Yes, I agree, and I do understand. In the soundproofing site they describe the difference between sound "blocking" (generally reflection) and sound absorption. Cork is a good absorber, but not a good blocker. In my 2-way design, the same portion of the enclosure necessarily handles the whole range from bass to about 500 Hz. A bass enclosure is generally made stiff to move the panel resonance frequencies above the bandwidth of the woofer. A midrange enclosure is generally made "floppy" (relatively speaking), to move the panel resonance frequencies below the bandwidth of the midrange. In my design I don't have the luxury of "both", so I have to try to make it stiff for the bass but lossy for the midrange.
An important concept that is often overlooked in both constrained-layer damping and sandwiched construction (with damping material in-between) (which is not constrained-layer damping) is that in order for the damping to be effective, something's gotta move. That is to say, one of the layers has to be allowed to vibrate so that the damping material can ... damp. It offends the sensibilities of most people to build a "floppy" enclosure, so most people (myself included) opt for very high stiffness and relatively high mass, so that whatever remaining movement is minimal. I'm just considering alternatives to that.
