One word to remember before reading any further: Ohms! Ohms
together with "+" and "" is what we need
to be aware of when connecting speakers. If you don't have your
Ohms right, then you might end up with a burned up amplifier.
Every speaker has ohms. The term is Nominal Impedance and the
unit is ohms. If you don't know the nominal impedance of your
speaker, look for something called Re. Re is the resistance
of the voice coil, and is close in value to the nominal impedance.
Another thing to remember is SERIES and PARALLEL.
Series connection
means we simply add each driver's impedance for a total impedance.
This is described as
Rtot = R1 + R2+......
A parallel
connection is a bit more tricky. the total impedance is described
as
1/Rtot=1/R1+1/R2+........
So, how
does one connect in series or parallel? Well, I will try to
explain by using examples and figures.
Example
1  Series connection of two 4 ohms speakers.
Let's say we have two subwoofers that have a nominal impedance
of 4 ohms each. For a series connection, the total impedance
would be 4 + 4 ohms = 8 ohms. The connection is done as
shown in the figure below. 

This
connection would give a final impedance of
8 ohms. 



Example
2  Parallel connection of two 4 ohms speakers.
For a parallel connection we would get a total of 2 ohms.
Mathematically speaking it would be 1/Rtot = 1/4+1/4;
1/Rtot = 0.5 which means Rtot = 1/0.5=2. To connect said
woofers in parallel: 

This
connection would give a final impedance of
2 ohms. 



Example
3  Series/Parallel connection of four 4 ohm speakers.
Let's say we have four woofers that each has
a nominal impedance of 4 ohms.
For a series connection, we would get 4+4+4+4=16 ohms.
Since most amps can handle down to 4 ohms bridged, a series
connection would be quite a waste of amplifier power.
In theory, you would get 4 times the power going from
16 to 4 ohms. And since we learned before that parallel
connections achieve lower impedance, let's see what happens
if we try to hook the four speakers up in another way.

Two series of 8 ohms each that
are parallel connected will yield a 4 ohm total impedance.
Mathematically speaking:
1/Rtot = 1/8+1/8; 1/Rtot=0.125+0.125; Rtot=1/0.25 =
4 ohms

This
connection would give a final impedance of
4 ohms. 



