box for my momos

[dougie07]

Right now I've got each of my 3 momos in separate boxes, and they take up most of the space in the back of my s-10 blazer. So, I decided to make a box to put all three in so that they would give me a bit more room. Well, I started making the box out of some mdf I found in the garage, and while I was putting some of the pieces together, I thought "that wood seems kinda thin." Anyways...turns out, the wood is 5/8" thick instead of 3/4". Is this 1/8" difference going to cause any problems in the end? It went together pretty solidly, and seems to be quite sturdy, but I don't wanna end up putting the subs in that box and have it fall apart on me. Another thing is, I'm gonna do some fiberglass work on it as well, would I be able to reinforce the box with fiberglass if we conclude that the 5/8" mdf alone would be too weak? Any comments or suggestions would be helpful. Thanks much.

Doug

[neomagus00]

if you're putting all 3 momos (which ones?) in the same chamber, you will definately want internal reinforcement. the 5/8 should do just fine, but reinforce roughly as follows. cut the reinforcement board as shown, too. The idea, and i dont know why, is randomness. Thats why the holes are off-center and the board is angled. i dunno why, maybe someone else can tell you.

[PoweredByDodge]

randomness elminates / lessens "standing waves" -- standing waves are just sound waves that seem to pop back and forth in a destructive (rather than a constructive) manner.

inside of a box, randomness (usually in the shape of the box -- a triangle or trapezoid instead of a square... definately NOT a perfect globe) creates an environment where waves cannot reflect nearly perfectly and end up destructively interfering.

... at least i THINK that's the idea.

either way -- its a good idea. although personally i'd build one box with three individual chambers - one for each subwoofer, and reinforce as needed.

[dougie07]

They're the mm104's, and they're gonna be in separate chambers. I'm going to use some fiberglass to mold it to the shape of the space (the back seat angles up towards the back, and I want the box to sit firmly against it). I was guessing that the fiberglass would reinforce the box plenty, but wanted to check with some folks that have more experience w/box building. Also, I was gonna run some strips of fiberglass on the inside seams, to ensure good seals all the way around. Anybody see any problems with doing that? Thanks.

Doug

[neomagus00]

why don't you shape the box against the sloped seat, instead of adding fiberglass to the back? or is the fiberglass a part of the enclosure? and the internal fiberglass bracing should be cool.

pbd, that's what i thought, but i didn't know enough to make the assertion.

[dougie07]

I just figured it'd be easier to add the fiberglass rather than cutting the angles on the wood. I don't really have the proper tools either. It'd be a pain tryin to cut the angles w/a circular or reciprocating saw.

PBD,
I've read your post a couple times over, and maybe it's just me, but it sounds like the two statements contradict each other. The first one says that randomness ELIMINATES the 'standing waves' that are destructive, but the second one says that randomness CREATES an environment where the waves are destructive. Am I understanding your post correctly? Or maybe it's just too early for my brain to be working right. Probably the latter.

Anyways, thanks for the input guys.

Doug

[PoweredByDodge]

the 2nd part would agree with the first if i used commas properly.

the randomness creates an environment where the standing waves cannot reflect nearly perfectly, causing destructive interference...

or better put -- it creates and environment that wont allow them to reflect perfectly and will NOT allow them to cause destruct. int.

bad english - good pizza... :)

[dougie07]

mmm, pizza.....wha??? it's not even lunch time yet?

I think I get it now. So, I gotta make sure the inside shape of the box is as far from a sphere as possible? If I actually get the idea here, it would make sense. If the inside of the box is a sphere, the waves will bounce off every which way, whereas in a cubic box, the waves reflect straight back. Am I understanding this correctly? If not, it may still be too early. Or maybe it's because I'm hungry...hmm. Well, thanks for all the help.

Doug

[Jstas]

Don't even bother with the fiberglas on the inside. Hell, don't even bother with fiberglas at all. Don't make the box overly complicated and you can make all the angle cuts you need with a hand-held circular saw. Most saws have a deck that can be angled so use it. On the inside, use caulking in the joints and shove it in with your finger. Let it dry and air out the box for a few days, cover the outside with carpet if you like. You can also line the inside with acoustic batting (polyfil stuffing you can get at any craft store), mount your wires and speakers and shove it in the truck.

If you already lack the proper tools, why make things overly complicated? Make a design that works best for what you have.

[neomagus00]

oh yeah... seems fairly obvious, but make sure you account for the reinforcement in your volume calculations. and instead of fiberglass, you can add mdf along seams to reinforce. that'll make a rock-solid box. just remember that internal wood takes up space.

and while im on it, do the box rec's by polk include the displacement of the driver? ie for a 10, it says .66 cu.ft. is that total box volume and then you put the driver in? or is it how much free space you need at the end?

[dougie07]

I didn't notice if the saw had an adjustable deck or not, but I'll have to check that out cuz that would make things a bit easier. I wanted to try some fiberglass, because it looks like fun. I like building stuff, and fiberglass seems like it could be useful for more than just sub boxes. I also like to make some things somewhat complicated. I like a bit of a challenge, and I don't get much of that at work, so it helps out to do this kinda stuff at home (school helps out a little bit, too).

I think the volume is before you put the driver in, but that question was asked on here before, so I'll look it up before I go any further on the box.

Thanks for all the input and advice.

Doug

[sntnsupermen131]

you want to build the box to .66...the displacement of the driver is included
as far as fiberglassing, id do MDF
its stronger, not going to flex as much, unless you want to build the box pretty thick
and i really wouldnt use it on the inside of the box
fiberglass is very reflective
reflective=bad
chaulk would be the way to go
and id build the box with 3/4" MDF or 3/4" cabinet grade birch plywood
the plywood is going to be more expensive, but its lighter and stronger
that plywood is also somewhat reflective, so you might want to put some eggcrate foam to line the walls, or poly fill
egg crate would work better, poly fill is easier, unless i was doing a fiberglass box, id use poly fill, dont buy it from a car audio store either...they jack up the price
go to wal-mart...its a stuffing for pillows and comforters and such
like a synthetic cotton
but screw all the sides together or use ribbed nails...and line all of the edges with liquid nails
liquid nails well help hold AND seal it for air leaks
- Cody