Why not acoustic suspension?

Modern’ish (vs. stuff from the 1970’s), but no longer manufactured - Aerial Acoustics LR5 (link).

thanks for the clarifications, so only my AR-2ax are acoustic suspension, all the others are simply sealed boxes.

my 15W woofers are the 1st column in this spec sheet from Electro-Voice. The last two columns, 15WK and 15BWK were the drivers used by Klipsch originally. 

file:///C:/Users/elliott/Downloads/15W,%2015BW,%2015WK,%2015BWK%20EDS.pdf

Manufacturers today:

Magico and YG acoustics are famously acoustic suspension. 

Sealed vs. Acoustic Suspension:

Well, that’s a new one on me.  There’s literally no way for a sealed box not to act as part of the spring mechanism unless the box is very large relative to the  Vas.   I guess I don’t know everything. 

It is 100% true though that before Henry Kloss the physics of the sealed box were not understood, and that his work caused an alteration in driver suspension design. 

So, perhaps this means, before AS was known, people might just put a driver in a box.  Still, unless the driver is very large, it would become part of the suspension, they just wouldn’t now how/why, or that the old stiff suspensions weren't very concerned with box volume.  In modern usage however I know of no normal speakers produced in a sealed box which are not acoustic suspension. 

Roll-off slope: 

Rolloff is affected by the Q, or tuning.  With an optimally flat acoustic suspension design, the roll-off is 12 db/octave.  However the size of the box matters.  Using too small a box can make the bass peak early, and roll off more sharply.  This can be useful for instance with a small speaker you want to give more bass.  Using too large an enclosure (and perhaps this is meant by "sealed") will roll-off earlier, more gradually and at a lower slope.  

It can be argued that with acoustic suspension there may not be much effective difference with different tuning, and that they are generally ~ 12 db/Octave.   If integrating with a subwoofer measurements and DSP/EQ capabilities are key to really knowing how to set things up. 

As always however, these are for the box in anechoic conditions.  The room, placement and "room gain" have a lot to do with what is actually perceived. 

Yes the air in a closed box affects the driver suspension. But it's only acoustic suspension if the air is more significant than the spider. When Edgar Vilchur designed his prototype he used a regular driver but cut away most of the spider so it no longer controlled the driver motion. Putting it in a small box allowed the air to bring back control. The claim was the air was more linear than the spider.

Closed box roll off is always ultimately 12 dB/octave. What varies is where roll off begins and the shape of the bass curve before hitting 12 dB. Poor design can cause a hump before roll off(any Q above 0,707). A good example is the BBC LS3/5a with a Q of 1.2. But the BBC did it to make it sound bassier than it would with a tight Q where the speaker would have sounded thin because the box resonance was so high. They sacrificed definition for bass balance.

I just learned something new.  I guess there’s a range of suspension / box configurations.  To me it’s all AS, but I guess in the formal sense, a true AS has to have a soft, compliant suspension.  

Modern speakers often have stiffer suspensions and while the air in the box is important in terms of the suspension it’s not as dominant. 

I stand corrected, my thanks and apologies.  I learned something new! 

Among the many differences of the modern sealed approach apparently is the reduced sensitivity to the box size.   This used to be a big deal.  

It's not UNIMPORTANT, but with the dominance of the driver suspension it can't hold as much sway as before.