Tannoy VX 5.2 - Polarity Checking; Amplification and Power Handling

5. Polarity Checking
6
VX Series Operation Manual rev 1.1.2
5. Polarity Checking
Checking the polarity of the wiring before the speaker system is mounted or own will help ensure satisfactory
performance. If you do not have a pulse based polarity checker, you may check LF units as follows: Connect
two wires to the + and - terminals of a PP3 (9 V) battery. Apply the wire connected to the positive (+) terminal
of the battery to the speaker cable leg which you believe to be connected to pin 1+ of the speaker connector;
likewise connect the negative (-) terminal of the battery to pin 1-. If you have wired it correctly, the LF drive unit
will move forward. At this point, connect the positive (+) speaker lead to the + terminal on the amplier and the
negative (-) lead to the - terminal on the amplier. However, if the LF driver moves backwards with the battery
test, the input connections need to be inverted before connecting the amplier. If problems are encountered,
inspect the cable wiring. Note that different amplier manufacturers may utilise different pin congurations and
polarity conventions; if you are using ampliers from more than one manufacturer, check the polarity at the
ampliers as well as at the loudspeakers.
6. 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 overdriving the amplier into clipping. Damage to the loudspeaker will be
sustained if the amplier is driven into clipping for any extended period of time. Headroom of at least 3 dB
should be allowed.
When evaluating an amplier, 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 amplier running free of distortion will do less
damage to the loudspeaker than a lower power amplier that is continually clipping. A high-powered amplier
running at less than 90% of output power generally sounds superior to a lower power amplier running at
100%. An amplier with insufcient drive capability will not allow the full performance or the loudspeaker to be
realised. (See technical specications section for recommended amplier power.)
When using ampliers from different manufacturers in a single installation, make certain that all have very
closely matched gains. (Variation should be less than +/- 0.5 dB.) This precaution is important to the overall
system balance when only a single active crossover is being used with multiple cabinets. When possible, it is
recommended that the same ampliers be used throughout.