I have an old stereo amp that I am using for my TV sound system. I have my "A" channel into a set of Polk M20's. I also have my "B" channel into a set of passive subs. It sounds good, but I want to add a third set of speaks. Since I do not want to drop below 8 ohms, I have an issue. I have added the third set of speaks in series with the subs, and it is weak as hell being 16 ohms. Is it possible to hook two speakers up in series/parallel? If I run the + out of the amp into the + on the speaker, the - out of the speaker into the + of the sub, and the - out of the sub into the amp, I get series. Can I keep that, but run two more wires from speaker + and -, into the + and - of the sub? Will that blow the amp to pieces, or will it result in an 8 ohm resistance? Please help.

Don

I run the + out of the amp into the + on the speaker, the - out of the speaker into the + of the sub, and the - out of the sub into the amp, I get series. Can I keep that, but run two more wires from speaker + and -, into the + and - of the sub? .
Don

Any two speakers can only be connected in one or the other configuration; series or parallel.

If you connect 3 spkrs on each side you get more choices by using a serries/parallel combination. Two in serries to get 16 ohms and connect that pair in parallel with the third.

1/Rt =1/16 + 1/8
1/Rt = 3/16
Rt = 5.3 ohms

If your speakers are all of different design it is possible that the individual impedance curves will combine at some frequencies to either greatly raise or lower the momentary impedance. So if you try this go easy on the gain at first.

Or you can buy or make an impedance matching speaker switch designed to work with amps that cannot drive low impedance loads. :)

So there isn't a way to have two 8 ohm speakers running off the same channel to stay at 8 ohms? Thats a bummer.

Don

If you had four 8 ohm speakers you could get it down to 8 ohm.

So there isn't a way to have two 8 ohm speakers running off the same channel to stay at 8 ohms? Thats a bummer.

Don

Are you certain that your amp won't drive a reduced impedance? Many units will handle 5 ohms without over heating.

If it just won't do it you can put a heavy duty resistor, like this $.69, 8 ohm 20 watt wire wound from Parts Express in place of a fourth speaker.
http://www.partsexpress.com/images/017-027m.jpg
That would give you [two speakers in parallel for 4 ohms] connected in series with [one speaker and the resistor in parallel for 4 ohms].

Trekguy: Would it? Are speaker ohms measured as impedances or resistances?

I have my "A" channel into a set of Polk M20's. I also have my "B" channel into a set of passive subs. ...............I do not want to drop below 8 ohms,...............
Unless the "A" and "B" channels represent 4 separate amps instead of 2 (1 right, 1 left), you're already below 8 Ohms.

Unless the "A" and "B" channels represent 4 separate amps instead of 2 (1 right, 1 left), you're already below 8 Ohms.


I agree. Most A/B setups are just one channel (amp) with each speaker running parallel. Assuming the Polks and the sub are 8 Ohm, you're already at 4 Ohm nominal now. I would advise against using a resistor because 1) it must be rated for the highest power teh speakers could see, 2) it'll just be sink for the amp, 3) it'll get hot as hell, 4) it's just not a good solution.

You're asking too much from that amp. You need to decide what your needs are and buy amplification according to that.