Series connection, one path
for current-impedance adds
Parallel connection, two
paths for current-impedance
reduces
Speaker Connections In Series Or Parallel
Oz Audio Vector Series Subwoofer User Manual
(5)
The diagram to the left shows two speakers connected in
series. Assume that the positive lead from the power
source connects to the left speaker's positive terminal,
and that the lead connecting over to the speaker on the
right also goes to that speaker's positive terminal. The
right speaker's remaining terminal is negative and is
connected to the negative terminal of the power
amplifier. Because there is one path for current that
passes through two impedances, the impedances add.
With these 2 ohm speakers, the resulting total
impedance would be 4 ohms. As the higher impedance
will reduce current flow for a given voltage, this
represents a lighter load to the amplifier than the single
speaker.
In the second example, the speakers are wired together
in parallel; there are two paths for current to flow. If the
speakers are the same impedance, then each will flow
the same amount of current, for twice the total amount
that the single speaker would otherwise flow (for a given
voltage). Therefore, if each speaker is 4 ohms, the
overall circuit impedance is 2 ohms. It should stand to
reason that a single 2 ohm speaker would flow the same
amount of current.
As you can see in the wiring examples how multiple
speakers are connected to an amplifier channel has a
great affect on the performance of the amplifier. If not
rated for a 1 ohm load, an amplifier connected to such a
load can over heat and shut down, or possibly even be
damaged. Also, an amplifier will not provide its best
sonic quality driving an impedance load heavier than it is
rated for.