turboyam
The Kenwood fan!
I agree too.
Dust cap sealing
- Thread starter harry398
- Start date
turboyam
The Kenwood fan!
This is why, if someone's to refoam a woofer, he really should not use shims (if not re-using the OEM dust caps). Some speaker repair shops sell dust caps.
If we change those, the design is compromised. Using more or less air tight dust caps OR paper ones, changes the woofer's compliance in box, sealed or B.R.
If we change those, the design is compromised. Using more or less air tight dust caps OR paper ones, changes the woofer's compliance in box, sealed or B.R.
spark1
Lunatic Member
Another question for those who say that the faster the rebound the better the seal; for the many - including me - who have reported slower rebound after sealing old surrounds, or making other changes to reduce leakage (such as new gaskets for the drivers and back plate), wouldn't we have to conclude that taking active steps to reduce leakage actually increases such leakage (as evidenced by the slower rebound)?
Again, I barely made it thru HS physics, and that was a long time ago. But I do know that after having done restorations on at least several dozen AR and KLH speakers with cloth surrounds, flattened gaskets, gaps around the backplates and even gaps in the cabinet joints, I've never seen the speed of rebound get FASTER after making changes intended to reduce air leakage.
Admittedly, I haven't always seen a big reduction, either...but usually at least some, and certainly never a noticeable increase.
Again, I barely made it thru HS physics, and that was a long time ago. But I do know that after having done restorations on at least several dozen AR and KLH speakers with cloth surrounds, flattened gaskets, gaps around the backplates and even gaps in the cabinet joints, I've never seen the speed of rebound get FASTER after making changes intended to reduce air leakage.
Admittedly, I haven't always seen a big reduction, either...but usually at least some, and certainly never a noticeable increase.
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spark1
Lunatic Member
I would think that if the replacements are of similar construction, the change would be very small and unlikely to be audible. It would be interesting to see measurements showing the amount of change when going from mesh to solid, and vise versa (as a "worst case"). Do you know of anyone who's done such measurements?
Personally, I prefer shimming when replacing surrounds...especially on drivers with very fine gaps. But I generally re-install the original dust caps, unless previously damaged.
woodj
Super Member
If the cabinet was totally, perfectly sealed, even though air is compressible, it would difficult at best to push the cone in without damaging it; even if you could, the distance it could be pushed in and the travel distance during operation would be less than optimal.
spark1
Lunatic Member
Here is an interesting and informative thread on the topic of woofer rebound in an acoustic suspension speaker:
http://www.classicspeakerpages.net/IP.Board/index.php?/topic/4630-ar-box-and-woofer-sealing/
There is a reference to Roy Allison as the progenitor of the slow rebound test (vs Vilchur). Two other things I gleaned:
1. The smaller the woofer, the less useful this "test".
2. Further verification of the fact that some small amount of leakage is indeed required for proper operation, as Vilchur originally described in his patent.
http://www.classicspeakerpages.net/IP.Board/index.php?/topic/4630-ar-box-and-woofer-sealing/
There is a reference to Roy Allison as the progenitor of the slow rebound test (vs Vilchur). Two other things I gleaned:
1. The smaller the woofer, the less useful this "test".
2. Further verification of the fact that some small amount of leakage is indeed required for proper operation, as Vilchur originally described in his patent.
spark1
Lunatic Member
Yes.
And of course, even with some leakage, there is still a pressure change corresponding to cone movement.
The other thing to keep in mind is that we are not talking about dramatic differences in bass response until you either get it TOO sealed up, or have gross levels of leakage. Assuming a cabinet that has the same leakage as when it came off the assembly line, compared to that same speaker without sealant on the surrounds, the difference in bass response will be relatively small if I understand the variables properly. Personally, I am more concerned with adding weight or stiffness to the surrounds by putting on too much sealant. This apparently results in a more significant loss in bass performance.
363watt
New Member
Really like all the conversation on the subject.
I have performed a number of tests tonight on the surround surface of many of my drivers. I used a mityvac automotive tool touching the surface squarely.
The ones that give a reasonably slow return developed and even held some vacuum and the ones that have fast return did not.
These surrounds are porous and will not perform as originally designed in these sealed cabinets.
One of the suppliers I contacted seemed like they have not heard of this. One offered a treatment for me to try.
I want to share my research so others can make a decision before spending their money and time refoaming speakers.
More to come.
See videos
Leaker
sealed
I have performed a number of tests tonight on the surround surface of many of my drivers. I used a mityvac automotive tool touching the surface squarely.
