Sub Boxes

I have always gone with braced .75" mdf lined with fiberglass resin. Havent ever had any flex. If you are putting up some big #s on the meter .75" may not be enough though.

 

it all depends on your bracing, i could make a box just fine with particle board...i know some very knowledgable audio people who unfortunately do not have MDF within 100 miles of them (well maybe 50 or so) and are basically forced to use particle board...not to say that pb is as good as fb...but you can make due with almost anything that you have in those areas...

birch is a good material, a bit lighter, etc...

fugyaself has the way to go...what i've done recently...sometimes i go a bit overboard on the bracing...but it's not a big issue...i also use more screws than i see most people use....maybe i go overkill, or other people just don't do enough...but i want my box TIGHT at the edges...i think a lot of people don't realize the need for over-bracing ... a guy that i know that is very good at building enclosures (you should see his first ever fiberglass project....it's...huge, and good...) apparently didn't have enough in this case:

http://www.caraudioplanet.com/forums/viewt...ghlight=bracing

bracing is pretty easy and so many people overlook it

i have other thoughts on box building but until their address specifically or it just has to be said i'll wait

 

I've heard far to many people say that their box doesn't move at all when in fact it is moving enought to reduce output by a good deal.

Movement the width of a fingernail can make fairly large impact on the output.

Dan had some stuff to say about this when looking at a square box for a tempest. (See below)

The math is pretty simple. Look the surface area of your box and then look at the surface area of the speaker and you'll see about how much is being taken away from the speaker when it moves.

I also remember reading about what is best when looking for different types of wood and enclosure bracing.

I remember that more ply = better generally and there were two other rules.
Circle bracing is better than other types.
Use 90 degree angels.

Can't remeber the other stuff, I think it was in audioxpress.

 

There's not much sonically that makes particle board inferior...
But there are plenty of reasons MDF is superior to it:

• It's got a rough texture, where MDF is not only smooth, but it leaves relatively smooth surfaces behind even where cut.
• The above property is not only important for cosmetics and finishing options, but for jointing seams as well.
• Particle board swells - badly - in damp environments. MDF is much less vulnerable. Cars can be bad places.
• Particle board strips easily when screwed into, where MDF bites screws better.

There are reasons why MDF is sonically superior to Grade-A (furniture grade) Birch ply as well:

• MDF has better damping properties (ability to absorb, rather than reflect, sound energy)
• MDF is smooth on both surface and cut edges, where grade A ply is smooth on surface, but cut edges are rough
• MDF costs much less money than Grade A Birch ply

There are also reasons why Grade-A (furniture grade) Birch ply is superior to MDF:

• It is much lighter, in weight, than the very heavy MDF
• Grade A Birch ply is more rigid than MDF, will resist bowing better
• Raw Birch ply is arguably more attractive than raw MDF - inherent in it's intended furniture-grade purpose.

It all depends on your needs.
The ideal material, IMO, would have these properties:

• High damping properties (absorbing, rather than reflecting, sound)
• Light in weight
• Very rigid
• Forgiving "machinability" (easy to cut, leaving smooth cut edges behind)
• Low cost

High damping properties are high on my list...
Which is why I'd suggest against lining your enclosure with fiberglass resin...
Cured fiberglass is very reflective, inherently.

I'd also suggest not just screwing your enclosures together...
Glue ALL your edges - liberally. And even still, I'd recommend sealing all the joints from the inside, as you assemble.
This will ensure not only a well-sealed enclosure, but one that's got much more structural integrity... believe it or not, a properly jointed glued joint will have more integrity than the wood itself. The screws, IMO, simply act as convenient little clamps, to draw the MDF together tightly as the glue cures.
The sealing of the seams from the inside (such as running a bead of Silicone adhesive along each joint) will ensure any pinhole leaks are sealed up.

I'd also brace the enclosure, which will not only contribute to a more rigid enclosure, but also to break up any waves being bounced around inside the box, because no material is perfect in terms of damping... reflections will still happen.

And I've used all of the above...
I usually definitely use MDF... but my Civic is a 3/4" Grade-A Birch ply structure (at least the top, sides, front and back), with a fiberglass base contoured to the shape of my spare tire well (the odd curves and ribs helping to diffuse any reflected waves off it's surface, minimizing the harm of using such an acoustically reflective material).

Hope this helps!

 

Check out the bracing in this pdf

http://www.adireaudio.com/Files/VentedTemp...pplications.PDF

 

There goe smy plans to use this nice sheet of 1/2" billet aluminum I got for free. Would have made a sweet looking box.

