Foam Plugs

It would be nice to know what size woofer you're talking about. The last drivers I shopped for were 10", and that's been a couple years ago. I couldn't buy the drivers that Lyngdorf used in their W210(raw) or anything equivalent, so I stopped shopping and stuck with my Nestorovics. Change the compliance(like by skeletonizing the spider) and/or moving mass, and you'll change the free air resonance(the Cms will change over time also). Lots of variables.

Rodman99999...The KLH driver was 12". I happen to know its Fs because I had to buy a replacement from KLH, and every driver was tested, and the Fs marked (to a tenth Hz) on the cone.

With a "real" AS driver you can bottom out the cone simply by handling it. It is an incomplete device without its enclosure. Perhaps the "loosest" driver I ever had was a Wharfedale 8" with flannel cloth surround. This was before the days of foam.

Eldartford, ""Sealed box" they may be, but not truly acoustic suspension." Agreed. That was the point of my initial post.

"A true "acoustic suspension" speaker system involves a woofer with a free air resonance of about 15 Hz." Disagree. A woofer designed to be used in an Acoustic Suspension alignment is not dependent on free air resonance, but the other parameters you and Rodman99999 have been discussing, along with a powerful motor structure. For example, it would be difficult to find an 8" or 10" woofer with an Fs of 15 Hz, yet a properly designed driver of this size could serve the intended AS purpose well.

Incidentally, Villchur's first designs used the silky material taken from the outside of mattresses, as he considered it the best thing he could get his hands on to implement his theories. Even though he felt it was crude, things worked out beautifully, and as they say, the rest was history.

Trelja...A low Fs is most definitely an essential element of acoustic suspension. (Not to be achieved by loading the cone with mass). To the extent that the cone compliance is tight (high Fs) its spring restraint is mechanical, not pneumatic. There will always be a mix of the two, but the more is pneumatic the better.

There are two main factors that when combined as in EBP = Fs/Qes.

If you have a low Fs (around 15 to 25) and you have a high Qes (expensive large motor light cone) then you will end up with a low EBP suited for a sealed enclosure (less than 50).

My subwoofer is sealed and uses Fs = 21 and Qes = 0.49 for a EBP of 42. It is a tight sounding (aka musical) subwoofer that sounds quite different from ported designs.

See this