Here's a good one. This is a 1.5 cubic foot sealed box for a single SW-12-04 Direct Servo sub.
![](http://www.gr-research.com/images/solid1.jpg)
This is the inner box. It is built from 3/8" thick MDF on four sides.
![](http://www.gr-research.com/images/solid2.jpg)
The braces are 2.875" apart and are made from 3/4" MDF. The woofer mounts in the front (as shown) and the plate amp will mount on the panel on the rear.
![](http://www.gr-research.com/images/solid3.jpg)
Next some 3/4" wide and 3/8" thick MDF strips are cut and laid in line with the braces below.
![](http://www.gr-research.com/images/solid4.jpg)
When this is set into the outer box it leaves a 3/8" thick space between the walls.
![](http://www.gr-research.com/images/solid5.jpg)
Next five sides of the outer box is built around it.
![](http://www.gr-research.com/images/solid6.jpg)
Additional 3/4" thick pieces cover the front (where the woofer mounts) and the back panel where the amp will mount.
![](http://www.gr-research.com/images/solid7.jpg)
Then comes the fun part, pouring in the sand. Shaking it, rocking it, and beating the sides with a rubber mallet insured that the sand was forced in as tight as possible and as much as it could hold.
![](http://www.gr-research.com/images/solid8.jpg)
Then the last panel is glued on sealing it up.
![](http://www.gr-research.com/images/solid9.jpg)
So far, so good. It is a rock solid box.
Next I cut the amp hole in the back.
I also plan to seal the back of the amp from the inner air space.
More to come...