I recently tried to tackle this question for my recent theater production.

I use a very basic 30-watt(max) home-stereo amplifier to drive a 1980's vintage pair of Kenwood speakers, three-elements, the woofer being 10". This sounded fine for years, just for music and sound effects.

When we added stage mics, I quickly realized that these speakers didn't push the mic sound to the back of the audience, without feedback, of course. So I picked up a pair of 8" bookshelf speakers, and hung them about half-way in the room, where our average audience back row would be. Wired in parallel. It works fine, sounds OK, the mic levels still can't go as high as I'd like.

This last show had one actress that couldn't even project (with British accent) to the first row. Even listening in the headphones, I had a hard time hearing her. My stage manager, had a set of DJ-size speakers and a 200 watt amp. My home-stereo amp had been fed by the tape-out on the mixer, so I still had the standard line-out available. I fed the big amp with the line-out. And mounted the Kenwoods in the rear instead of the bookshelf speakers.

STUPID us, we did this on opening night, and failed to try it out with complete silence... as the curtain went up and we were greeted by a very noticeable hum. A hum so bad, that the reviewer moved to the back row (where the hum wasn't noticeable, because the speakers back there were fed from the home-stereo amp) at which point he couldn't hear the actress very well. As I frantically tried everything on the mixer, I finally cut the amp, and the hum went away. It was so bad I had to buy my producer an extra drink after the show to make up for it.

After the show (and drinks) he and I stayed late and fiddled with everything. No matter what, the amp seemed to be the culprit. We tried the church's powered mixer, and then all we heard was a loud static. Then we also tried the church's speakers, and the static was less pronounced. (difference in speaker construction - plastic vs wood/carpet) I even tried breaking the ground-path, which only solved a hum coming from my computer. (which my producer never complained about until now, even though I knew was there all along) Finally, I adapted my red/black pin speaker wire to 1/4" and fed the speakers directly with my little amp. No hum, the static was barely perceptible from 5 feet. Music sounded fine, and the stage mics could be heard very well, without being turned up to feedback. The home-stereo amp was still only turned up to half-dial.

We ran like this for the rest of the performances, and I got compliments from a number of people on the sound.

I was totally surprised by this.. and I'm not sure why. I thought that PA-level speakers wouldn't work with home-stereo-level amps... not enough voltage or something. So now I was running both speakers in parallel, both specified to be 8 ohm loads, so I know that overall, each channel is still representing 4 ohms to the amp, just as before, only the speakers involved are larger.

Rob Cashman
Customer Support Engineer