Bloated speakers/weight wise

By itself a speaker's weight means little, but in the context of an overall design it can quite useful. The problem involves lowering the sonic contribution of the speaker cabinet, which at some frequencies can amount to 40% of the overall sound emitted by the speaker (I saw that measurement in an old Stereophile). The easiest way to limit the cabinet's output is to make it massive and less likely to be sympathetically excited. There are other ways to make the cabinet highly rigid and inflexible, but they are expensive (contrained layer, exotic materials, etc.). As a practical matter if you want low distortion, high volume and deep bass your speaker will have to be solidly built which equates to high mass. That could mean 30 to 50 pounds for some speakers and 200 to 500 for others.

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?

Zaikesman, I agree that it is more complicated than my earlier post presented, but I don't think I'm incorrect in stating that adding mass is the easiest and cheapest way to deal with cabinet vibration. It's not a perfect solution, but it does work fairly well. Going from 1/2 inch to 3/4 inch MDF or doubling up layers of MDF (or plywood) is a tried and true method to increase cabinet rigidity. There are better ways to achieve the same end like CNC milled aluminum, carbon fiber layers, concrete over wood, or even the interlocking jigsaw pieces as used by Sonus Faber. You could also take a completely different course and go for a cabinet thats extremely light yet sufficiently rigid with the goal being a very quick dissipation of the drivers' backwave energy. Any of the alternative methods is more costly than the somewhat unsophisticated approach of adding mass. It's a brute force approach to solving a problem, but that doesn't mean it's ineffective. Again, as I stated earlier, adding mass has to be part of an overall speaker design concept. Used in an non-optimal context adding mass has little positive impact.

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.