in size.
The main disadvantage with this type of speaker is that they
cannot reproduce music at all.
General installation considerations
- DO NOT run microphone cables near mains, data,
telephone or 100V line cables
- DO NOT exceed 90% of the amplifiers output power when
using 100V line (speech only)
- DO NOT exceed 70% of the amplifiers output power when
using 100V line (high level background music only)
- DO NOT use re-entrant horn loudspeakers for background
music unless the loudspeaker has been specificatlly designed
for this purpose
- AVOID jointing the microphone
cable, when this is unavoidable make sure a good screened
connector is used, e.g. XLR
- ALWAYS use a balanced or
floating low impedance microphone terminating into a
balanced input on long microphone cable runs
- ENSURE that all loudspeakers
are in-phase
- ENSURE that there are no
short circuits on the loudspeaker line before connection to the
amplifier
Courtesy
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