Just wanted to update this thread based on this idea. On another forum, the designer of the JTR speakers suggest not modifying the cabinets for reasons I somewhat understand but not entirely.
Here is the link
http://www.avsforum.com/avs-vb/showthread.php?p=16794106&posted=1#post16794106 His post is #172.
He says that Dynamat lacks the mass to work in the kinds of cabinets used by the JTRs. Couldn't you just thicken the layer of Dynamat to increase the mass? This I don't entirely understand. The rest of his post I don't really understand either. Perhaps someone more knowledgeable like Chris or someone else could explain this to me.
I think you mis-understand my meaning of modifying cabinets.
Dynamat is actually a critical part of it; but not by way of a single side application. I typically add a lossy visco-elastic layer like Dynamat, then adhere a second sub-structure cabinet directly to the Dynamat. Doing this creates a constrained layer system. This uses the two stiff layers to focus a shearing action into the damping core, effecting maximum conversion of mechanical to thermal energy. Simply applying Dynamat to the walls has some effect, but no where near enough to effect large differences that are desired. And you can add more, but a threshold point is quickly encountered where even if you add 5x as much, the effect will be minimal on it's own. You really have to effect another mechanism, such as the constrained layer system I described.
Here is the measured wall vibration of an Ascend CBM-170 vs. one I modifed:
http://www.linaeum.com/productinfo/other/ascend_cbm170se_wmaxmod/wallvibration_oem_vs_mod.gif
The modified version added 1/4" visco-elastic damping(similar to Dynamat) plus 1/2" re-enforced concrete 2nd inner cabinet layer, then extensive steel bracing. This is MY idea of a modified cabinet. Here is a picture of inside the modified cabinet before I installed the new back wall:
http://www.linaeum.com/productinfo/other/ascend_cbm170se_wmaxmod/9.jpg
You can also do a similar modification without cutting the cabinet open. You would have to install the visco-elastic layer through the cabinet openings, then use a 2 part idustrial floor epoxy ($40 1 gallon kit available at Lowe's) to make the required sub-structure. You should adhere some metal screen to the back of the Dynamat before pouring the expoxy to ensure an ideal adhesion to the Dynamat. Build up to about 3/8" minimum wall thickness. Place some additional oak braces inside before pouring the epoxy. For small 2 ways, 1 Gallon kit should be enough. For the Triple 8s, at least 3 Gallons would be needed.
-Chris
