Not concerned about MDF as long as the execution is perfect (it's a long list), it's totally sealed and it's elevated to allow for drainage and evaporation. An MDO plywood or Medex fiberboard are constructed with solvent-based adhesives and are superior. A high grade birch plywood like MLA mentioned is also a great choice. It requires too many fiberglass layers (work) to get the same rigidity as .75 wood construction and to make a fiberglass enclosure adequately inert. Some fiberglass production boxes are great but are sprayed with a chopper which greatly reduces the time investment.
IMO, the JL Audio W7 series woofers are the finest reference woofers available...period. Incredible R&D went into these woofers. Every design is a trade-off. NO exceptions. The W7 is about extra controlled excursion, deeper low bass extension and a wide linear bandwidth. The cost is the extra power it takes to achieve those benefits, particularly in an open field boat. A bit less excursion and a bit less bandwidth can result in a greater internal efficiency. So if I was looking for a top subwoofer I might also consider the JL Audio W6 series specifically because it is a less demanding woofer to drive in an open field.
I would design my maximum displacement enclosure first that fits the boat and let that dictate my best subwoofer selection.
Now I am probably getting ahead of myself, but I use 3/4" (18 mm) Baltic Birch, then glass over it and paint for a nice finish, should I plan on adding some interior damping material?
It's not required but no more than one layer of 1-inch thick polyester batting to the interior walls.
Originally Posted by EarmarkMarine
Wow! This is going to be a little more involved than I originally thought. I just came back inside after finally yanking (and I mean YANKING) the existing Chinese sub enclosure out. What I had originally thought was screwed into the boats structure was actually just crammed into the driver's footwell and wedged under the steering cable assembly - nice, real nice!
Anyway, after putting the R12 back in the enclosure, I moved around the boat (somewhat), stuck it near the pass thru - pointed both ways, on top of the driver's seat and up front and on the back seat. After all that I would like to mount it on the pass-thu's vertica surface - But!!!! I don't think I will be able to fit a sub there due to various factors including the build of the pass-thru and the location of the steering assembly.
So, turns out I will need to build a box (or two) to try to fit - under the helm, missing the steering assembly and cable, then as David said, go from there!
I am starting to fab my sub enclosure today for up underthe driver's footwell area , I will be making templates then use BB (Baltic Birch) for the final box.
In the space that I have there is an open area through the bulk head, but it is about 1/2 to 2/3 the available width of the enclosure (more detailed dimensions to follow).
- Should I try to use this area?
- Or keep the enclosure having a constant cross-section? leaving less volume
Thanks again, Eric.
Without specific dimensions and a hard visual I cannot really say. But I will give you this general guideline. If the enclosure cross section is reduced too much or the enclosure is too elongated or you have appendages that are too extended or too separated by a path reduction in surface area, then the benefits of that extra displacement is wasted...and it can set up some strange aperiodic issues. Do you know how extra tall and shallow in-wall home subwoofer enclosures sound awful? Some of the same principle at work. Angles and compound angles are fine. Any irregular shape is fine. Unusual shapes with inherent narrowing between chambers is not. By asking the specific question I sense you already have an analytical feel for it. And sense it is rather hard to find absolute data on this, trust your eye.
I got my sub-enclosure completed today and now have some questions.
The photo shows the overall shape of the template piece.
And the cross section drawing - the box is about 23" in length which gives an approx. volume of 2.40 cu. ft. (not reducing for the thickness of the enclosure framing material or the sub itself)
I also modified the drawing to eliminate the top portion of the enclosure;
The first mod (#2) has an interior volume of approx = 1.92 cu. ft.
The third (#3) and smallest (again at ~23" width) has an interior of about 1.58 cu. ft.
I dont think that I can any bigger than a 10" sub,
- Does the extra volume of #1 help? or is the shape too strange?
- I may be able to fit two tens - would I gain anything or just cause more problems (seems like I would be using up a lot of the gross volume)
- Any comments on cross sections #2 or #3?
- Would going to two Eights help?
Extra volume? That depends on the woofer. I would want a final Qtc for a sealed box around .8. You will have to convert to the interior displacement and know the woofer displacement in order to arrive at a true net. Then, choose the maximum woofer surface area that will stay within the optimum Qtc range. Two 8"s versus one 10"? Two 8"s will have more surface area and more output vesus a single 10" of the same series while one 10" has lower deep bass extension having a lower inherent resonance. Multiples increase output but not bandwidth. However, past a point the enclosure dictates the deep bass extension so I would return to the maximum enclosure volume with an ideal Qtc for a particular woofer.
The largest enclosure shape is fine. Shrink it to match the woofer if necessary. Move the woofer as far as possible away from the bottom (as oriented in the illustration) angled surface. No problem with the shape other than it weakens construction. So place a corresponding slat behind each seam and add a couple of thin front to rear stiffeners. Also, calculate those into the internal displacement.
When using multiple woofers keep in mind the final impedance. It will be less of an issue with a strictly regulated amplifier but can be very important with an unregulated amplifier.
Ok, so this is what I came up with,
So I have decided on a JL Audio 12W6v2-D4 (Jumpered for 2 Ω)
- I can't fit (2) 10's
- I can't fit a W7 - 12"
- I can fit a W7-10"
- I can fit a W6 - 12"
The W6-12's design parameters are;
Fs 25.0 Hz
Vas 2.82 cu ft
Driver Displ = 0.090 cu ft
Using the recomended Qtc = 0.8, I get a net box volume of 1.31 cu. ft. and F3 = 40 hz, Gross volume = 1.4 cu. ft.
My interior cross section = 0.91 sq. ft. and I ended up with the enclosure below.
So, does this look correct?
And did I get the math correct?
Is this a good choice?
Is it time to start cutting wood?
Is it time to start picking amps?
I especially like your W6 choice in a boat. While the JL Audio W7 is considered by many to be the industry reference subwoofer and is certainly my number one choice in a vehicle, the extra excursion always comes at a price of lower internal efficiency.
Having installed a ton of these with a variety of amplifiers, I like the JL Audio HD750/1. It is a little over the recommended JL thermal rating for the 12W6 but JL rates power handling very conservatively and the extra headroom makes a difference in an open field environment. I also like the fact that the HD750/1 is strictly regulated and the performance is more on par with a 1000 watt unregulated amplifier. Power is stable over a broad range of load impedances and a broad range of supply voltages. With this amplifier, every soild state element in the signal path is always operating within it's ideal parameters under a variety of conditions. The JL Audio HD750/1 is also highly efficient Class D.