To make the most of your sound system, there are a few simple things you need to know. 

A little bit of knowledge will:

• Help you choose speakers that match your amplifier
• Teach you to connect speakers correctly
• Help avoid damage to amplifiers and speakers
• Make your system sound as good as possible

Impedence
This is the most important thing you need to know to set up your speakers correctly. Impedance is simply the amount of resistance a speaker has to a signal. The impedance of a loudspeaker cabinet is rated in ohms, and common ratings are 4, 8 and 16 ohms.

The impedanceof a loudspeaker is directly related to how much power it can draw from an amplifier. The lower the impedence, the more power it draws. For example, If you have an amplifier rated at 200W into 4 ohms, then a 4 ohm speaker will draw 200W of power from the amplifier. An 8 ohm speaker will draw only 100W from the same amplifier, while a 16 ohm speaker will only draw 50W. Now, some of you are thinking: "Cool - If I put a 2 ohm speaker on my 200W amp, I'll get 400W!" Unfortunately, if you do this the amp will try - and die in the effort. This also explains why, when you short the output of an amplifier, it has a tendency to blow. A short has virtually 0 ohms impedence, and the amp tries to provide an infinate power output.

The majority of amplifiers are 4 ohms and the majority of loudspeakers are 8 ohms. Remember that higher impedences are OK for an amp to handle (as they draw less power), so this is a perfectly acceptable situation, but you will only be using half of the available power of your amp. So how do you get the full power of your amp?

Impedanceis affected when you connect multiple loudspeakers together, There are two ways of doing this: in series and in parallel.

Series Connection of Loudspeakers
When you connect two or more loudspeakers together in series, the impedences are added together
(Impedance_Total = Impedance1+ Impedance2 + Impedance3, etc).

Parallel Connection of Loudspeakers
When you connect two or more loudspeakers together in parallel, the formula is a little more complex:

Which in the real world means:

So in the example of the four ohm amp, we can use 1 X 4 ohm speaker or 2 X 8 ohm speakers in parallel. We can also parallel two series pairs of 4 ohm speakers like this:

Each series pair gives us 8 ohms, and by paralleling the two pairs together we bring the impedance down to 4 ohms again. Clever, huh? An added benefit of this is that each speaker in an array like this handles only a quarter of the power of the amp, so using four 50W speakers gives you a combined power handling of 200W. But more on that next month, when we discuss speaker power handling.