simple speaker select switch request

Hi folks. I'm looking for a schematic for a 4-set speaker select switch. Basically, what I want to do is build a switch that would allow me to pipe my stereo to 4 different rooms or any combination. Can this be done with a mechanical switches or do I need a power supply? I'm an engineer (IT) but not very electronically proficient. Component recommendations would help too.

Thanks for the help!

Bucky

Just use mechanical switches but you might blow up your stereo amplifier.
Each set of speakers that are connected make the load on the amplifier closer to being a dead short. The amplifier has a minimum load impedance which is probably 4 ohms per channel. Two 8 ohm speakers connected make a load of 4 ohms. Four 8 ohm speakers make a load of 2 ohms which is too low.

Stereo shops have transformers that increase the impedance of speakers so more can be added to an amplifier. They are small so they reduce and distort the bass frequencies. Some have a volume control built in.

audioguru said:

Just use mechanical switches but you might blow up your stereo amplifier.
Each set of speakers that are connected make the load on the amplifier closer to being a dead short. The amplifier has a minimum load impedance which is probably 4 ohms per channel. Two 8 ohm speakers connected make a load of 4 ohms. Four 8 ohm speakers make a load of 2 ohms which is too low.

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The trick is NOT to put them in parallel, put them in series instead - that way things don't blow up, you just get less power out.

Hi Nigel,
I think speakers in series ruins the damping provided from the extremely low output impedance of an amplifier on the resonances of the speakers.

Experts say that only 1 ohm of wiring resistance in series with a speaker make audible changes in the sound. Another speaker is at least 7 ohms resistance and might have an impedance of 50 ohms at resonance. Two identical speakers in series would have no damping at their major resonance. Boom boxes.

audioguru said:

Hi Nigel,
I think speakers in series ruins the damping provided from the extremely low output impedance of an amplifier on the resonances of the speakers.

Experts say that only 1 ohm of wiring resistance in series with a speaker make audible changes in the sound. Another speaker is at least 7 ohms resistance and might have an impedance of 50 ohms at resonance. Two identical speakers in series would have no damping at their major resonance. Boom boxes.

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'Experts' often speak a load of rubbish! - I fully agree that putting speakers in series ruins the damping effect of the amplifier, but generally you can't hear any difference. Also, guitar and PA speakers are commonly wired in series/parallel, with no ill effects.

Better a poor damping factor than a dead amplifer! - and such speaker switching boxes are widely available in the shops.

Nigel Goodwin said:

I fully agree that putting speakers in series ruins the damping effect of the amplifier, but generally you can't hear any difference.

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Less expensive speakers are very boomy if they don't have good damping from the amplifier directly. They also "shriek" at their woofer's cone breakup frequency of about 5kHz without damping from the amplifier.

Try it. Tap the cone of a woofer without anything connected to it. It will "bong" like a drum. Then short its terminals to simulate the extremely low output impedance of an amplifier. When you tap its cone then it will have a well-damped "thump" sound.

Also, guitar and PA speakers are commonly wired in series/parallel, with no ill effects.

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Many guitar speaker enclosures have 4 speakers wired in series/parallel. They also don't have a back on the enclosure so the wild undamped resonance is "an effect".

audioguru said:

Try it. Tap the cone of a woofer without anything connected to it. It will "bong" like a drum. Then short its terminals to simulate the extremely low output impedance of an amplifier. When you tap its cone then it will have a well-damped "thump" sound.

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I generally play music through my speakers, I've never had an urge to use them as a drum?. I'm fully aware of what the damping effect is, and how it works - but it causes far less of a problem than you might believe - bear in mind the wires from the amplifier cause a big loss of damping factor as well!.

There are probably millions of speakers working in series throughout the world, if you haven't tried it don't knock it! - as I said, commercial units like this are freely available.

A transformer will provide more distortion than connecting two speakers in series.

If you really want to avoid the distortion associated with using a transformer then uprate it be a factor of 2 or if you want good bas then even 4. Core saturation is often the major factor as far as distortion is concerned.

High frequencies can also be a problem but you might be able to get around this by using a ferrite transformer with a suitable low frequency filtering capacitor to drive the tweeters.

schematic?

Riveting answers guys butback to the original request ... can anyone provide a schematic for what I need?