As you can see from the diagram, the
speakers go into the amplifier and the amplifier goes into the main outputs of
the mixing desk. The speakers connect to the corresponding left and right
inputs on the amplifier via speaker cables (blue wire), and then returned to
the mixing desks left and right outputs via XLR cables (red wire). This is very
simple set up, and the only thing to consider is getting the left and right speakers
the correct way round, and by this, I mean connecting the left speaker to the
left input, then taking that input to the left output of the desk, and doing
the same with the right speaker. If there is a mix up in the routing then you
could potentially have them the wrong way round which would make panning any
audio go to the wrong speaker. It is very simple to reverse though, just swap
the cables around.
Wattage and resistance
The next thing to consider when
using speakers in a live sound environment is the wattage of the speakers and
amps, as well as the resistance. The wattage of things is measured in watts (w
for short) and wattage is basically the amount of electrical potential that
something has. Using guitar amplifiers as an example, a 15 watt amp has less
potential energy than say a 50 watt amp, meaning that a 50 watt amp can go much
louder. In regards to speakers and amps, it works in very much the same way
that the higher the wattage they both have, the more potential volume you can
get out of the speaker. You have to be careful with speakers and amps though, because
say you have an 800 watt amp and two 500 watt speakers, you would not be able
to power the speakers because the amp wouldn’t have enough power. Two 500 watt
speakers equals a kilowatt, and the amp doesn’t have a kilowatt of power, so
you either need to get a bigger amp with at least 1000 watt of power, just use
one 500 watt speaker or get two speakers that equal less than 1000 watt of
power. It is best to balance the signal, although leaving about 100-200 watt headroom
between the amp and speakers would be beneficial. Having an amp too small for
the speakers wouldn’t be enough to power the speakers as I have just mentioned,
but having an amp too big for speakers also wouldn’t be good either, simply
because running too much power into small speakers leaves the risk of blowing
the speakers and ruining them, hence why it is best to balance the signal.
Resistance plays a key part in
everything because it determines how loud you can actually get your speakers.
The resistance of an amplifier can vary, although they are usually around 8
ohms, ohms being the measurement of impedance (resistance). The impedance of an
amplifier is relevant to the wattage and impedance of the speakers, because say
for example you have two speakers at 200 watts, 8 ohms, you will be demanding 4
ohm and 400 watt out of your amplifier, whilst still feeding 200 watt in each
speaker. This may sound confusing; however it is very simple once you know the
formula. This diagram below will show you exactly how it works: