Electronics Expert question?

[HeairBear]

Why do you want to do this? Why not just use two separate speakers? What kind of equipment are you working with?

[the_big_m_in_ok]

...I am trying to hook up two devices to one speaker and I dont want to get bleedoff back into the other system, how do I do this?

http://www.allaboutcircuits.com/vol_2/chpt_9/3.html

In the first page example, DC is isolated from AC on the left side.  You might wire two 1:1 transformers as series on the input and parallel on the output?  Otherwise an RF mixer could be used?

http://www.tkk.fi/Misc/Electronics/circuits/linemixer.html

Please keep in mind these are suggestions to an unusual question in a sub-discipline of electronics (audio/sound engineering) that I'm not very familiar with. 
Wait, the transformer would contribute BEMF/CEMF to the circuit through both coils by core induction, right?  Voltage spikes can ring back to the AC/audio source.  However, at a 1:1 coil turns ratio, the spikes wouldn't be very big.  Whether or not this is objectionable to Dr, is something he'll have to determine.

I think the mixer might work better, though.

--Lee

[Thedane]

Why not simply use a relay?

http://en.wikipedia.org/wiki/Relay
- look up DPDT (DPDT â€" Double Pole Double Throw)

Simple and cheap. 

//Egon

[Dr]

@ All: Thank you for all the great replys, What I am attempting to do is  use one of the speakers I already have in the ceiling (100) watts, for an intercom system also, so it would do double duty, but I dont want the intercom blasting through the rest of the system, when I am listening to music or watching a movie, I didnt want to add another speaker , because that would mean tearing open the walls that have just been finished. So I think I need something that I can put between the wires and the speaker.  yes? no? 

[HeairBear]

Yes, it is doable. The solution is simple, but you will need a bit of rewiring and some sort of switch. That one speaker can be connected to both the sound system and the intercom system. The switch will be used as an A/B. A being the sound system, B the intercom. I would imagine the switch being close to the intercom. How that switch is activated could be as easy as a manual switch to something more complex like automatic switching activated by the intercom system in some creative way.