If your boat has 9 speakers, what else could you need... perhaps two more speakers for the radar arch.
Fact is, when we are up on the flybridge, the audio isn't as good as it should be, so the obvous solution is to add a couple of speakers to the arch. And since I have a tubluar arch, wakeboard-style speakers seems a good fit.
Limitations. Unfortunately, due to the construction of my radar arch, none of the speaker "cans" I was able to find would let me mount the speakers at level. I have to mount them at an angle. But that is OK, since the angle mounting provides a more direct path to the helm. I don't have an issue with the asthetics of this configuration, but if it looks out of place, the speakers could be mounted above the arch if desired, as well as many alternate locations.
I found some aluminum cans from Pyramid Manufacturing Inc., a small company that sells on eBay. For around $100, you get two cans made of spun aluminum, suitable for 6 1/2" speakers, and available in a wide range of tower clamp sizes, from 1 5/8" dia to 3" dia. While some manufacturers have adjustable clamps, this particular manufacturer's clamps are not. So make sure of the diameter.
An easy way to determine the diameter is to measure the circumference around the tubes, then use simple math and divide that number by Pi (3.14).
The cans come with binding posts, which I dislike. I tried to obtain cans that were undrilled, but they were not available.
So I retrofitted the cans by installing Heyco Cable Clamps in the rear hole, and Heyco blank fillers in the front hole.
I also sealed the rear fillers with 3M 5200 sealant to make them waterproof. The Heyco items are available from Mouser.Com.
Even though the speakers are outside of the canvas enclosure, the canvas is pretty transparent to the audio. The angle of the speakers means that audio can be heard from the aft deck as well.
At the helm, I placed the volume control for the arch amplifier, as well as the control switch for the source (Stereo or Cell phone Mic).
For more details, please review my Cellphone Communications system project.