We also agree that an acoustically inert loudspeaker cabinet will result in increased costs due to increased damping materials, weight, shipping costs, etc.,
Where we may disagree is how important this is to the sound quality of the loudspeaker. My question is, "How mechanically inert/damped does the speaker cabinet have to be before you've reached the point of diminishing returns where there are no audible improvements when listening to music/speech/film signals?"
Is this something you have formally tested?
Years ago, Stanley Lipshitz and John Vanderkooy at the University of Waterloo did some experiments where they built and tested a number of loudspeaker cabinets of the same dimensions and volume that varied from being completely inert to being very flimsy with almost no bracing and thin cabinet panels. They then measured the effect of the different cabinet constructions on the measured acoustical response of the loudspeaker noting the change in frequency, level and Q of the resulting resonances. They found that the audibility of these resonances were in most cases below the absolute detection threshold of audibility for music signals using the threshold data from the
resonance detection study Floyd Toole and I conducted at the NRC.
Lipshitz and Vanderkooy concluded that you could get away with loudspeaker cabinets that were relatively light-weight and flimsy as long as you had adequate bracing judiciously placed etc to make the resonances fall below their detection threshold.
This suggests that building massive speaker cabinets like the type you are describing may be overkill in terms of the audible benefits. It would be interesting if you could validate whether or not this is the case. Maybe you already have?
That is not to say, high-end (i.e. expensive) audio equipment shouldn't be heavy since may people associate the weight of the amplifier or loudspeaker or cable with its quality and how it will sound: Hearing is Believing is Lifting