Polo Boom-box Bike

I have also been looking up some amp stuff online; the t-series amp6/9s from 41hz...cost from 35-75 Euros depending.

Exactly what I had in mind. I bought one of the Lepei ones over the weekend, which is basically the amp6 made in a sweatshop and stuck in a metal case for £13. Music/testing starts as soon as it arrives :)

If they are 8 ohm, they a 5 parallel/2 series grid will reduce impedance to 3.2 ohm, which would help loudness without affecting the amp too much.

Awesome. And more parallel lines will bring the impedance down further too. The amp I have is fine with as low as 2ohm @12v. Cheap piezo horns for sure though. Ill add some of those to the shopping list. The only thing that sucks is cutting holes for 20+speakers..

For low-end, a couple of high-efficiency 8-12inch drivers would be necessary. I have seen some available for 30-60 quid each that look promising

If we're spending that much money though, why not just get better bass/mid drivers, drop the 20+ Wall of Speakers and just use the 10/12" speakers + piezo tweeters. No crossovers required. Did you check out the Bassinator link Mrak posted earlier that does exactly that?

I figure its Wall of Speakers for free vs Money for good speakers. BEsides, I'm not sure the trailer is big enough for 20+ mids + 2x12" bass + tweeters...

Regd. power supply. The car battery is available, but it will die with deep cycling (designed to be topped up almost constantly.) Since it is virtually new, I am a loath to kill it so quickly. And lug it across London for the privilege.

Yeah, lets not kill a new battery. Although using it for testing might be useful (if it wasnt for the lugging it across london part) The tclass amps use so little power anyway, so Scooter/smaller SLA batteries would be awesome. If we had any. A 7ah SLA is about £10-12, but we'd need two (or a bigger battery like the ones you suggested @£15-20). Itll still need plugging in to charge though. Alternately, a decent enough solar panel to keep this topped up is around £40, so that and a smaller battery works too.