Bloated speakers/weight wise

Bartokfan, the front wave from your speaker drivers puts acoustic energy into the room and the rear wave puts an equal amount of energy into the speaker cabinet. Your room is measured in hundreds of cubic feet, but the speaker cabinet is typically measured in the single digit cubic feet. Even at non-loud volume the energy within the speaker cabinet is relatively high and it is this energy that is a major cause of cabinet vibration. The soundwaves bounce around within the cabinet are eventually dissipated, but a certain portion of the sound makes it through the enclosure, or back through the driver and results in a smearing of the original acoustic output. Most attempts to solve this problem involve techniques that will make the speaker heavier. Of course you could take a completely different approach and eliminate the cabinet altogether and let the back wave escape unimpeded into the listening room. This raises another set of problems, but it has been done successfully by several manufacturers.

I see no correlation with speaker weight and the size or quality of a soundstage.

Zaikesman, the M-S speaker has an incredible design for the cabinet. I don't know for a fact, but I suspect the cost of the cabinet relative to the total production cost of the speaker is quite high.

My speakers are 50 inches tall and weigh in around 70 lbs. There is a 10.5 inch fullrange driver at the very top of the column firing forward. They sit on a plinth that is 12 inches square with a spike in each corner. They do not resonate. The box doesn't talk or rock. They play very loud. They are 101 db efficient. They seem to contradict much of what has been written here. I think the stability issue may be due to the fact that my driver cannot be seen to move, even at loud volumes because the excursion is very short. It seems logical to me that less pistonic excursion would be less apt to cause the box to move. As for resonance control, I don't know how they do it but there does not seem to be any cabinet activity at all.
All this leads me to conclude that mass is a substitute (and not necessarily an effective one)for innovative engineering.

Aha! Onhwy61 has offered a good explanation as to the workings of my speaker. They have a downward firing bass tunnel running the full height of the cabinet and the size of the aperture facing the floor is quite large. The freedom of the backwave to escape and the direction it goes would perhaps explain why the cabinet neither rocks nor vibrates.
My first post was written before his explanation appeared.

Macrojack, my explanation applies to both sealed and non-sealed speakers. A port, if appropriately designed, offers a controlled path for pressure to escape the speaker cabinet. Ported speakers still have to address cabinet flex. If I got it right, doesn't your speaker have a very slick multi-layer cabinet design. And since when did 70 lbs. become a light weight speaker?

Hwy-

I think you are correct about the cabinet but I am not sure.
I think 70 lbs. is light in comparison to the behemoths being mentioned here. And the things are over 4 feet tall besides.

The aperture at the bottom is about 4 inches by 9 inches. I don't know how it is configured inside but I would imagine an opening that large would present little resistance and therefore minimal pressure. Is that correct?