Box design thread
If anyone wants, I'll give a quick tutorial on how to design sub boxes. Topics to be covered would include speaker selection, box designs, construction techniques and testing. I will not cover horns. I will cover sealed, ported, dual reflex ported, bandpass(4th order only), and transmission lines. This can be for home or car.
To get the ball rolling, a good program to use for designing your own enclosures is called WinISD. The current version is WinISD Beta and is freely distributed by LinearTeam(x). It has a decent database of existing drivers and is a fairly complete program.
If anyone needs help designing a box, please post here and I'll follow-up with you. Remember to link to the speakers Thiele-Small parameters. They are listed as: Fs, Qts, Vas, Sd. These are the bare essentials. Addiotional parameters include: Qes, Qms, Le, Re, power handling, BL, Xmax.
I used WinISD to design a box. I plan on having a friend assemble it for me in the next few weeks or so, I can't wait. I'll be sure to share my results.
Here are some general tips when building your box.
1) Liquid Nails or carpenter's glue(yellow glue) is the glue of choice for MDF. If your cuts are not going to be very precise, use the liquid nails. If you're using a tablesaw, carpenter's glue.
2) MDF is the choice of woods for building your subwoofer box. I've built bookshelves out of birch plywood, but we're talking subs for now. Get yourself some 3/4" MDF.
3) Brace the crap out of your box. For small boxes( <1.5 cubic feet), no bracing is required. For a box about 2 to 3 cubic feet, a few braces made from MDF will do. I try to cut a strip of MDF 3" wide to jam in between the walls. Start by bracing the biggest surfaces. The brace does not need to be in the middle of the panel. Bracing has many advantages, from stiffening the box to breaking up resonance modes from the enclosure.
4) Clamps are your friend. If you don't have the money for good clamps, pre drill the pieces and the glue it. Remember to pre drill one panel, assemble it with screws, then pre drill the second panel, add that to the box and so forth. Only once eveything is finished and assembled with screws should you remove the screws and glue it.
5) Consider drilling the speaker holes before assembly. The hole might be so large that it butts up against a wall making cutting such a hole by jigsaw impossible. The best hole is obtained from a router with a circular jig. For the safety of your router, use multiple passes. MDF is nasty nasty wood.
6) Don't mount a speaker from inside the box unless you really have to. You will kick yourself in the ass when it blows and needs to be replaced.
7) You can mount a port wherever and however you want. Sadly, the best port location is as close to the speaker as possible and flush to the box. However, if you want to, you can have a port with two right angle bends and then a section 6 inches sticking out of the box.
8) Forget the dog, T-nut are your best friend. It's a nut for a bolt that has a sleeve surrounded by teeth to sink into the wood. Simply drill a hole for the sleeve to fit into, and hammer the nut in from the back. The bolt part needs to be well aligned to go into the nut, so be patient. Voila, secure hold on your speaker to the box.
Using wood screws in MDF to mount a speaker is asking for trouble. As soon as you remove the speaker just once, they loosen a bit. They'll just get looser each time until they're useless.
9) I've always soldered subwoofer internal wiring, but I figure crimp connectors will do just fine.
10) The 10th and most important commandment. Thou shall make thy box air tight or feel the wrath of the whistle.
Seriously, caulk the inside joints and LET IT DRY. Silicone caulking is just waiting to chew through that nice foam surroung. A few days will poor weather or 2 days with good weather will cure it up enough to be safe. A ported box will vent for the rest of its life, so you can cheat and put it together early and use the 'break-in' to get the last bit of gases out.
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