Wow, so for $1 I could convert some old speakers to run off a USB power supply

I have a bunch of old 8ohm speakers that maybe seeing some new life soon.

http://www.instructables.com/id/Gift-Card-Tin-USB-Speaker-3-Build/

here is another build using a 15w amplifier (so $3 instead of $1)

http://www.instructables.com/id/Recycled-Old-Speaker/