Should woofer dust caps leak air?

[Guest]

I had my AR3a woofers reconed when I first pulled them out of my neighbor's trash. Recently, while trying out replacement driver options (I know, I know...), I was very careful to maintain (restore, actually) the acoustic seal around the tweets and mids I was trying out, with the understanding that the seal is critical to the bass response of these speakers. However, even after getting a perfect seal around the tweeters and mids, I noticed that the woofer cones didn't seem tight when gently pushed in and released, and further investigation revealed that the dust caps on the woofers are made of a loosely woven material that I can actually see through, and that lets air through (if I get close enough, I can feel a breeze from the dust cap area when pushing in the cone).

Is this normal? If not, what can be done about it? Replacement of the dust cap? Treating of the cap? Re-coning again?

Thanks for all the help!

--Daniel

[ninohernes]

No they shouldn’t. Call Layne Audio [615] 298-4124 and buy a bottle of their woofer cone surround sealer. This stuff is like magic! I coated the surrounds and cones of my AR-2 and AR-3 woofers. They are so airtight, its almost impossible to move them in and out (once installed in the cabinet) the bass response is tight and controlled now.

Joe

[Guest]

Is the sealer similar to "Wet Look For One" from Parts Express (go to partsexpress.com, search for part #340-522)?

Any idea why *any* dust cap wouldn't be made of an air-impermeable material in the first place?

Thanks for the help!

--Daniel

[Guest]

I checked with tech support at Parts Express on this, and there appears to be a specific term for the part in question: a 'venting-type dust cap'. Dunno when such a thing would be appropriate, but a sealed box would seem to be the wrong place for it...

They said not to use the Wet Look sealer on the cap, but I think they're concerned that it would mess up the function of the driver if it was *supposed* to have a venting-type cap.

--Daniel

[Guest]

More on this from Parts Express. Here's what they say about the venting dust cap sealing issue:

"The venting dust cap should not allow a significant amount of air to escape from the cabinet. Air will mostly breathe in and out from around the voice coil former area as the cone moves in and out, as a way to cool it. You've probably heard of a 'vented pole piece'? It's another (more common) way of doing the same thing, but the vent

is an opening in the back center of the driver structure. Neither will negatively affect your air suspension speakers."

Does this sound right? I would think that letting air enter the cabinet through the dustcap would destroy the function of a sealed box, by definition.

Opinions?

--Daniel

[Guest]

I was told the same thing by the guy that did the re-foaming on my 11" woofers for my AR TSW-910's. They look like impermeable plastic from the outside, but yes, they do vent. I think maybe to help cool the voice coil. I can assure you I have no lost bass response in those monsters! If you had a "perfectly" sealed box, I think it may be more detrimental to the structure of the woofer as it's drawn back into the cabinet to produce bass, and subsequent distortion of the cone itself would result. The vented cap may also act as an pressure "equalizer" of sorts.

I understand your concern, but I'm sure the engineers that designed your speakers calculated for it. I have small leaks in my sub boxes in my Mustang due to hole size, box carpet, etc. and I can also assure you that 20 Hz signals are reproduced effortlessly. I wouldn't sweat it too much, unless you have bullet holes or some idiot ported the speakers, you're ok. Do your speakers sound good in the bass region?

Chris

[Guest]

My impression is that the performance of an acoustic suspension loudspeaker relied rather heavily on the seal -- the trapped air acts as a spring, or suspension, for the woofer cone, etc. I would think that having a significant leak in this seal could be quite damaging to this system, potentially producing a damping, rather than an energy-returning, effect on woofer cone motion. As for the engineers who designed the loudspeaker knowing what they were doing, remember that this vented dust cap was installed by a speaker repair shop, not by AR at manufacture!

Any enclosure gurus (Ken, Tom, etc.) want to weigh in? I'm leaning towards sealing the dust cap if I can ever get hold of Stephen Tidwell at Layne.

--Daniel

[kkantor]

1- No AR woofer I know of used any kind of purposeful venting on the dustcap.

2- Such schemes are substantially irrelevant to cooling, (as are most vented pole pieces). But they may have other, more legit, functions. For example, changing the hf response of the driver.

3- Restoring a driver is one thing. Improving it is another. To do the later requires a clear plan. The minute you start randomly tweaking speaker drivers with goops, you are on your own... you change moving mass, you change bond termination, breakup modes, on and on. Believe me, if it were possible to make a driver better by gooping it, that would have been done by AR in the first place.

4- Minor air leaks are not a big problem, unless they hiss or chuff or whistle. In terms of bass response, an air leak in a sealed box adds a first order high pass filter which can be estimated as follows:

Gently push in the driver to a comfortable point, using evenly applied pressure around the cone (eg- several fingers). Let the cone go and estimate the amount of time it takes to return to the rest position. Roughly, the frequency of rolloff caused by the leak is 1/t. In other words, if the driver takes .5 seconds to snap back, the 6 dB rolloff starts at 2 Hz. (This fault reduces the bass by about .05 dB at 20 Hz.) If the driver takes 2 seconds to stop moving, the corner frequency is 4 times lower yet.

