Sub box design?
 

Besides my primitive drawing can this design work? Plexiglass top with sub firing down and add a port that would fire into the main boat area. From the 20.5 side. The box would be a bow filler piece with a cushion on top if the seating was needed. It will be elevated 1.5 inches off of boat floor.

Dont see why it would not work but keep in mind each sub requires a certain amount of internal air space to function properly and does not really care about shape. If you have done the math and the air space is correct it should be fine.

According to the JL web site (12w3) it requires 1.7ft^3. The box should be 1.9 with the speaker and port reducing the box to the 1.7. I'm running out of options as I don't have enough room under the helm. HATED it in the locker so im really hoping this will work, gonna add some lights and graphics/stickers inside box to add to the LOOK. I was just wondering if the port not being on the same plane as the woofer face would make it sound crappy. Hopefully David or CHPTHRIL will chime in soon.

I still think it would be fine if the air space is corect. In the past I have had factory built potted boxes where the port was on the side of the box so not on the same plane.as the woofer I had the problem with our last boat where there was not enough room under the helm for a ported box so went with a sealed box for our 12w6 .It came out super nice and pounded way better than I expected.

You really want the port to share the same surface as the woofer, especially in a open air envoirnment. You will notice a difference going from locker to helm with it as you say. You will notice a difference with the port sharing the same facade from how you say as well.

Bill,
Sometimes you have to take what the boat gives you and make some compromises along the way.
In an ideal scenario here are a few things to follow, understanding that some of these recommendations won't pass in your application.
As mentioned above, the shape of the enclosure doesn't matter, the displacement matters, as long as it is a simple wedge or similar basic angled shape, although elongated shapes and small appendages should not be used. Also, the shape should not place the throat of a port too close to the back wall. And you have to compensate in length for a port throat along a wall or close to a corner....because near internal surfaces can serve to extend the effective port length and alter the alignment.
When down-firing, a long throw 12-inch should have the peak of the surround elevated 2.5" off the sole. Less than that begins to reduce the radiating surface area and costs you some output, not necessarily in a tight enclosed pickup truck cabin but in an open boat. It's especially a concern if the woofer output is firing in one direction only and not 360 degrees because now you are slot porting the front woofer output. And that changes the bass-reflex dynamics.
The orientation of the port relative to the woofer can matter. If the woofer is direct radiating and the port is rear or side-firing into an enclosed 5-sided helm cavity, then you are adding appreciable group delay....plus adding a pretty good boost to the lower bass output....at the cost of some bass SQ. Its better if both the port and woofer output exit on the same plane and into open air, which in a sense yours would given the down-firing woofer exits in one and the same direction.
If you aren't happy with the final sound you might consider sealed for your application.
If going bass reflex, I would like to see a down-firing slot port at the face of the enclosure that terminates a few inches above the woofer front slot. It will load against the sole better and water can't get in.
Again, I realize that you are going to have to make some adjustments that aren't perfectly ideal.

So I should have the port down foring too? I thought ports had to be certain lengths......i would only have about 7" of internal depth for the port which is why i figured putting the ports firing into the cabin would be better. I could go sealed and just make it a little shorter but then most of the sound would be in the bow. I was hoping the port would "direct" the sound more to the cabin?

This is a headache....lol. Ive already spent a few hours trying to make a box that would fit under the helm ( finally gave up ). Im making the box out of hdpe so i need to makeup my mind soon that crap is expensive, dont want to make a mistake.

It took me a couple trys to come up with a design that I was happy with and would fit. Built the test boxes with cardboard and duct tape then built the box once I had it right.

I definitely would not load both the port and woofer into a common down-firing slot as that is too confining. But rather the slot port mouth exiting the face of the enclosure on the cockpit side and turned 90 degrees downward. By design it would terminate several inches above the raised bottom of the enclosure. So now both the woofer and port would still load directly into the cockpit.

Better use some aggressive heat-bonding HPDE-specific adhesive on all HDPE joints, in addition to screws. You might do some research on that. I've never trusted gluing polymers for sub enclosures but I'm sure there is a good and proven method available.

