relationship between ohms and # of speakers?? (1 Viewer)

[Benny G]

Can someone please explain the relationship (if there even is one!) between ohms and the # of speakers powered by an amp?? Thanks in advance.

 

[Vince Maskeeper]

Benny,

Somewhat complex question, but I'll do my best to answer it.

There are two ways to wire speakers, Parallel and Series.

When you wire Parallel the impedance number gets lower. So, if you have two 8 ohm speakers wired in parallel and feeding off the same amplifier channel- that amplifier channel sees it as a 4 ohm load. The more speakers you add in this method, the lower the impedance and the bigger the load you place on your amplifier. Most amplifiers have very strict limits on what kind of load they will handle before they, well, burst into flames.

Wiring in parallel means you wire from the amp + and - to the first speaker's + and -, and then from the first speaker's + and - to the second speaker's + and -, etc.

When you wire in Series, the impedance number gets bigger. So, if you take two 8 ohm speakers wired in series and feeding off the same amplifier channel- that amplifier channel sees it as a 16 ohm load. The more speakers you add using this method, the higher the impedance and the less wattage gets to the speakers (and series wiring can also effect the quality of the signal).

A series connection is a little more complicated. First, you connect the "+" terminal of the amp to the "+" terminal on the first speaker. The next thing you do is connect the "-" terminal of this first speaker to the "+" terminal of the next speaker speaker. Continue doing this until you run out of speakers, then you connect the "-" terminal of the last speaker to the "-" terminal of the amp. You can see in this connection that power from the amp goes through both speakers one after the other, hence the name "series."


If you're looking to run multiple speakers- your best bet is usually to run each off its own amplifier channel, This will yield the best performance and the safest operation.

If you absolutely must have several speakers feeding off one amplifier channel, it's best to mix the two wiring methods to achieve a finished impedance matching the ideal levels for the amplifier. So for example, you could have a two sets of 8 ohm speakers wired in series giving you a 16 ohm load, and wire those sets together in parallel to get you back to 8 ohms.

-V

 

[Benny G]

Thanks Vince. You answered the question very clearly!

 

[Wayne A. Pflughaupt]

If you absolutely must have several speakers feeding off one amplifier channel, it's best to mix the two wiring methods to achieve a finished impedance matching the ideal levels for the amplifier. So for example, you could have a two sets of 8 ohm speakers wired in series giving you a 16 ohm load, and wire those sets together in parallel to get you back to 8 ohms.

It probably should be added that there is “no free lunch,” as it were. While a series/parallel combination like Vince described will result in the amp seeing a favorable impedance, that doesn’t necessarily mean “all is well.”

For instance, if it took only 15 watts to drive one of the speakers to your normal listening level, the amp will theoretically be pumping out 60 watts to drive all four speakers at the same level.

So any way you cut it, your amp is always working harder driving multiple speakers. That’s why it’s best (for the sake of reliability) to keep a single speaker per amp channel, as Vince recommended.

Regards,
Wayne A. Pflughaupt

 

[Bill Lucas]

`Benny,

An easier method than the one described by Vince is to use a impedance matching speaker selector. Hook the amp up to the speaker selector and then wire normally to the speakers you wish to use. A benefit is that a speaker selector has switches to turn individual pairs on or off at will. Regards.

 

[ThomasL]

I use a Niles speaker selector (~$100) and like the one I have, they'll typically either have a switch that introduces a resistor into the equation so the amp never sees a load below 4 ohms. I believe the Niles has a 2.5 ohm resistor so if you have 4 pairs of 8ohm speakers then, in theory, the receiver should see a load of 4.5 ohms if my math is correct ((8 / 4) + 2.5). I typically only switch on the protective circuit if I try to drive all 3 bookshelf pairs I have hooked up to it. Other speaker selector models use an automatic protection circuitry setup where it'll turn on itself if it sense the load is getting dangerous. Usually these models have a single speaker pair set that do not go through the circuitry. This would be for your main listening speakers. I tried one of these models from Acoustic Research and it didn't work so I become suspicious of these automatic models and went with one where I could control whether or not the added resistance is put into the equation.

cheers,


--tom