This is a mount I made to hold a "CANZ" bluetooth speaker to the underside of my windscreen.

The speaker can be found at Walmart, I got extreme hold 3M double sided tape at Thisens, along with a short nylon strap, the only other thing needed is a pad to wrap around the speaker to make a snug fit. I used a non-slip dash pad that usually holds a cell phone on your car, but you could use something else like a mouse pad I'm sure.

It works great and sounds awesome, it does get a little harder to hear over about 45 mph but that's just wind noise.