HDPE certainly is expensive. Wood is cheap. I would first build a trial MDF enclosure.

Port like this one? https://www.carampsonline.com/product/10843

Or does the port type even matter much?

It doesn't make a difference within reason whether round, square or rectangular.
Most any shape will perform the same if it is a large enough surface area and is radiused to prevent noise, and does not have too narrow of a cross section.

Finally got the box built....still waiting on the plexiglass for the top. Hope it sounds good, i think it turned out pretty well. Although i should have thought more about wire management. :o

That is a very nice sub box right there. I built the exact same design with a Hertz Spl sub and used a slot port firing into the cabin. It's sounds great and hits hard.

Well....the sub didn't sound quite as well as I had hoped. Although I have not finished sealing it and figured out the port length quite yet. I also had a very LOW battery that I charged over night and will try again tonight adjusting gains and crossover points. I got the port length 7" to be tuned to 35 htz....good start?

Lack of volume or quality?

Its as close to the JL suggested 1.75 that I could make it. 3/4" marine plywood, the top plexiglass wasn't sealed so im hoping that was the issue.

Its a pic but I will take a stab.
1. your enclosure doesn't look sealed properly in the pic.
2. it will sound different in the boat than sitting on the bench as you are going to down fire it. make sure to properly space it and avoid firing into carpet.
3. it will sound like crap if you didn't seal the plexi side for sure.
4. your loosing output by not sharing the same wall for the woofer and port.
5. Read Davids post several times, this will probably inform you of why its not to your liking....

i know it would be WAY better for the speaker and port to share the same plane......that wasn't possible. The box is glued and siliconed for the bottom section so its good. The top hasn't been sealed yet because i was still messing around with the LED placement. I dont have enough room under the helm for a 12 so if this fails ill have to drop to a 10. I'm not trying to win any sound contests....just want a decent sounding/looking sub solution. I'll get it all sealed and placed this weekend and report back. Might have a few more questions.

That thing looks Legit! :) I say that thing is gonna Bang! Dammm haters! :) hey speaking of sub box design check out this pic Harold sent me of the new Wetsounds Sub box.

I sure hope so.....getting to close to warm weather to be messing around with rewiring and ordering more crap.

As I mentioned earlier in this thread I built basically the exact same sub box with the sub firing down, while a friend built his with the woofer and port both facing into the boat. I prefer the sound of my sub versus his, I really like the sound from a down facing sub in a boat. I found that as his gets pretty loud it doesn't sound nearly as clean, its more "Farty" or "poppy".

If you box wasn't properly sealed, it would sound like junk for sure.

"Farty" or "poppy" is a complete other issue and separate from the woofer orientation.

Sealed the box....made some amp adjustments. It is WAY better. I'm pretty happy, now i just need to adjust the port length for the tuning Hz. Whats a good target? As low as i can go? Or does it just depend on the music i tend to listen to? It has a 7" port currently supposed to be 35Hz.

Does the amp have a subsonic filter? Just note, adjusting the port length also effects the woofers net airspace.

Its currently a punch 400. It has an EQ dial.....same thing? I have the LP at about 80? Where should the EQ dial be set? I used one of those aero ports how much airspace do they take away? I was thinking it was very little since it was thinish plastic but i calculated the port, woofer and the corner bracing to be around .2. The box comes to about 1.9 based on what i could calculate.

Just read that the EQ pot is a boost for whatever pass filter is being used. I'll play with it some tomorrow. The neighbors im sure werent too pleased with me playing loud ass music at almost 10 at night. Although i WAS in my closed garage.

W3 manual says tune to 30hz.

go here to calculate port length based on box size (net of port), tuning frequency, and port diameter: http://www.psp-inc.com/tools2.html

If you can, try to tune it on the water. I know it's not the best time of the year but the sound in the garage and on the water will sound WAY different. What may sound amazing in the garage, will be very disappointing on the water.

Bill,

yes the wall thickness of the port is thin, but the air space inside the port is not part of the woofer's air space. So if you lengthen the port, you are subtracting air space from the woofer's net volume. Changing the port effects the tuned hz on two fronts.