To also answer, not only ask. I also have been curious about Bluetooth speakers, since I travel a lot, do a lot of hiking/camping, and a good audio with battery that can charge up the phone, when you dont have a electric socket anywhere near really sold me at that point. Since it was about 3+ years ago, there wasnt much to choose from, this was a beginning new trend. So i bought one, that I could actually get my hand on before, and listen to, it was amazing, for a portable speaker of course, so those little speakers connected together with some bluetooth board and a battery can really cheer a group up, when you are miles away from civilization.
This one was from the bit pricier range, but it traveled half of the world with me, and it still works as a charm.
http://www.usa.philips.com/c-p/P8BLK_37/fidelio-wireless-portable-speaker
Good luck with DIY project, it will certainly be interesting to do something like homemade bluetooth speaker.