6
CABLE RUN
(m)
C.S.A. OF EACH
CONDUCTOR (mm)
CABLE
RESISTANCE
Ω
Ω
% POWER LOSS
INTO 8
Ω
Ω
LOAD
% POWER LOSS
INTO 4
Ω
Ω
LOAD
10
2.5
4.0
6.0
0.14
0.09
0.06
1.7
1.1
0.73
3.5
2.2
1.5
25
2.5
4.0
6.0
0.35
0.22
0.14
4.3
2.7
1.8
8.6
5.4
3.6
50
2.5
4.0
6.0
0.69
0.43
0.29
8.6
5.4
3.6
17.0
11.0
7.2
100
2.5
4.0
6.0
1.38
0.86
0.58
17.0
11.0
7.2
35.0
22.0
14.0
4. Polarity Checking
It is most important to check the polarity of the wiring. A simple method of doing this
without a pulse based polarity checker for LF units is as follows: Connect two wires to
the +
ve
and -
ve
terminals of a PP3 battery. Apply the wire which is connected to the +
ve
terminal of the battery to the speaker cable leg which you believe to be connected to
Pin 1+ of the speaker connector and likewise the -
ve
leg of the battery to Pin 1-.
If you have wired it correctly the LF drive unit will move forward, indicating the wiring is
correct. All that remains now is to connect the +
ve
speaker lead to the +
ve
terminal on
the amplifier and the -
ve
lead to the -
ve
terminal on the amplifier. If however the LF
driver moves backwards, the input connections need to be inverted.
If problems are encountered, inspect the cable wiring in the first instance. It should
also be noted that different amplifier manufacturers utilise different pin configurations
and polarity conventions. If you are using amplifiers from more than one
manufacturer, check the polarity at the amplifiers as well as the loudspeakers.
5. Amplification & Power Handling
As with all professional loudspeaker systems, the power handling is a function of
voice coil thermal capacity. Care should be taken to avoid running the amplifier into
clip (clipping is the end result of overdriving any amplifier). Damage to the
loudspeaker will be sustained if the amplifier is driven into clip for any extended period
of time. Headroom of at least 3dB should be allowed. When evaluating an amplifier, it
is important to take into account its behaviour under low impedance load conditions. A
loudspeaker system is highly reactive and with transient signals it can require more
current than the nominal impedance would indicate.
Generally a higher power amplifier running free of distortion will do less damage to the
loudspeaker than a lower power amplifier continually clipping. It is also worth
remembering that a high powered amplifier running at less than 90% of output power
generally sounds a lot better than a lower power amplifier running at 100%. An
amplifier with insufficient drive capability will not allow the full performance of the
loudspeaker to be realised.
It is important when using different manufacturers amplifiers in a single installation
that they have very closely matched gains, the variation should be less than +/- 0.5dB.
This precaution is important to the overall system balance when only a single
compressor/limiter or active crossover is being used with multiple cabinets; it is
therefore recommended that the same amplifiers be used throughout.