The ones that give a reasonably slow return developed and even held some vacuum and the ones that have fast return did not.
These surrounds are porous and will not perform as originally designed in these sealed cabinets.
One of the suppliers I contacted seemed like they have not heard of this. One offered a treatment for me to try.
I want to share my research so others can make a decision before spending their money and time refoaming speakers.
More to come.
See videos
Leaker
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woodj
Super Member
Cool stuff.
StimpyWan
Addicted Member
I believe all of the AR woofers that I've refoamed, had an inner and an outer dust cap. The inner dust cap was a flat cardboard disc, glued directly to the top of the voice coil, and the woofer junction. This sealed the gap. The outer mesh dust cap was for cosmetic purposes only. It didn't require any sealant.
363watt
New Member
The 8 and 10 inch woofers have that cardboard cap you speak of but I’ve yet to see it on the 12 inch AR woofer.
These should be considered the two primary sources of the non-sealed result.
Porous dust cap and foam surround.
It has been hit or miss with the suppliers of foam surround for me in my experience.
These should be considered the two primary sources of the non-sealed result.
Porous dust cap and foam surround.
It has been hit or miss with the suppliers of foam surround for me in my experience.
Air suspension woofers have a much looser suspension using the air pressure in the cab as a spring, and to help prevent bottoming out the VC. Read any papers by Vilcher on the acoustic design cab and woofer, it's all explained there. There is suppose to be a very slight amount of air leakage by design, but a properly sealed cab and woofer will result in the slow return to neutral when pushed in as it should.
From discussions I've had with Roy C. the surrounds on vintage woofers rarely need resealing, and never the dust caps. The only woofers I applied a very thin coat to were my 4x woofers, and noticed an improvement in bass response. KLH woofers did seal the dust caps at the factory. Look at any KLH vintage woofer, and you can clearly see the sealer brush strokes. I apply sealer to both the surrounds and dust caps on KLH woofers, which is described in that factory bulletin.
Glenn
From discussions I've had with Roy C. the surrounds on vintage woofers rarely need resealing, and never the dust caps. The only woofers I applied a very thin coat to were my 4x woofers, and noticed an improvement in bass response. KLH woofers did seal the dust caps at the factory. Look at any KLH vintage woofer, and you can clearly see the sealer brush strokes. I apply sealer to both the surrounds and dust caps on KLH woofers, which is described in that factory bulletin.
Glenn
harry398
Active Member
HI Glenn
The 2 issues are the dust cap seal and even more problematic inferior "new" purous surrounds sold
363watt shows vividly the obvious problem. POROUS SURROUNDS.
I agree with the slow movement you describe with the cloth surrounds, this is also true with other surrounds, otherwise there is no Suspension effect. We are not talking 90psi seals, as some people are thinking.
I have had OK results from 2 suppliers so far, 1 is just unsatisfactory and I am waiting for their response. I will not reveal them until I give them a chance to make this right. Another example of a bean counter/cheater without regard for quality.
harry398
Active Member
a little update.
After revisiting some of my inventory and their surrounds.....I am finding the Midwest speaker foams are leakers. I have sealed the dust caps and the surrounds just dont seal.
I have recently tried a few sets from Rick Cobb......excellent seal. Like a good cloth surround woofer.
I revisted an AR3a woofer I refoamed with Geoaliwil........excellent seal.
I have a few Poly AR speakers I refoamed with Geoaliwil foams.......excellent seal.
I have ON order a set from Springfield speaker.....
I am very disapointed with Midwest speaker foams, and especially their customer service.
There is alot of work involved in doing these, and having porous surrounds , doesnt make me happy.
After revisiting some of my inventory and their surrounds.....I am finding the Midwest speaker foams are leakers. I have sealed the dust caps and the surrounds just dont seal.
I have recently tried a few sets from Rick Cobb......excellent seal. Like a good cloth surround woofer.
I revisted an AR3a woofer I refoamed with Geoaliwil........excellent seal.
I have a few Poly AR speakers I refoamed with Geoaliwil foams.......excellent seal.
I have ON order a set from Springfield speaker.....
I am very disapointed with Midwest speaker foams, and especially their customer service.
There is alot of work involved in doing these, and having porous surrounds , doesnt make me happy.
Agree as well. You are compressing air in a sealed chamber, should push it right back quickly, much as squeezing a balloon.
363watt
New Member
Update
I used a pair Cobb surrounds to refoam a set of 8" and 12" AR woofers today. I know I know 11"........LOL Dark Charcoal Boston Acoustic fillet style.It developed good vacuum using the mityvac so I went forward with the install.
