Sub box material?

[Beach-TJ]

I'm planning to install a sub in my boat this winter and I have been thinking about what material to build the box out of. I'm think I am going to mount the sub under the drivers console. I installed a heater last winter, so I have some idea of the space and what I am getting into there. I have both a 10" and 12" sitting in the closet, so I will use the sub that fits the amount of space I can come up with.

I have built several boxes for cars and Jeeps using MDF, so I'm familiar with that. I know MDF works well acoustically, and is easy to work with, but doesn't mix well with water. I have sealed MDF boxes to use them in Jeeps and make them resistant to water, but I'm not sure how well that would hold up in my boat. Is sealing MDF good enough?

I know that fibreglass works well acoustically, but it's a PITA to work with and I'm not sure I want to go down that road.

I also know that marine plywood, if thick enough, works well, but it's almost impossible to source. Anyone know where to get some in the Atlanta area?

So, I was look at materials like these Starboard poly sheets. I have used them for some other projects, there a little pricey, but easy to work with and water isn't an issue with them. I'm wondering, how do they perform acoustically?

I would love to hear any advice on what materials to use to build a sub box for the boat.

Thanks,
Bryan

[core-rider]

I'm running MDP that I covered with a layer of fiberglass mat and resin, then covered in carpet. Been running strong for a few years now with no signs of swelling. It sits right behinf the driver's seat in the floor of my 03 SANTE so you know it gets wet from time to time.

[TxJole]

Birch then rhino lined, or starboard go to bed bath and beyond and get a huge cutting board. Same stuff only cheaper. Or Ace Mart resturant supply if u have one local.

[EarmarkMarine]

KingStarboard is not going to work because you will not be able to have a lasting bond at the seams.

MDF is acoustically inert but is constructed with water soluable adhesives. You can coat it with polyester fiberglass resin which is still micro-porous. Epoxy resin is better. And poyurethane bed liner works very well.
Any of the above options are okay but execution has to be perfect for the enclosure to last. All seams plus staple or air nail impressions must be completely filled and sanded smooth. Radius all corners as coatings tend to thin and shrink from hard edges. The coating is only as good as the mix. Too hot and its brittle. The key is to elevate the enclosure off the sole with HDPE or other polymer risers so that the enclosure won't eventually wick up moisture through the coating. You have to build in drainage and evaporation. Besides, if you place an enclosure bottom directly on a carpeted sole not only will any enclosure fail but you are creating a moisture trap and inviting mold and mildew.
MDO and Medex are just two of the many solvent based exterior grade materials. Used for exterior signage and road signs for decades with lasting results. But they were elevated and drained. This is an improvement over MDF but whether using a plywood or fiberboard, MDF or MDO, I would still coat it and elevate it. Again, the execution in making a precise enclosure with no inroads for water plus elevation are the keys.
And, use a high quality binding post terminal cup if you want the enclosure to stay sealed.

David
Earmark Marine

[Beach-TJ]

Thanks Jason and Jole, its good to know that coated wood can hold up.

Thanks for the detailed response David, as usual it is very helpful.

Its looking like MDF may be the way to go, just with some extra work to protect it.

[xrichard]

FWIW, if you are comfortable with marine plywood, then you'll be fine using exterior grade plywood....they use the same glue, but marine ply is supposed to be entirely void free. Marine grade ply otherwise does not have any special waterproof qualities. If you use any wood, it's best to elevate the box off the carpet. Keeping it from getting wet is your best bet.

[jllogan]

fiberglass isnt that hard to work with especially if you are coating something. I have seen alot of guys use fleece as well instead of cloth and then coat with resin. Epoxy resin is the best as it is waterproof and not hard to work with IMO. You could make a wood frame of any wood then coat with a tinted resin for waterproofing, I would avoid carpet as it retains moisture and will not dry out fast out of the sun.