If the plugs are closed cell foam; the alignment becomes an acoustic suspension. If the foam is somewhat open; it will serve to partially damp the port's output.If your speaker's placement was say, closer to the corners of the room; they could serve to reduce any boominess that resulted.
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Basically, if you got to put your speakers near the wall or corners, then you'll probably need the "foam plug" to help tame the bass "boominess". Of course, there is a part of me that ask the question "why don't they make acoustic supension speakers anymore?". Seems to me, that you didn't have near the issues with speakers placement, back when "acoustic suspension" speakers were the norm.
Rodman99999, "If the plugs are closed cell foam; the alignment becomes an acoustic suspension."
Maybe, but probably not. What you have is more or less a sealed box alignment. Acoustic Suspension is more specific than that, and requires certain parameters be met. Not that the ingredients involved in implementing bass reflex and Acoustic Suspension designs are mutually exclusive, but in my opinion, it's difficult to have both bases covered. I'm confident you know the differences based on our prior discussions, but just want to make sure there is no confusion on the part of those reading here.
I agree with your statement on the reason the plugs would be supplied. However, I remain dubious as to whether a design that was presumably optimized with a bass reflex alignment would not be facing a one step forward, three steps back situation with the plugs installed.
Then again, given that many who design loudspeakers today are more possessing in cabinetry/veneering ability than the requisite mathematics and engineering involved in loudspeaker design, the assertion I made about "presumably optimized" bass reflex alignment (some would argue there is no such thing) might be asking far more more than said folks are capable of.
Mr T- Yes, I do understand your point. However, most make no distinctions between sealed box and 2nd order/acoustic suspension designs nowdays. ie: This site moves directly from a 2nd order alignment(calling it variously, "2nd Order", "Acoustic Suspension" and "Sealed Enclosure"), to a 4th order alignment: (http://www.danmarx.org/audioinnovation/theories.html) I do agree that IF the woofer and enclosure were optimized as a 4th order alignment, it would not be optimized as a 2nd order, with the vent sealed. BUT- the woofer would still be operating with the enclosure volume acting as an air spring(acoustic suspension). Actually- Villchur came up with the "Acoustic Suspension" design around 1954, and started building speakers with Henry Kloss, somewhat before A. N. Thiele published anything concerning speaker parameters, or cabinet alignments(around 1961), so things could actually get (somewhat)"optimized."
Rodman99999, "However, most make no distinctions between sealed box and 2nd order/acoustic suspension designs nowdays." That solidifies my feeling regarding the dumbing down of the craft over the past decade-plus.
Beyond that, thank you for your explanation.
Sadly, it seems as if cabinetry occupies the lion's share of loudspeaker design today. If one ever saw his own personal loudspeakers, they would guess that Bud Fried must be turning over in his grave right now.
I take a more skeptical view of how successful a woofer designed to be used in a vented alignment would do in Acoustic Suspension duties as their responsibilities are far more different than the average Joe understands. Claw and upholstery hammers both drive nails, yet clearly serve very different functions, as do Acoustic Suspension woofers and those to be used in bass reflex cabinets. People trivialize this these days, due to a lack of understanding and familiarity. The (low - mid power) tube renaissance brought along with it the need for maximum loudspeaker efficiency, which usually means bass reflex speakers. Now, the pendulum has swung too far the other way, and folks are missing out on the advantages Acoustic Suspsension brings to the table.
Anecdotally, a friend of mine, whose loudspeaker ports (made of cork) deteriorated to a great degree over the years, and then replaced them, experimented with stuffing them. He was not at all happy with the results, and soon removed the material, never to go back. That put a real bad taste in his mouth about sealed speakers in general. To me, it was not surprising, as the Focal made woofers in his speakers were simply not designed to be used in that application.
Finally, the Acoustic Suspsension alignment is probably the greatest post war advance in high-end audio. Most agree it was the very thing that brought (en masse) stereo sound reproduction into the home. Think about it, would we all be still listening in mono otherwise? Like most implementations of genius, it was amazingly simple. As you know, Villchur had no desire to manufacture a loudspeaker, he simply wanted to sell the idea to a company in the business, and make a few bucks in the process. To put it politely but literally, he was laughed out of every room he presented his idea. I admire the spirit and determination of a man who answers this type of rejection with building one of the most successful high-end audio companies ever ala implementing his vision.
A true "acoustic suspension" speaker system involves a woofer with a free air resonance of about 15 Hz. My KLH12s were 14 Hz. You can't find a driver like that today. Evidently speaker system designers today just don't trust that trapped air creates a spring. A spring more nearly linear than any driver's compliance.
"Sealed box" they may be, but not truly acoustic suspension.
Mr T- They laughed at Bob Fulton too, when he'd walk into a shoppe with his 'Gold's'. The laughing stopped, when the music started. Look at the revolution in cables he started. Mr E- There are a few drivers available, with fairly long throw voice coils and wide surrounds. If one were really intent on loosening the compliance more for a true Acoustic Suspension design; they could do what Villchur did, and cut away most of the spider(leaving just enough to keep the VC aligned in the gap).
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.
Eldartford, "no pontification." Do you have something against us Catholics?
Seriously, though, what I mean is that your statement, "A true "acoustic suspension" speaker system involves a woofer with a free air resonance of about 15 Hz" is incorrect. It really is as simple as that.
AS woofers were not always 12". They were often 8" or 10", with an Fs of 25 - 40 Hz. While certainly not high, not the 15 Hz you stated as being a requirement, either. Fs in and of itself was not what made the driver suited to the task - or not. Instead it was some of the other things you mentioned.
Trelja...I concede that the Fs of 14 or 15 is what I would expect for a 12" or 15" AS driver. 10" or 8" would be higher, which is perhaps why such drivers are less successful as AS drivers.
Note that my point is not that you can't achieve a rational sealed box alignment with a tight driver, but rather that the linear quality of the cone spring is degraded, affecting distortion, about which T/S has little to say.
My affection for acoustic suspension goes back to the AR1. This was a woofer-only box. The better-known AR2 was created by adding a tweeter.
Pontification is not unique to Catholics. In fact it refers to people who are not the holy father talking as if they were.
HSU ported subs currently are double ported. They also come with a single foam plug. You run the sub in 'Max Extension' or 'Max Output' mode, depending on plug insertion or not. There is also a backpanel switch to be set according to the plug insertion condition.
I have never experimented with this, since even in Max Extension mode, it goes plenty loud enough, even in a room which is on the large side for the sub.
The plug is not intended to 'convert' the sub to true AS, but just vary port tuning, as near as I can 'figger.