That's inexact. A real acoustic suspension woofer depends solely on the entrapped air in the enclosure. I don't know of any manufacturer building such designs nowadays. Acoustic Research in the 1970's was the major company marketing such speakers.
Altec Lansing, the defunct pro audio and theater loudspeaker manufacturer, released a real acoustic suspension woofer for home use in the 1970's. The cone of that 15 inch woofer when you put it on a table would just drop and touch the table top, as there was no stiff spider to hold it. Only the foam surround kept it fixed to the basket:
IIRC, today all sealed woofers have a stiffer spider, foam suspension has disappeared and drivers are built to withstand a lot more power than in the 1970's. I suggest that you peruse the posts which have been written above in this thread.
I knew I should not have jumped in here to try and clear up some of this nonsense. I should have known that if I did, that no matter how much effort and time I put into giving an explanation that was fully correct and derived from a reasonably good understanding of elementary physics and of the physics of loudspeakers, that some person would respond with something like "That's inexact", or similar B.S.
Given that you did that, I will repeat, and this time in bold:
The acoustic suspension principle applies to all speakers that use sealed enclosures.
That statement is absolutely, 100% true. I will try to explain to you why it is, but it ought to be obvious to anyone who would bother to stop and think about it for a minute or two before opining.
Now I will explain. It is simply this. In ANY speaker that is sealed, the air spring effect contributes appreciably to the total restoring force. I explained this fairly well in the first post I wrote above, which you either didn't read or didn't understand. So I'll try again and I'll try to keep it simple, using an example. Let us suppose that the driver's Vas is equal to the enclosure volume Vb. In this case the compliance of the suspension and the compliance of the air sealed in the enclosure will be equal. The point of expressing compliance as equivalent air volume is so that direct comparisons of this sort will be possible. So if Vas and Vb are equal, the total restoring force will be twice greater than it would be with either the suspension or the enclosure acting alone, and the two partial contributions to the restoring force will be equal. Hopefully you understand this and agree up to this point, but if not, then there isn't much point of us trying to have a dialog. Now, if the two partial contributions to the total restoring are equal, what are we able to infer about a speaker where this is true? Since Vas and Vb are equal, the ratio Vas/Vb will equal 1. As such, the following expression, which equates to the Vas/Vb ratio, will equal 1:
1 = (Qtc/Qts)^2 - 1
Now, you can hopefully see that in this case, the ratio Qtc/Qts will be equal to the square root of 2, approximately 1.414. If we make a reasonable assumption about Qtc, that it is half of the square root of 2, then Qts will be equal to 1/2. Thus, if Qts is equal to .5 and Qtc is equal to .7071, the suspension and the air in the enclosure will have the same compliance and will contribute equally to the total restoring force. Now of course you can get different results by using a different value for Qtc. If you make Qtc bigger, the enclosure becomes smaller, and the air spring effect becomes stronger relative to the suspension. You could also make Qtc smaller, in which case the balance would shift the other way. But .71 is a typical value for Qtc, so it is reasonable to say that in general, the air spring effect will contribute at least 50% of the total restoring force so long as Qts is not greater than .5.
Even though I tend to be very exact with what I say and was careful here with what I wrote, you responded by saying "That's inexact", then you wrote:
That's inexact. A real acoustic suspension woofer depends solely on the entrapped air in the enclosure.
At face value that is preposterous, because at face value it is not possible. You are claiming that in a "real" acoustic suspension speaker that somehow the suspension's natural spring effect disappears altogether. How exactly do you propose this happens? It does not happen. In fact, the dominance of the air spring effect, in any acoustic suspension speaker, applies only for low signal behavior. As the signal level increases and excursion increases along with it, the stiffness of the suspension increases more rapidly than the stiffness of the air in the enclosure. Eventually, at the extremes of excursion, the suspension becomes the dominant source of the restoring force, no matter how strongly the speaker adheres to the acoustic suspension principle.
Then you wrote:
I suggest that you peruse the posts which have been written above in this thread.
That's blatantly insolent. I'm tempted to tell you where you can kiss me, but I'm fighting off the urge to do that. In all of the posts in this thread, in response to Mr. Feinstein's article, there was just one that was informed and that provided meaningful insight into this question. It was of course the first the post I wrote, which you obviously did not read, because, most likely, it was beyond your technical comprehension. You actually believed that in an acoustic suspension speaker that 100% of the restoring force derives from the air spring effect. If you had thought about it for even half a minute you would have realized that this cannot possibly be true.
It is further untrue that a driver absolutely must have a high-compliance suspension in order for it to be useable for an acoustic suspension speaker (even a "true" one). This is a false notion that circulates in Internet forums like so many other false notions. If you earnestly study the matter you will realize that what this is all about is this ratio:
Which is equal to this:
Vas/Vb = (Qtc/Qts)^2 - 1
It is thus apparent that any two drivers that have the same Qts value (and for which Qtc in the speaker is the same) will adhere equally to the acoustic suspension principle. If you study Qts, Qes, and Qms, you will find that although a big value of compliance is a huge, huge benefit in achieving a low Qts value, that it isn't absolutely essential. It can be done, and it is done, with stiff suspensions, however the speaker will not be as efficient. The true difference in the old and the new is the difference in efficiency, yet when people on the forums start lamenting the loss of the highly compliant suspensions, they almost never mention efficiency. The reason they don't is because they don't have sufficient technical ability to figure out that you can have the same Vas/Vb as those earlier acoustic suspension speakers and that when you do the true differences are that the speaker built using newer, stiff drivers will not be as efficient (and the enclosures will be much smaller).
That said, there is also the related but separate question of deep bass extension. There is an inherent tradeoff between deep bass extension and adherence with the acoustic suspension principle. This has always been true. It is no different now from what it was fifty or sixty years ago. To adhere strongly to the acoustic suspension principle you need for Qts to be small. But the smaller the value of Qts, the greater the factor by which Fs is multiplied to obtain F3. Herein lies the real challenge of building acoustic suspension speakers. It is not especially difficult to build a midrange speaker or a mid-woofer speaker or even a conventional woofer speaker, adhering very closely to the acoustic suspension principle, because there are plenty of off-the-shelf drivers with adequately low Qts values, many below .2. Where it becomes difficult and challenging is with building a sealed subwoofer that will be flat in response right down to 20 Hz (or thereabouts) while at the same time adhering strongly to the acoustic suspension principle. This is a difficult thing to do, and this may well be more difficult today than it was fifty or sixty years ago, because it is more difficult to achieve a low value Fs without the benefit of a big value of Cms, the compliance.
Thus, if you want to lament the loss of high compliance drivers, and you want to do it in a way that will inform other people who understand this stuff that you also understand it, you should make the lament specifically about efficiency and about the difficulty in achieving a suitable low Fs value.