The EM Poll

Tech Basics Without Tears

Mar 14, 2008 5:29 PM, By Jon Chappell With Steve Oppenheimer

           

A PAIN-FREE EXPLANATION OF FIVE CONCEPTS ALL MUSICIANS SHOULD UNDERSTAND

Series

In a series setup, you merely add the impedances together. We know we said we'd keep the math to a minimum; this is easier than it looks. Let's assume we have an 8ž speaker and two 4ž speakers.

For a series setup, the equation is simple:
Z₁ + Z₂ + Z₃ = Z

So in our example (Fig. 1a):
8ž + 4ž + 4ž = 16ž

Thus, if we wire the speakers in series, our power amp will be dealing with a 16ž system.

Parallel

If we wire the speakers in parallel, and all three speakers have the same impedance, the formula is easy: the impedance of one speaker divided by the number of speakers. So if we had three 8ž speakers wired in parallel, the equation is 8ž ÷ 3 = 2.67ž. If our power amp can handle 2ž loads, that should work fine, but if the amp is looking for a 4ž load, this is going to make our amp work hard. With an amp designed for an 8ž load, this system is going to be bad news.

If the speakers are of varying impedances, things get more complicated. This looks scary but is easier than it appears:

In our three-speaker example (Fig. 1b), that gives us:

That will be ruinous for our amplifier; we can't do it.

Series Parallel

Calculating the impedance for a combination of series and parallel wiring is just a matter of applying each equation as needed. In our example, we can do this two different ways.

First, let's wire one 4ž and one 8ž speaker in series, then wire that combination in parallel with the other 4ž speaker (Fig. 1c):

The series: 4ž + 8ž = 12ž

Wiring our 12ž system in parallel with our other 4ž speaker gives us:

Let's see what happens if we wire our two 4ž speakers in series, and then wire that combination in parallel with the 8ž speaker (Fig. 1d).

First, we calculate the combined value of the series speakers:
4ž + 4ž = 8ž

Now, let's put that 8ž system in parallel with our 8ž speaker, which is simple, since we have two systems with the same value:
8ž ÷ 2 = 4ž

That should work perfectly.

One final tip: if you're in doubt, wiring in series always results in a greater impedance, and while it might be less efficient, it's the safest way to go.