TEKTON IMPACT MONITORS

@tomic601: Years ago Danny designed a 2 cu.ft. (I believe) sealed sub enclosure employing double walls, with the chamber between the two filled with sand. I designed my 4 cu.ft. sub enclosures for the Rythmik F15HP DIY Kit using that same idea (with a 1/2" space between walls), provided my cabinet maker with the schematics, and had him cut the panels out of high quality MDF. I made the braces out of Baltic Birch ply.

I ended up abandoning the idea, having realized that at the low frequencies handled by a sub it is wall stiffness that is important, and robust bracing (spaced 4" apart) is enough to achieve that objective. At bass frequencies, the pressure created inside the enclosure by woofer excursion causes the walls to expand and collapse (like inflating and deflating a balloon), the source of sub enclosure resonance.

The unsupported 4" expanse of MDF wall between braces does create a small amount of resonance , but at a frequency high enough above the range handled by the sub to not be a problem. MDF is heavy, a double-walled enclosure measuring 24" tall x 24" deep x 18" wide and filled with sand really heavy, so having a single-wall/no sand enclosure was welcomed by me!

Coffee (or drinks) sounds great, let me know when you'll be passing through Portland. Have you been to Music Millennium? Pretty darn good LP inventory. 

@rixthetrick: I take it you live in Texas. Have you visited Danny Richie at his GR Research facility, located in Iowa Park? He welcomes visitors, and will demo his loudspeaker models for you. He sells his designs as kits (only), so they aren't for everyone. But you can at least hear what is possible at various price points.

And not to disparage Eric Alexander, but Danny considers loudspeaker enclosure resonance a very serious matter, his designs addressing it to a degree seen in few commercial plug-and-play offerings. Another designer who feels that way is Jim Salk (as did Albert Von Schweikert. Of course Wilson and Magico do, but you pay dearly for their approach.). Look at the bracing Salk employs in his speakers, the best I've ever seen. The enclosures he builds and into which installs Rythmik sub kits are insane, the best bracing I've ever seen. I copied it when I built my Rythmik subs; cross-braces every 4", front-to-back, left-to-right, and top-to-bottom.

If you send one speaker to Danny Richie at GR Research, he will thoroughly evaluate it's performance (frequency response, spectral decay---aka waterfall plot, enclosure resonances, x/o parts quality, etc. If he thinks a redesign of the crossover will improve the loudspeaker's performance, he will design one. All for free!

He sells a product he designed and has manufacture called NoRez. It is applied to the inside of the enclosure walls, to reduce or eliminate resonance if the enclosure requires it. I haven't seen the bracing on the inside of any Tekton, but word is they are rather lightly-braced, the speaker therefore perhaps suffering from audible resonances.

Danny will also sell you all the parts needed to build the x/o he designs for a given loudspeaker, and will lead through assembling it. Or you can have a local technician build it for you. He sometimes finds the x/o design of a speaker satisfactory, but the parts quality poor. He carries a number of audiophile-approved lines of caps, resistors, coils, wire, etc.