When I built the speakers mentioned in the previous post, I had mobile use in mind, as well as just being able to transport them by bicycle. Last Saturday's naked bike ride was the prefect application, so I loaded up with a sealed lead acid battery (12Ah, although the 7Ah battery I have may have gone to distance too) and a smallish car booster amp (MacAudio MP2095 2x 50W). The speakers facing outwards in opposite directions gave me a great stereo effect; I've inevitably no real idea how the stero worked for others, but I do know that the music was appreciated by everyone who spoke to me, the quality (and volume!) often being commented upon. A great success, I feel, and even playing some Philip Glass worked well (as well as egyptian belly dancemusic, some folk rock instrumentals, then Banco de Gaia & the reggae version of 'Dark Side of the Moon').

Not actually 'bicycle powered', then, but a relevant use of kit I already had. Some technical details of the speakers:

Plywood boxes (12mm front & back, 18mm sides) 14x12x6", painted in blackboard paint

main drivers - Monacor SP-202E (10.3980) 8" dia 50W rms 4 Ohm - SPL 91dB. A compromise on size, price & efficiency - in these applications speaker efficiency, which can vary greatly, as does the useful audio volume.

Tweeters - cheap piezo horns, wired in with a series 80 Ohm resistor.

I made simple metal hook brackets to mount the speakers at an angle on the pannier frame (visible below), one side more or less following the line of the frame down tubes, to give plenty of foot clearance when cycling.

These gave loud, clear sound, coping well with bass. How loud everything went before distortion was nicely surprising, certainly more than loud enough to make a bit of a splash on central London streets. I must have been fairly noticeable as there's a picture of me on flickr, if you know where to look. ;-)

Addendum - one possibility for speakers of this size would be to include an amp and battery inside - not only making them self-conatined, but getting the weight physically ower (the battery would sit in the bottom). The battery and stereo amp could go in one side only, or a more balanced way would be to have small batteries in both sides, and mono amps. Most small car booster amps cam be bridged to a mono output, but one possibility for a mono amp would be the Kemo M034 amp module available from Maplin & elsewhere. I've got one to try - it claims a power supply of 6-16v, mac output of 40W into 4Ohms at 16v, 20W at 12v - that's likely to be enough, actually, for many applications. A bit of electronics to make a simple mixer, CD, gtr, mic inputs and you have a small completely paortable PA. It's a thought.