I'm getting ready to drill some holes in my boat this weekend! One of the multiple projects will be the addition of a pair of speakers, where previously there were none. I'm going into fiberglass, and am thinking of fabricating some plywood backing for mounting of the speakers. The area is not one that sees water.

Questions - What's the best way to mount the backing board to the backside of the fiberglass, an adhesive like 4200 or 5200? Should the plywood be prepped in anyway prior to install - that is sealed or painted?

Here's a pic of the install in a 'sister ship' that I'm flat out copying.



Thanks for the idea txjole!

Will your boat now have 6 speakers? If so, any changes to the stereo to accomodate?

I ordered my boat with the 'standard' stereo, not wanting to pay Four Winns an additional $1200 for $300 of equipment. So, it came with 4 middle of the road Clarion coax speakers (two in the bow, two in the cockpit) driven by a Clarion CMD4 4x60W Head unit. I'm adding a Clarion APX480M 4x80W amplifier, two higher end Clarion CMCX7.1 7" two-way coax speakers and a 10" Polk Audio MOMO Sub into the cockpit. I'll leave the Head unit's 60W/channel to the stock speakers, 80W/channel from the amp to the new 7" speakers, and a bridged 160W to the sub. The head unit/amp combo allows for non-faded inputs to the sub, and faded rear inputs to the two-ways, so I retain fading control between the two stock speakers in the bow, and 4 in the cockpit.

Should be a decent upgrade for about $225 in stereo components and about $105 in wiring components. I snagged some real deals on equipment for those that notice my math doesn't look right, retail would be closer to $600. I was going to go Polk Audio db650 for the new aft speakers, but the appearance was so much different from the existing white grilled Clarions, I backed off after buying a set. Probably should have just bought two more sets and replaced the four stock speakers too. Oh well, at least I'm leaving room for future upgrades.

So is the consensus that regular treated plywood mounted with 5200 is fine for bracing material for the coax installs?

Is the glass really thin? When I added mine the was no reason to add any type of backing. In fact the factory installed ones didnt have it either.

Backing is not a bad idea in my mind. Also, don't forget to put enclusres if you can to help with low end response.

I think 4200 would be sufficient. It's "removable" if you ever find the need to latter.

Did you compare the Clarion CMCX7.1 7" and Polk Audio db650 in store? I was debating between these two also. Same thing as you , the looks of the Polks are holding me back. To bad they don't offer white speaker covers.

You actually don't need much of anything to hold it in place. Make the screw holes in the fiberglass just a little oversized, hold the backer in place with a few dabs of silicone and tighten the speaker in place.

Don't use 5200 or it can't be undone. If the glass is very flimsy then use a backer but it probably is not necesary.

Use the 4200. Not a bad idea to use some sealer of some kind. Don't worry about what it looks like. An enclosure is a good idea. Drill the wood before putting any screws in it..Not oversize, but same size of screws or starter holes for them. It'll make screwing in the screws a little easier and less likely the screwdriver will slip and go thru either the speaker itself or your finger and blood gets... um... yea you get the idea..

After cutting the holes I found that Four Winns applied some type of coating to the back of the fiberglass. Check out the piece cutout below - the coating is very uneven, less than 1/2" on one side and just shy of 1 3/4" on the other side of a six inch cutout. This variance in thickness was enough to discourage me from installing backing board on the first go round. I might revisit this in the future.

Some kind of sound insulation to keep the echoes away maybe?

I think you will be happy with the results without an enclosure. Unless you're talking about subs, you only need the mounting face. The idea is to seperate the front wave from the back wave since they will tend to cancel each other out. Similarly, having too many speakers playing the same source can cause cancelations,(think "noise canceling headphones".

+1

As long as the face/finished surface is even and will flush up against the back of the speaker flange, with enough depth, mount those puppies up.

I wouldn't worry about the varied thickness behind. That backing material might help dampen rattles and standing waves (a good thing).

I don't see a need for any backing board, I'd tap directly into the fiberglass (masked and predrilled)

That's just what I did.