With the dust cap off the return was instant, after taping a cap in place, presto. slow return.
I have had good success with now Cobb, prior Geowili and 1 pair using Springfield's on a set of Snell bookshelf speakers, but Midwest has under performed especially in the 8" and 10" surrounds. He sent me a bottle of surround sealer which corrected only one pair of 8" surrounds, 4 other 10" and 2X 8" and 2X 12" would not seal.
I am replacing these slowly with Cobb surrounds and may give Springfield some business two after Harry398 reports back.
I used a pair Cobb surrounds to refoam a set of 8" and 12" AR woofers today. I know I know 11"........LOL Dark Charcoal Boston Acoustic fillet style.It developed good vacuum using the mityvac so I went forward with the install.
With the dust cap off the return was instant, after taping a cap in place, presto. slow return.
I have had good success with now Cobb, prior Geowili and 1 pair using Springfield's on a set of Snell bookshelf speakers, but Midwest has under performed especially in the 8" and 10" surrounds. He sent me a bottle of surround sealer which corrected only one pair of 8" surrounds, 4 other 10" and 2X 8" and 2X 12" would not seal.
I am replacing these slowly with Cobb surrounds and may give Springfield some business two after Harry398 reports back.
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spark1
Lunatic Member
So you are taking the position that Vilchur and Allison were wrong (the guy who patented the design, and his chief design engineer)?
The box is NOT sealed...rather, it is very slightly porous (as specified in the patent application). By slowly pushing the cone in, you are forcing air out. The slow rebound indicates proper seal (which, again, is NOT airtight) as outside air slowly replaces what was pushed out. If the cabinet has too much leak, it rebounds quickly because the outside air can be more quickly drawn in to balance the interior and exterior pressure.
As another contributor pointed out, the box cannot be completely airtight, as doing so would make woofer incursion nearly impossible.
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363watt
New Member
I never said they were wrong, Great design!
I have owned and worked on over 30 pairs of AR and and other acoustic suspension (sealed) speakers. Many of them from new. This was the way they functioned from the factory all the way up until the foam rotted. KLH had a bulletin to recoat woofer surrounds with butyl for sealing porous cloth surrounds. I mean why do speaker drivers have gaskets and crossover boards glued and stapled?
My videos clearly show the proper responses from this type of system. Don’t take my word, go and see for yourself. Definitive technology, JL audio, infinity to name a few all use this same principle in their sealed systems and perform the same way. Slow in and slow release.
An open mind gains knowledge..........
I have owned and worked on over 30 pairs of AR and and other acoustic suspension (sealed) speakers. Many of them from new. This was the way they functioned from the factory all the way up until the foam rotted. KLH had a bulletin to recoat woofer surrounds with butyl for sealing porous cloth surrounds. I mean why do speaker drivers have gaskets and crossover boards glued and stapled?
My videos clearly show the proper responses from this type of system. Don’t take my word, go and see for yourself. Definitive technology, JL audio, infinity to name a few all use this same principle in their sealed systems and perform the same way. Slow in and slow release.
An open mind gains knowledge..........
spark1
Lunatic Member
Did you read my post? It was in response to the post by nfafan, in which he states his agreement that fast rebound indicates proper amount of seal. That's why his post is quoted in my response.
And yes, an open mind gains knowledge. So does careful reading. I don't need to take your word, or look at your videos. I've worked on quite a few more than 30 pairs of speakers (although that in itself proves nothing), including all of the "classic" AR and KLH speakers other than the AR1 and the KLH Nine.
As for the KLH documentation; you might note that I am the one who posted it in this thread. Not sure how any of this relates to how crossover boards are mounted.
And yes, an open mind gains knowledge. So does careful reading. I don't need to take your word, or look at your videos. I've worked on quite a few more than 30 pairs of speakers (although that in itself proves nothing), including all of the "classic" AR and KLH speakers other than the AR1 and the KLH Nine.
As for the KLH documentation; you might note that I am the one who posted it in this thread. Not sure how any of this relates to how crossover boards are mounted.
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Get a grip. I was agreeing with the other post; squeeze a full balloon - a sealed chamber - and see how it bounces back. Squeeze a porous - non sealed - chamber - slow or no bounce back. That's all there is to my post.
Did they or did they not create a "sealed chamber" - ie air tight as the word sealed implies?
Anyway, who cares, does it sound good - that's all that matters.
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