5- A perfectly sealed box would be a barometer. Not a good plan, but likewise not really possible.

Ken Kantor

www.intelligentaudiosystems.com

[Guest]

Daniel:

I saw no mention of a repair shop in any of your previous posts. Where did I miss it?

Chris

[Guest]

Chris -

Im my first post I stated that I'd had the woofers in question re-coned.

Best --

--Daniel

[Guest]

The short answer is: I dunno.

The longer answer is that the replacement drivers 11/12" from ABTech do not have a "venting" dustcap so far as I can tell.

My now very well vented (where the surround used to be) original drivers in my 9s aren't, as far as I can tell, leaky.

Does it matter? I'd say Mr. Kantor has a far better idea than I do about that and he seems to say, "Not much, if at all," as I understand his reply.

Qualifying my reply: I'm so worried about "imperfections" in a recone or re-surround job that I'm spending the $650 to replace the drivers rather than resurround them. I know "new" and "perfect" aren't synonomous but I calculate I stand a better chance of getting "closer to perfect" with new drivers than with even professionally resurrounded ones.

But I'm with you on the "common sense" angle. If they were meant to breathe AR would have breathed them. In an "acoustic suspension" speaker where air leaks are critical enough that someone takes a stethoscope to the mounting screws to be SURE they aren't leaking it defies logic that there would be a purposefully-put hole in the middle of the only driver in a 3a that uses the sealed box.

Wouldn't that be "acoustic semi-suspension" or something?

Bret

[Guest Barrydor]

>Qualifying my reply: I'm so worried about "imperfections" in

>a recone or re-surround job that I'm spending the $650 to

>replace the drivers rather than resurround them. I know

>"new" and "perfect" aren't synonomous but I calculate I

>stand a better chance of getting "closer to perfect" with

>new drivers than with even professionally resurrounded ones.

>

I need to respectfully disagree with you here, Brett. That logic only applies if you are certain that the replacements are identical to the original units.

I have read that some of the replacement woofers being offered are later units manufactured in Japan. They are slightly less compliant than the originals. This can and will alter the bass character of the AR9.

I would not underestimate the value of restoring the original drivers. Replacing a surround is not rocket science. A shop with a reasonable degree of skill and care can do a fine and reliable job.

Barry

[Guest]

>I need to respectfully disagree with you here, Brett.<

I'm "casual" about discussions,so dis-respectfully disagreeing would have been okay, too. ;-)

I understand and agree with all facts / assumptions you present. I disagree with your conclusions, however.

I don't see that there is a nickle's worth of potential difference between a refoamed speaker (non-original surround materials, non-original adhesives) and a "replacement" new driver made 25 years later.

Except - I won't worry that the adhesive was applied incorrectly or that the surround is off-center. . . as much, with a new driver.

I understood that ABTech was getting their drivers for AR replacements from the same company that manufactured the the drivers for these speakers in the first place. Not true?

I'd be interested in learning what you know about any differences in the replacement drivers. Can you point me somewhere to read-up on them for myself?

Bret

[Guest Barrydor]

>I understood that ABTech was getting their drivers for AR

>replacements from the same company that manufactured the the

>drivers for these speakers in the first place. Not true?

Not true

>I'd be interested in learning what you know about any

>differences in the replacement drivers. Can you point me

>somewhere to read-up on them for myself?

See the thread on pp.3 of this forum entitled "Re-foaming the AR-9" for clarification. In particular, see reply #6, written by Tom Tyson

Barry

[Guest]

>See the thread on pp.3 of this forum entitled <

Done.

So I get more durability in the replacements and give-up some low frequency extension without distortion.

But nobody has heard the difference, or at least nobody mentioned it.

I could swear that I read somewhere that the company that is producing the replacement AR parts is the same facility (if not corporate ownership) that has built AR drivers for some time. In fact, I read, it builds a lot of drivers for a lot of companies.

I'll have to see if I can find where I ran across that.

Okay, I'm game. Maybe I should send my old drivers to PA to be resurrounded after I get the replacements in the cabinets. Why not? Like a mountain, it's there.

Bret

[Guest]

Boy oh Boy oh Boy !

A wise man once said to me, "There's no use arguing with a man when he's right," and were you ever right.

I'm going to post a message with images of the original 8" driver (sans surround) next to the replacement driver.

Not only was I misinformed, I was so wrong it isn't even funny.

Bret

[Guest Barrydor]

What do you mean? Do the new units differ substantially in appearance from the originals? What about the new woofers?

