09-11-12: Dhl93449
JohnnyB
Your are describing the properties of a driver optimized for a AS design. The OP does not have that. He has a ported design he wishes to convert with a plug. I only mentioned that he can get SOME of the benefits of the AS design (not all of them) by plugging his ports. He will also give up some of the low end frequency response he gets with a ported design.
Telling him to buy another speaker entirely is not that helpful IMHO.
I never told him to do any such thing. I was addressing Dhl93449's assertion that acoustic suspension and sealed enclosures are the same thing. They are not. I *know* the OP has a ported enclosure. Acoustic suspension isn't really any part of the OP's discussion. But plugging the ports changes the damping, causes the bass rolloff to happen at a higher frequency, *but* makes the rolloff occur at a gentler slope. I'm all for him trying it. I was just trying to address the misconception that sealing the enclosure turns the sub into an acoustic suspension design. It does not; but it turns it into a sealed enclosure, or at least raises the damping significantly. |
Dhl93449... For true AS the driver must be quite specialized, and completely useless in a ported enclosure.
Just curious, but have you ever held in your hand a 10inch driver with free air resonance of 13 Hz? Such were in my KLH12 and KLH5 systems. Question 2... can you find such a driver on the market today? |
JohnnyB
Your are describing the properties of a driver optimized for a AS design. The OP does not have that. He has a ported design he wishes to convert with a plug. I only mentioned that he can get SOME of the benefits of the AS design (not all of them) by plugging his ports. He will also give up some of the low end frequency response he gets with a ported design.
Telling him to buy another speaker entirely is not that helpful IMHO.
There are numerous manufacturers (like B&W for example) that supply port plugs for their vented speakers. No one says this will convert their ported cabinets to an optimized AS design, but it may provide benefits. I myself do this to tighten overall bass response when using my HSU sub (which is also sealed) and adjust the crossover to compensate for the higher CP of the plugged B&Ws.
You can also find numerous speaker design guides that mention the use of the same driver in either AS or ported cabinets. Does not mean that using these mulipurpose drivers in a sealed cabinet is a bad thing. The driver does not have to optimized for AS to be called AS. That's nitpicking. |
To Johnyb53 and Eldarford, I have Harbeth and Spendor LS3/5 type two way monitors with sealed woofers. The bass reminds me of the older AS speakers from years ago. Are these considered AS?
Thanks
Yogiboy |
I am old enough to remember when AR came out with their first speaker, which was the AR1...just a woofer. Then they added a high end driver, and the AR2 was born. It blew away every other speaker on the market.
Maybe it is time for acoustic suspension to be reborn. Most present-day audiophiles have never heard true AS, and their reaction might be similar to what happened back in the day. |
Sorry Dhl93449, Eldartford had it right: An air suspension design requires a sealed enclosure, but not all sealed enclosure speaker designs are air suspension designs. The bass drivers made today usually come with the specs to determine the enclosure volume and port length and diameter for a ported speaker and the enclosure size for a sealed design. The sealed design is *not* an acoustic suspension design because the woofer's ability to make excursions and return to neutral is entirely dependent on the cone stiffness and magnet strength. In a true acoustic suspension speaker, the speaker cone and magnet strength are significantly reduced along with the enclosure size. The sealed air in the enclosure then supplements the magnet and suspension to control cone motion. In a standard sealed enclosure, which is much larger relative to the woofer diameter, the sealed air does not significantly contribute to the cone excursion and restoration. For example, a standard 10" woofer today might require a 4.8 cu. ft. enclosure if sealed. However, the true acoustic suspension designs of the '60s (e.g., AR3a, KLH, Advent, etc.) were mounted in a 2.3 cu. ft. enclosure and produced true low-distortion bass down to around 30-33 Hz. The floppy suspension and thin cone lowered the free air resonance of the woofer to make this possible. |
I obtained some makeshift plugs for the ports on my B&W 803's at Wallymart, kids section. Those closed cell foam play balls work great. Just measure your port diameter and look for foam balls that are a bit larger. If you get a reasonably tight fit, they will seal air tight and that is what matters.
And I would not use a foam tube as you can make annoying wooshing port noise from the smaller diameter opening.
An air suspension design just means the driver is mounted in a sealed cabinet, ie, no ports. While the optimized cabinet design for an air suspension (dimensions, volume, etc) will be different than a ported design, plugging the ports on a ported design will get you some of the benefits of the AS design at the expense of low frequency response. |
Aewhistory... If you google "acoustic suspension" you will find good info.
The acoustic suspension concept is to replace the mechanical springiness of a cone speaker with the springiness of air trapped in a closed enclosure. It requires a speaker with cone free air resonance on the order of 12 to 14 Hz. (Hold one in your hand and it flops around like a dead fish). Such a driver cannot be used with other types of enclosure. Few if any drivers are made today with suitable characteristics. Low distortion is the primary benefit, but a significant secondary benefit is that the appropriate enclosure size is relatively small. |
Thanks for all the replies!
Hey Johnny, good idea. I want to say that my SVSs did come with a plug eons ago, but I've lost them and, anyway, I'd need three for each. These are the earliest SVS cylinder subs; they may not make anything like this any longer, I don't really know. Still worth checking.
Rrog, interesting idea, although if you're referring to my subs' size, they're not small. I think the newest generations of SVS have gone the mighty mouse approach, but back when I bought they were making subs that made their buyers look like they were compensating for something (no.... The answer is no, I am not compensating... :)
But seriously, I've got the tallest of the passive cylinders from 2002. I think the model was something like 12-46cs ( they are the tall ones, so I might have the height number wrong or something). Anyway, these are big mombajombas; too big for the room they are in now. I am going to be selling one and, depending on how the stuffin' works maybe both.
Zman, Rod: thanks for the leads and ideas. I will look into those ideas. Definitely worth it.
Eldart: I feel like we are talking about the same thing tho, no? To be honest tho, I've never seen a sub advertised as an "acoustic suspension" type. I've seen ported, sealed, different kinds of loadings (or maybe the right nomenclature is different order subs?). Could you point me toward info on acoustic suspension? Thanks! |
Why don't you call SVS and see if they'll send or sell you a plug? Your model may not have come with one, but all their ported square subs come with foam plugs now to adjust the bass rolloff profile. |
You can also stuff the port with drinking straws. It's tedious, but it can be done. However, fighting a component to this extreme usually means its days are numbered. These small subwoofers require high power and heavy EQing to reach their maximum performance. |
Bonded Dacron(http://www.foambymail.com/DACRON/polyester-fiberfill.html)(http://www.ebay.com/itm/27-Wide-Bonded-Dacron-Batting-SOLD-PER-YARD-/390104452113?pt=LH_DefaultDomain_0&hash=item5ad4098c11)works great for damping ports. You can roll it as tightly or loosely as you desire, which will enable you to tune the port to your taste. The stuff is available at most fabric shops. |
You can go to Lowes or HD and get some pipe insulation that fits the size of your port.
It's made out of neoprene with a hole in the center.
It will give you a smaller port and controle excess blume with the bass. Hope this helps. John |
What you want is an "acoustic suspension" subwoofer. This is NOT the same as a "sealed" subwoofer, and even less a ported unit with the port pluged. |
