Series Parallel wiring explained
If you want to drive two pairs of loudspeakers from the output of one amplier you can either
connect them to a switchbox or wire them directly. If you use a switchbox then you can have the
exibility of listening to either or both pairs as required. If you always want both pairs to be active
then it is possible to wire them directly as long as you are careful with the connections. There are
two ways to wire the loudspeakers; either in series or in parallel.
Wiring in series increases the impedance and will give a lower acoustical output. Wiring in Parallel
has the opposite eect of lowering the impedance and increasing acoustical output. When deciding
how best to connect have a look at the impedance of the loudspeakers you are using and also at
the specications for the amplier. Most ampliers will not work correctly with a load of below
4 ohms so if in doubt, always wire in series. These example use only two pairs of loudspeakers. It
is possible to combine more than 2 Speakers per channel. If connected in Parallel, (and assuming
each loudspeaker has the same impedance) then the net impedance of the load is equal to the
impedance of the one loudspeaker divided by the total number of loudspeakers.
For example 3 x 8 Ohm loudspeakers in parallel would equate to 8/3 (2.667) Ohms. If connected
in series (and assuming each loudspeaker has the same impedance) then the net impedance
of the load is equal to the impedance of the one loudspeaker multiplied by the total number of
loudspeakers, for example 3 x 8 Ohm loudspeakers in series would equate to 8x3 (24) Ohms.
A quick note about testing ceiling speakers.
It can be a temptation to take your newly purchased ceiling speakers out of the box and connect
them straight-away to see how they sound before tting them into place.
Be aware that all open back ceiling speakers will sound terrible if you simply connect them whilst
they are just sitting on a table. This is because they have been designed to be xed into a panel.
The panel (ceiling) acts as a
bae, and if there is no bae
then air can simply spill around
either side of the cone with next
to no resistance. This means the
front and rear waves are able to
cancel each other out, resulting
in a complete lack of bass and
a sound that is pretty awful. It is
not unknown for people to test
newly purchased speakers like
this and then send them straight
back to their supplier leaving
both parties somewhat disappointed.
If you want to have an idea of how they will sound before you mount them in place the simplest
solution is to use a couple of large cardboard boxes. Simply cut the appropriately sized hole in each
box, push the speakers into place and test them that way. They still won’t sound exactly the same
as they will in the ceiling, but the box will at least provide some semblance of a bae and give you a
much more realistic indication of their performance. If you don’t have any boxes then even mounting
them into large at sheets of card (or other material) will suce as long at the sheets extend at least
30cm from each edge of the speaker.
In fact a at sheet is what’s known as an open bae and in reality you’d need a sheet nearly 8m in
diameter to get a sub-50hz bass response! But the purpose of this is not to get into the ne detail
of loudspeaker enclosure design (fascinating a subject as that is), its simply to help you avoid any
disappointment before you nish your installation.
