Stereo to Mono Conversion for Multi-Room Audio

Do you want all the speakers to be playing at the same time, or only one of them? If it's the former, you can use clever series/parallel combinations of the speakers to bring the effective impedance down to 8 ohms. This is easy to do with 4 speakers, it might be doable with 8 speakers too. If it's the latter, I think you'll need to put in a selector box of some sort, so that only one speaker is connected to the amp's output at any given time. That will automatically take care of the impedance issue. You also want to make sure that your volume controls are rated for speaker level signals, and not line level signals. I'm not sure what in-wall volume controls are usually rated for.

BTW, if 2 speakers are in series, their impedances add up, if they are in parallel, the impedance gets halved (assuming identical speakers). So, if you do something like this:

Code:

   ----S----S----

__|              |__

  |              |

   ----S----S----

For the two speakers in each row, the impedance adds up.

So, if each speaker is R ohms, each of the rows is 2R ohms, and when you connect those rows in parallel, it goes back to being R ohms (half of 2R is R). 8 would be hard to do... 9 is doable again, use 3 rows with 3 speakers in each row.

That leaves the stereo to mono conversion. I know for a fact that you cannot do this by using a Y-connector in reverse. You'll need buffering... you could design and build a simple op-amp based circuit to do this, but I don't know if that's an option. Maybe there are commercial "summing" boxes available, I don't know. A subwoofer's input would do this, and you could hack into it to pull out the output after it gets summed, and before it gets low-pass filtered, but that's DIY again... sorry, no more ideas right now.

Hope that helps.