It's probably not exactly the answer you're seeking, but there's another viable option.
- You can pick up some nice automobile speakers, with water
resistant (plastic) innards/cones, & then make speaker boxes for them. And by that, I literally mean boxes, as in, out of wood. Much like is done for the Big speakers in high end systems in cars.
From there, you simply put a couple of electrical plug
connectors in a spot or three in the cockpit
, so that you can put the speakers where ever you desire. And needs be, you can put brackets in your cockpit
for them, with the other half of the mounting bracket on the speaker box. And or, put a couple of tiny pad eyes in the cockpit, to attach pieces of heavy bungee cord to, & use the bungee (or webbing staps if you like) to hold the speakers in position.
It's a KISS solution, that's worked for many decades. The only real catch being that it's wise to disconnect the speakers & stow them belowdecks when the weather
Though, the upside is that automobile speakers tend to have great sound quality, & are fairly inexpensive. Also, since the speakers aren't being exposed to the elements (water & UV) 24/7, they tend to last longer as well.
One other semi-Gucci perk to build into your boat's audio system, is to set things up so that you can have music
, but not down below (or vice versa). So that the off watch can sleep in peace, while the watch keeper/helmsman is rockin out, up on deck
You can do this with physical connectors for the speaker wiring
, or via the controls built into the stereo which let you select which speakers the music
is going to.