Public address installation guidelines
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
rating 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
cannont 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 ot the
amplifie
Courtesy of
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