Sub project-construction technique questions

[wunderaa]

Ok here goes.

I've built a 500WPC stereo amplifier specifically to drive two JBL GTO1220D subs. Each speaker gets its own channel of bass-driving juice. These subs were selected because their response in a vented enclosure is relatively flat (easily controlled by a nice 9-band sub-EQ).

As for the enclosure, I know I want them both in the same box (though obviously in separate chambers). Trouble is, woodworking is not my forte and I'm stuck on what construction methods to employ.

I was thinking of using 3/4" MDF, but have my doubts as to how it will hold up with up to 1000W of power coming through the speakers. I foresee a lot of wall flex if braces are not used.

So my questions are:

Should I use a thicker MDF?

What type of joints should I use? Glue and screw or other?

If I should use bracing, what kind?

Any and all suggestions will be appreciated!

JBL Sub Site

Box Specs and Performance

[forr]

My recommandation, only valid for for sub boxes where the dimensions are far more small than wavelengths, is to build them as rigid as possible whatever the techniques or materials you use.

~~~~~~~~~~ Forr

§§§

[simon5]

3/4 inches thick MDF is a nice start.

Good wood glue is enough, it's even better than screws but you need wood clamps. You can use glue with screws if you don't have wood clamps.

Remember to seal very very well your box, any air leak, as small as you could imagine, will compromise the performance ALOT.

You should use bracing.
I suggest this kind of bracing...

[David Gatti]

Use 1 inch MDF, 18mm just isn't rigid enough. Make sure it is well braced, preferably with shelf braces.
Draw up plans, take it to a local supplier and get them to cut it all for you. Saves a lot of dust and time.
The drivers don't need to be flush mounted, so you can cut the holes with a jig saw if you don't have a router.
Screws will help hold things together while the glue dries if you don't have clamps. I use cleats in all joints to guarantee an air tight fit.

Cheers
David

[wunderaa]

Thanks Dave!

I've started construction using 3/4" MDF (1" was not available at any local lumberyard). My neighbor has a nice woodshop so I used his equipment to make the cuts I needed. The outter shell is complete and now I will be starting in on the bracing.

Photos soon. I'll also run a separate thread detailing my DIY sub amp.

~Aaron

[kingdaddy]

If you woodworking skills are a bit shy, then I would try a Sonotube sub, they’re easy and no bracing is necessary.



My Sonosub Project
http://kingdaddy.linaeum.com/Sonosub/





No need to get fancy like mine, there are many others out there much easier.

[David Gatti]

Originally posted by wunderaa
Thanks Dave!

I've started construction using 3/4" MDF (1" was not available at any local lumberyard). My neighbor has a nice woodshop so I used his equipment to make the cuts I needed. The outter shell is complete and now I will be starting in on the bracing.

Photos soon. I'll also run a separate thread detailing my DIY sub amp.

~Aaron

No worries Aaron. 3/4" will be OK if you make sure you brace well, especially around the front baffle.
Looking forward to the pics.

[wunderaa]

Originally posted by kingdaddy
If you woodworking skills are a bit shy, then I would try a Sonotube sub, they’re easy and no bracing is necessary.



My Sonosub Project
http://kingdaddy.linaeum.com/Sonosub/





No need to get fancy like mine, there are many others out there much easier.

Beautiful project! I would love to be able to hear it! Are you happy with the sound?

I would've liked to have done a sonotube, but may have to put it off until the next sub I make.

Thanks for the reply!

[kingdaddy]

Like any sub, the alignment and enclosure size is very important to the sound quality. Too big a box yields a soft less punchy sound that may be to mundane for movies, too small an enclosure will make the driver bloated and uneven at certain frequencies. Port size and tuning it also a bit of an art. I made several prototypes and tried them out to get the sound I wanted, I had enough Sonotube to make two at a time, one big and one small, and then A/B compared them side-by-side. This kind of testing will give you a good reference to what the different enclosure sized will sound like with a given driver. I prefer a slightly larger then optimum box for a smoother FR and better extension.

To answer your question, I think these sound great, as good or better then any other box sub I’ve heard, but not as good as my recently completed 4-18" Avalanche IB, which is why they are now sitting in a back room. I'm actually thinking about selling them, but I doubt I could get what I put into them.

[dscline]

I have a related question: are there no rules of thumb for the maximum spans for planning bracing? I would think that, for example, 3/4" MDF, when used for a specific amount of power in a specific size enclosure, would have a specific "maximum recommended span" between braces and/or box corners. But I've never seen anything that gave such guidelines. Do any exist anywhere?