Audio Systems: speakers, dpdt switches, output impedance

Question
In my office I have two separate audio systems, each with its own speakers.  To save space, I would like to use just one set of speakers for both systems.  Can I simply connect an individual speaker to two different amplifiers?  Although I have no intention of running both amplifiers simultaneously, I'm wondering what happens if I forget and do exactly that.  Thanks for making your time available.
Bob

Answer
If you connect one speaker to two different amplifiers you are asking for a real tragic outcome; most likely it will cause failure of both amplifiers, but certainly one of them. The reason is it puts the two output connected together - which is a virtual short circuit.  Turning off the unused amplifier will not prevent it from being a short circuit to the live amp.  The output impedance of an amplifier is very low even when the power is off.  

A simple solution is to use a mechanical switch such that can connect the speaker to only one amp at a time.  You would need a DPDT (Double Pole Double Throw) toggle switch.  This would allow you to instantly switch the speaker from one amp to the other without the amps loading each other down.  You can find DPDT switches at any electronics parts store.  I think even Walmart has them in their electronics section. Radio Shack is a good place to find them as well.

Hope this helps.