 

In regards to Birch and reflections, would adding a layer of a liquid deadener along the inside cut down on the reflections? I'm a fan of Birch, almost entirely because of its weight. In my VW, if I had made my box out of MDF, I'd never be able to get it into or out of my rear glove compartment(trunk). Birch is also very pretty, I stained my last box with a red oak stain, and gave it a satin polyurethane, it looks beautiful. The other thing I really like about birch is that you don't have to wear anything to protect yourself from the dust. When you cut MDF(or do anything that causes dust), it's recommended that you wear respritory protection, because the glue used in MDF is dangerous(I don't know exactly why, I think it's a carcinogen). MDF is much easier to sand though. MDF also is more prone to flaking(I don't remember the technical name) at the edges.

 

I've seen it done!
Not with Billet, but steel...
Picture taking a radio, and lowering it down into a steel garbage can as it plays loudly...
You can picture that, I'm sure! :lol:

No reason why you couldn't do the enclosure out of MDF or other material, and then build beauty panels out of the Billet.. that would offer even better cosmetic options. B)

 

Birch isn't bad to begin with.
I'd suggest if anything, lining it with eggcrate foam. Parts Express sells it downright cheap for good sized pieces of it.

Actual damping material probably wouldn't help much, although the liquid stuff would be better simply because of it's uneven texture it would leave behind.
But eggcrate foam is easier, cheaper, and better.

All materials will chip or get damaged if you drop it or abuse an edge, but IMO, I think Birch holds up the best, followed by MDF, while particle board chips the easiest... more along the lines of "disintegration".
The glue I believe is the same as particle board, btw.. but MDF has not only finer fibers, but metal particles and other things that just aren't good stuff to be sucking down.
I've got a spent paint respirator (it's been exposed to oxygen for longer than it's canister's life expectancy) that I try to remember to throw on when I cut, it's better than cheap dust masks.

 

You can always add polyfill to the enclosure

Smaller enclosures (like those most commonly found in cars) shouldn't suffer from internal reflection much anyways

I agree. I like Birch. While I find it very difficult to work with and pricey, the beauty, strength (less bracing YAY!!!) and reduced weight all make it my personal fave.

As far as rough ends, that is easy to deal with... Simply put some glue in the end seam (where small pieces may be missing, or where a rough spot is) and fill it with some sawdust (we all know there is plenty of that laying around in your shop ) and/or woodchips . I usually do this wherever I am going to place a screw with birch, just to be on the safe side.

 

Seth...
You need to post the link to the crazy tongue-in-groove type jointing you did on that one enclosure (that's not the Brahma box, is it??)! B)

Also, for the edges... I use a lot of DAP's Plastic Wood, for MDF or Birch ply, for finishing edges after assembly. But I like to paint, not stain... generally textured finishes, since they are much more forgiving of minor imperfections.

 

It was the dual Shiva box Chris...

http://www.sounddomain.com/memberpage/261051/6

I incorporated it into my BB tutorial above, and linked that directly to the page. Below are the joints apart, and assembled. also the finished product .





They forced a perfect square and doubled the surface area, adding stregth to the glue joint. Clever cut really, used in high end cabinet making. The router bit alone was over $100.

I never expected the current ported Brahma box to stay in the car for long, so I never went that far with it. An upgrade is going to be done this winter. All I can say is sealed box, Plexi, sealed off from the trunk (going to try to eliminate that annoying rattle ) so all energy fires into the cabin.

 

Not too thick. It will not take up too much space, but it may be best if you are a crazy perfectionist to add a bit of extra space to account for it.

Polyfill will help absorb some of the refected waves in the box. While it does make the box "appear" larger, there is no reason to build it smaller. Who doesn't want a more accurate subwoofer system in their car? Adding polyfill will basically lower QTC and that is a bonus. Why try to defeat the benefit if you can fit the origional box in your vehicle anyways ?

 

Eggcrate foam isn't too thick... about an inch on average (but varies, obviously), and soft, so I wouldn't imagine any adjustments would realistically need to be made.
Polyfill does make it "seem" like the enclosure is bigger... but not a lot, not enough to try to compensate for. Only benefits to "bigger", not drawbacks that need to be compensated for.

 

What about solid woods like oak, walnut, ash?

I know there is a weight issue and cost for most people with solid hardwoods but will they work. I am assuming a thickness of .75 to 1 inch.

 

Sure, but as you say... exactly. Weight would be the issue, and for what gain?

 

I can get these cheeper than DC plywood or mdf.

Dirt Cheep...