Just finished up a fun and easy project and thought I'd share. A little background: I've been riding most recently with a Jabra Street 2 http://www.amazon.com/Jabra-STREET2-Bluetooth-Stereo-Headset/dp/B005OW4AZK/ref=sr_1_1?s=wireless&ie=UTF8&qid=1353892223&sr=1-1&keywords=jabra+street2 around my neck connected to a set of earbuds; one of which I would have in, the other hanging down. I never got comfortable with the lack of situational awareness I immediately felt with both earbuds in. After perusing the various bluetooth options available for various helmets and a bit of sticker shock I decided to see what I could cook up with what I have around. Note- My reuirements for the build do NOT include phone usage while riding. I have no interest in this, but rather wanted a music/gps a2dp solution...
Parts: Jabra Street2, Sony MDR-027 cheapish headphones, 3m heavy duty velcro, zipties, electrical tape, and my HJC Symax2 helmet.
After removing the speakers from the headband assembly I added zipties to secure the line leaving the speaker against being pulled out and a little electrical tape to cover up the soldered connections.
Having added a small circle of velcro to the back of the speaker, and the receiving strip inside the helmet I wound up with the speakers sitting like this, fairly securely:
Now it was just a matter of routing the speaker cables behind the helmet liner and securing them with a few zipties, and adding the appropriate velcro to both the outside of the helmet and the back of the Jabra BT module. There you have it- In helmet wireless bluetooth audio that's also easily removable from the helmet, all for a total cost of around $70 depending on whether or not you have old headphones laying about that you don't mind trashing. Sounds great and really rather loud. Will report back after some road testing.