Phragle....

Two 4 ohm 10's in parallel will give you 2ohms terminal load. You will net roughly 120 watts each. That's not a lot so bass and box is everything. Look at the fs number on your sub. It is on the sheet in the box they came in under thiele small parameters. This number will tell you the "resonant frequency" of the sub, and you can design you box around this. Many free online programs will assist you with this. I use term lab, but that's an expensive way to get it right.

A good custom audio shop will have term pro, bass box designer, pro box......

I also recommend no two parallel sides in your box. Parallel sided boxes allow the rear frequencies to cancel eachother out reducing your output.

Because subs play lower, the wavelength takes longer to develop. To help facilitate "loading", it is best to build a box that is vented to the rear and combines with the front in the loading chamber....then vented beyond the box to the listener. This reduces band width, but amplified output within that bandwidth.

This is called band pass. Higher output in a narrow field with less power needed. Plus, you cannot hear distortion from the sub. Bad news is you have to control the sub within the intended range or it will eat itself.

You can find several different designs on line (2nd, 3rd, 4th order)

You could also buy one from a car audio shop prebuilt based on their recommendations knowing which combos they have had success with.

Then, you can go home, rip the carpet off it and glass the outside and inside. Just resin is fine. Then....to tha boat!

I remember band pass boxes... We used to call them cheater boxes... it does make the percieved volume louder but at the expense of tightness. My ears like sealed boxes better for what I listen too. I do agree that building the box to the speaker makes a world of difference. In my younger days I had a ford ranger with 2 hi excursion 12's x'd at 60hz, 2 8s for mid bass running 60-120, then 2 sets of components...Today I have hearing aids.

Bandpass boxes don't work well in a boat. They need the cabin of a car to really acheive what they were designed for. With the open cockpit of a boat they just don't work as well, and with the small gain in output, I would rather have the much smoother sound of a large sealed box. I used a 1.25 cu.ft sealed box on my subs. This was only a 2db decreas in output from a ported box at 40 hz. But I had a 4 db increase at 80hz and the same output at 60 hz.

Sealed box is much easier to design and build for a boat. Ask anyone I have done a system for, or been on my boat. Sealed just works better.

Can anyone answer this?

the box ideally needs to be sized to the sub. and made air tight. So if you go boxed you will either have to build boxes and mount them or build the box around the existing seat. The other plus to a box is that on excursion the sub pulls a vacume. the sealed air pressure helps control the cone. Theoretically this allows you to have less power in the system. The enclosed area under the seat is to big. a 12" sub generally will be spec'd somewhere between 1 to 1.5 cubic foot. you need to figure the area the sub sticks into the box and factor that in. Of course we are talking perfection here, just get it close .

As far as using the seat as a box, I think it is doable. Sealed Boxes are not as picky as ported so if your box volume is a little off, no big deal. Box built to speaker spec is best but hey its a boat. I would put 4 10's under the rear seat and seal off the underside of the seat using some Marine Grade wood or such. That would actually make a box but you will loose the storage space.

Chris