Loc: Port Perry, Ontario, Canada
While my SpeakEasy is out for repair I decided to test my whole house audio speakers to make sure all is ready for Crystal's imminent return to duty (Crystal is our SpeakEasy's voice.)
I have 3 sets of stereo amplified PC speakers connected in parallel and located throughout the house so there are speakers in 6 different rooms. The output of the SpeakEasy connects directly to the inputs of these speakers.
To test the speakers I plugged the stereo jack that normally connects to the SpeakEasy to an MP3 player and voila, whole house music!
My question is this:
Could I have BOTH the SpeakEasy and my PC audio output connected in parallel to the same set of amplified speakers without causing any problems for either the SpeakEasy or the PC? I've done this many times before with regular audio equipment but I'm not sure what sort of load issues or back-feed problems this might create for the SpeakEasy?
I understand that the SpeakEasy would have to "speak over" the PC's music whenever it was playing but that would normally only be during the daytime when SpeakEasy messages are relatively infrequent anyway.
To solve that problem I could connect the PC audio through a relay and disable it using a Secu16 output before issuing a SpeakEasy message but it may not be worth the extra effort of wiring and programming for the odd occasion it would happen, If I did this I could use the N/C point for PC audio and N/O for the SpeakEasy - would breaking just the ground and leaving L & R connected work I wonder, guess some testing would be in order for that one!
You could try just making a passive mixer with resistors. Assuming that the signals are line level, you can try passing each source through a series 2.2k or 4.7k resistor, with the other end of each resistor connected together at the speaker input. Here is a page on passive and active mixers:
Yes, the resistors are there to prevent the outputs from "fighting" each other, possibly attenuating the signals or even damaging something (although this would be rare). A signal output is a bit like a power supply, putting out a varying voltage signal with a relatively low impedance. The series resistor increases the output impedance of each signal source, lessening the effect of the loading of one output by another. There is a bit of signal loss, but should be easily compensated by increasing the volume of the speakers slightly.
"If you don't know what you're doing, do it neatly..."