Speaker cabinets: How important is inert

Well designed cabinets are certainly a major factor in a speaker's overall performance, but a very "dead" cabinet is not the only effective means of producing a good speaker. Two examples of the alternate route would be the Harbeth speakers and Audio Note speakers.

With Traditional drivers, The lower the resonance of the cabinet materials used, the less you hear the cabinets in your music. Typically this is achieved by useing very dense materials. Bracings purpose is to reduce cabinet resonance. If you can come up with a space age material, that will not flex(flexing would be a problem) or give and is "DEAD" you should have a winner. Until then, we do what we do. Tim

"Two examples of the alternate route would be the Harbeth speakers and Audio Note speakers. "

What route DOES Audio Note (UK?) take? They look like a Radio Shack project speaker, and imo, don't sound much better than my first pair of SoundDesigns in 1977.

With speaker drivers housed in cabinets, the fundamental issue is what does one do with the rear wave from the back side of a driver? That wave is just as strong as the front one. That energy does not magically go away, so it must be taken into account.

A dense cabinet in and of itself will only trap that energy inside the speaker and it will reemerge through the speaker cone as delayed sound. This smears the sound.

Ports and other devices work only in a lower range of frequencies. Padding and stuffing only work well at upper frequencies. However, if one is not careful, not getting rid of this rear driver energy can easily create issues in the lower midrange where our hearing is particularly sensitive.

Harbeth & classic Spendors use the BBC damped thin wall design. Other speakers use other approaches, but by itself, a cabinet that is simply dense doesn't address the issue.

Like any engineering problem, it requires a system approach to address the problem.

"but by itself, a cabinet that is simply dense doesn't address the issue"

Actually it does address the issue. Not 100% But generally. A speaker has a specification called vas, this is the Equivelant air volume or the volume of air that has the same compliance as the speakers suspension.
The suspension i.e. voice coil assembly, spider and even cone material affects how the driver reacts to the air behind that driver. That is why In a sealed box a drivers frequency curve will develope a peak as you shrink the box size or develope a dip as you increase the box size. This happens on any traditional cone type speaker regardless of size. Cone breakup because of that back wave is what causes the smearing effect that you speak of. The right cone material will not have that smearing effect of back wave. In general, cabinet stuffing has three purposes, to break up standing wave, to cut resonance and to trick a driver that it is in a larger box, by changing the time that it takes air to travel within the speaker box.