I'm starting a project that involves playing an mp3 to an outdoor speaker, or speakers, based on a triggered event detected by an Arduino. I've already got an Arduino Uno and the mp3 shield from Sparkfun working properly and playing a file from the mini SD card. The next step, in my mind, would be to output the signal from the mp3 shield to some sort of amplifier to drive the outdoor speakers. This is where I'd like a little guidance. The ideal case would be where I don't need to have a consumer grade receiver/amplifier powered on all the time in case the event is triggered. Is there such a thing as an "instant on" amplifier that can be powered on rapidly by an Arduino "on demand"? I've seen amplifiers like the Kemo M034N 40W amp:http://www.parts-express.com/pe/showdetl.cfm?partnumber=320-554
and board amplifiers likehttp://www.parts-express.com/pe/showdetl.cfm?partnumber=320-330
but these don't seem like they are able to power a typical outdoor speaker like this: http://www.bestbuy.com/site/Insignia%22+-+Simulated+Rock+Outdoor+Speakers+%28Pair%29/8278124.p?id=1171058476697&skuId=8278124
For the board amplifiers, they strike me as needing to be continuously powered, not "instant on"... I suppose I could have an amp that is usually powered off, and then energize it with an appropriately sized transistor of some kind, but that strikes me as a major hack and not likely to work fast enough because of latency issues... Is the Kemo amp actually enough to drive a typical outdoor speaker?
Can anyone offer any suggestions or guidance?