Serious Equipment - Subwoofer Enclosures

[airman]

I recently gained full access to a quarter-million dollar CNC wood routing machine. For those who don't know what those are, here's a quick definition from wiki:

 

"The abbreviation CNC stands for computer numerical control, and refers specifically to a computer "controller" that reads G-code instructions and drives the machine tool, a powered mechanical device typically used to fabricate metal components by the selective removal of metal. CNC does numerically Directed interpolation of a cutting tool in the work envelope of a machine. The operating parameters of the CNC can be altered via software load program." -It refers to a metal milling CNC here, just that this one does wood.

 

So, in other words, I can put in an autocad designed file, with each of the faces I need, and it will cut them out of a 4x8 sheet of MDF precise up to 1/1000th of an inch.

 

After seeing this thing in action, I see there's a good market out for building/selling enclosures over the net. So I plan on doing so within the next couple of months - and a good bit of it too. The main thing is, I need to learn about acoustics/etc. I have read a lot about making enclosures/cabinets, however I still believe there is much to be learned. With such a precise instrument, I really would like to make enclosures that are almost, if not perfect.

 

I have played around with WinISD, and read a few tutorials about it as well. I guess, from what i've played around with, it doesn't give you "plans" and specific dimensions of what panels to cut out. I have also used an online utility, that I believe someone from the SoundDomain.com forum made, or was atleast in his sig. Someone with the name of "beer" somewhere in the name. It's actually how i have my current enclosure built, I just feel there is more to it that what I've done recently.

 

I'm currently a physics major at a community college, and I know a good bit about sound itself, in and out of phase, simple behaviors, etc. I guess it's stil a similar concept - with a few tweaks - that I have yet to grasp.

 

Regardless, I am definitely interested in utilizing this monolith CNC to my advantage, especially since I have full access to it. So...my proposal is simply this: if someone/anyone can provide me with the knowledge I need to do what I wish to do here I can provide a very, very well built box in return to anyone on this board, given the proper information/plans to do so.

 

By the way - I apologize for the wrong post. Only a wee bit excited about this new opportunity =)

[Verran]

Well, from my experience it will mostly depends on the speaker to be used. Any sub should ship with a frequency response graphed against box volume. Even amongst the same size subs, there can still be quite a bit of variance in desired box volume. So it may be tough to make a "one size fits all" box that you can mass produce.

 

Other than that, the only experience I can offer is that totally square boxes don't seem to sound as good. By that, I mean all 90 degree angles. I haven't made a sub box in a while, but my friends and I all thought that having at least one angled side tended to make a big difference.

[airman]

verran - you're right about the "one size fits all" statement. i was more or less referring to building custom boxes for someone who wishes to have one. you're also right about the square boxes. they have what is called a "golden ratio", which minimizes standing waves.

 

the formula is simply this:

take the desired volume of a box and multiply by 1728. find the cube rt of that. there's your first dimension.

take that number and divide by 1.63. there's your second dimension.

take the number from the first step and MULTIPLY it by 1.63. there's your third.

 

two problems lie within. we obviously know that each woofer likes a different amount of volume. however, what's the easiest way to find out how much it wants?

 

also, what about tuning frequency? vent length? etc.

[Guest christopher3393]

You might want to poke around the Sound on Sound Forum and start a thread.

[Verran]

Airman, all the stuff that you're talking about should be provided in the documentation for the subs. Every sub I've bought (or that I've seen friends buy) has always come with a frequency response page. It tells you the ideal volume for the speaker, along with (usually) the "acceptable" volume range. As far as port depth and such, I've called manufacturers for this before (MTX), and the tech support people were always more than willing to give enough info to spin my head. But assuming you don't feel like calling the OEM for every single box you make, you could just call a few and come up with a few designs that fit certain "classes" of speakers. Then you could just make 3-5 designs that all hit a certain range of volumes.

[p8baller07]

Don't bother - You'll invest about 2/3 in creating the boxes and only make 1/3 profit. Do something else.

 

Making a good box requires a LOT of work. I'm currently molding my own fiberglass box and its a TON of work.

http://forums.nasioc.com/forums/showthread.php?t=1257610

 

Thats my thread on Subaru forums showing my progress.

 

Every subwoofer needs a different internal volume to sound good, depending on different things.

 

Magnet size

Type of box, vented, ported, bandpass, sealed

size of subwoofer cone

frequency range

efficiency in db

size of coil

driver radiating area

 

If a subwoofer recommends .75 cubic feet internal space, you need that much. However you can be off by 20% +/- and it will still sound good.

 

Most people who charge for custom subwoofer boxes again make very little profit after all materials and labor is accounted for.

 

And I fail to see how a CNC will help cutting MDF, its nothing a Jigsaw couldn't do.

Most custom boxes are made from fiberglass anyway.

Edited May 6, 2007 by p8baller07

[Vasto]

Are your subs where the spair wheel used to be? Also what was the advantage in placing them there? (My subs are in a box I made that sits with the back flush against the back seat)

[Waco]

Every subwoofer needs a different internal volume to sound good, depending on different things.

 

Magnet size

size of subwoofer cone

frequency range

efficiency in db

size of coil

driver radiating area

Actually only the radiating area is important out of all those things you listed.

 

Also, never go by manufacturer specs - model up the driver(s) in WinISD or another similar program to figure out what kind of box you want to build.

[suchuwato]

And I fail to see how a CNC will help cutting MDF, its nothing a Jigsaw couldn't do.

Most custom boxes are made from fiberglass anyway.

 

Ewww.... fiberglass. Pick a nice wood, then carpet it - it'll sound soo much better (And by nice wood I mean from a tree, not some MDF rubbish)

[Waco]

Ewww.... fiberglass. Pick a nice wood, then carpet it - it'll sound soo much better (And by nice wood I mean from a tree, not some MDF rubbish)

Fiberglass and MDF are perfectly fine for enclosures. As long as the material is acoustically dead and strong it doesn't matter.

 

Please don't tell me you think MDF and fiberglass boxes sound bad...

[HuDDy25k]

You can trick the sub to think its in a bigger box by using woding thats wot i had to do but the i blew the sub oh well

[Waco]

You can trick the sub to think its in a bigger box by using woding thats wot i had to do but the i blew the sub oh well

Polyfill @ roughly 1 pound per sq. foot works well.