Wiring - A quick lesson in Physics.

A simple way to get more power out of amplifiers is to wire speakers in different ways, playing with resistances to achieve a desired total impedance as "seen" by the amplifier. Even though speakers are active loads i.e. resistance changes with frequency, it is accepted to consider speakers as resistors with a fixed resistance value (usually 4 ohms). By combining speakers in different ways, maximum amplifier output can be obtained.

Parallel Resistance

People commonly connect two or more speakers to the same channel out of an amplifier in parallel. This is achieved by connecting the negative wire from the amplifier to all the negative connections of the speakers, and the positive to all the positive connections of the speakers. By doing this, the load seen by the amplifier is lower. For example, if two 4-ohm speakers are wired-up in parallel, then their total resistance will be half, or 2 ohms. If three speakers are wired up in parallel, and they all have the same resistance value, then the total load would be a third of the value of each speaker's resistance. Here's a formula to calculate parallel total resistance for two speakers:

For more than two speakers, use the following formula:

One plus on using this is that if one of the speakers burns out, then the other one(s) keep playing. If the amplifier however is not designed to receive lower loads provided by connecting the speakers up in this fashion, you might end up destroying your amplifier. Check your manual or consult an expert before experimenting.

Series Resistance

Speakers that are connected in series, decrease total load to an amplifier. To connect speakers in series, connect the positive terminal of the amplifier to the positive of one speaker, then hook up negative of that speaker to positive of next speaker, and so on. Then connect the negative of last speaker to negative of the amplifier. It is a lot easier to calculate total resistance for speakers connected in series. This is easily done by adding up all the individual resistances as seen in the formula below:

other than getting less power out of an amplifier, if one of the speakers burns up, the other one(s) stop working thus this is not a preferred choice when connecting subs.

Drawings courtesy A' Level Physics - Burt & Lancaster