Step 2: Efficient speakers
Large speakers (both boxes and driver cone size) are nearly always more efficient than small ones. If you don't care so much about the weight get the biggest speakers (15" or larger woofers). If you do care, the weight and size of the speaker will be your main tradeoff in your setup
Think about going MONO! Stereo doesn't always make a lot of sense in an informal environment. Using one larger speaker you will have overall higher efficiency and lower weight than two smaller ones.
I built and tested systems using the speakers listed below. All but the smallest are rated SPL between 95 and 98:
- Behringer S1020 - 10" woofer, 20 lbs, $100
- Behringer B212XL - 12" woofer, 25 lbs, $170
- Pyle PPHP121 - 12" woofer, 30 lbs, $120
- Peavey PR12N - 12" woofer, 25 lbs, $180
- Peavey PR15N - 15" woofer, 32 lbs, $220
- Gemini RS-308 - 8" woofer, 15 lbs, $70
Our tested results for these speakers: The Peavey and Pyle are the loudest with the same power input, and about equal to each other. The Behringer's are noticeably less loud. The B212XL and the Yamaha have noticeably better audio quality than the others. (more results later). The Gemini is by far the smallest speaker here - it will fit into a milk crate - its not as loud as the bigger ones but great for its size.
Bigger speakers (15" or 18" woofer) can get up to 100 or 101 SPL efficiency. With more expensive speakers you can find something a little more efficient, but mostly you are buying higher sound quality and a higher maximum power level. Running off batteries you likely will be well below the maximum power levels.
Where to find this stuff:
and others... (amazon.com has some of them)