Barry

[Guest]

>Do the new units differ substantially in appearance from the originals? What about the new woofers?<

Barry, I tried to cover this in another thread, but that thread isn't showing-up so I'll answer you here.

First and most importantly the 8" drivers from ABTech are not the soft, fuzzy paper cones of the originals. They are either some form of carbon fiber or poly or plastisized paper. They appear to be fine drivers, but not the same as the originals.

It is not possible for me to say what the throw is like since I have no comparison because the surrounds are shot on the originals.

The spider is very different. The "spokes" are much thinner. Does that matter? Probably not. Enough support should be enough, afterall.

Lastly,the magnet is much larger on the originals. Here's a case where size really doesn't matter and since I don't have a gauss meter I can't say if the new ones are inferior or superior in that regard. Maybe they are stiffer and need less magnet.

The voice coils appear to be the same or very close to the same diameter, but that's hard for me to judge.

The 12" replacements are a different story. The paper isn't as rough on the new as the old, but it still feels like paper. The new are slightly lighter (my judgement,not a measurement), but again, that doesn't prove much.

I am REALLY afraid to go with this stiffer material on the 8". If the 12" were a little off I doubt very seriously I could tell the difference at 90Hz or 35Hz. But the 8" are handling all that sound "down there" but not all the way in the basement. And they are firing straight into my face! Not a good place to have an unpleasant "tonal quality."

Bret

[Guest]

>4- Minor air leaks are not a big problem, unless they hiss or chuff or whistle. In terms of bass response, an air leak in a sealed box adds a first order high pass filter which can be estimated as follows:<

I guess that would make holey AR speakers suffer from acoustic reflux.

Bret

[Guest]

Hi, whatever you do, DO NOT trash or discard or disregard your original AR drivers! The best thing for you to do is to have them resurrounded and they will be as good as new. The new replacements that they are pawning off to you these days will most likely drastically alter the original characteristics of your old AR vintage speaker sound. I have been restoring old AR speakers for some years now and can tell you that a good refoam surround job on the original drivers will be the closest you will ever get to an original vintage speaker (AR or otherwise). A/B Tech is not the authority on replacing or restoring your original AR speakers back to original. They do their best to try and source modern made drivers that match the original vintage AR specs, but some of the speaker replacements they sell are FAR from original replacements simply because they are not and cannot be made (cheaply) anymore. Just be careful of some of the advise you get from dealers selling replacement or upgrade parts! They are not always right and of course they are in the business to sell and make money. My best advice (from a picky perfectionist) is to restore your original drivers if all they need is a new surround. I am not saying that there are not superior drivers out there, all I am saying is that those original speakers were designed and voiced with the original drivers. Replacing them with different but similar looking drivers does not mean that they will mate well together. It may come out better sounding and it may come out worse but it will then NEVER be original any longer.

[Guest]

>all I am saying is that those original speakers were designed and voiced with the original drivers. <

I agree. I'm having them repaired. And I'm going to use the new drivers, too. (I suppose I'll be looking for another set of 9s in need of restoration in the meantime.)

I just wish there were some way for me to get these to a lab that could tell us exactly how different the replacement drivers are from the originals. At 140+ lbs in their cartons, I'm not in a hurry to ship them here and there and I'm too far from MA or CA to take a pleasure trip just to find-out.

As you say, with replacement drivers they will never be original. But if we aren't talking "museum piece" I would like to know how the replacement drivers affect the performance of the speaker system as a whole.

Remembering that AR itself changed components from time-to-time I'd say the engineers were tolerant of change, I'm sure not for its own sake.

BTW - I talked with Seth at AB Tech today. Alex was out. I asked Seth about these replacement drivers. He went away for a while and came back explaining that the 8" speakers were a poly-impregnated paper,neither quite poly or paper, but in tests they were virtually identical to the original 8" woofer performance.

I am skeptical.

But then, what possible motivation does Alex have to lie about such a thing? He could probably sell whatever drivers he had to buy.

I asked if AB Tech ever took speakers in for complete restoration. He said that they did. I asked if they pro-actively changed capacitors in the crossovers. His reply was that they did not, but that even if they needed to suitable replacements for the "classic" ARs are not available, period. He didn't elaborate and I had taken-up much of his time. This is frightening since I have more than a casual suspicion that one of my crossovers has a problem.

On a tangent - How hard can this be? Companies have been building speakers for an awfully long time. Surely the technology is mature. Does nobody know how to build new, old-design, AR drivers? A few thousand a year, or one production run of 10,000 units each. . . there are millions of AR speakers still out there. Since I don't know the economics I can't do the math, but it just defies logic. We're talking "stamped" spiders here, not die-cast aluminum. We're talking "paper" not "plastic". We're even talking aluminum wire not silver-whatever.

Judging from this site's popularity (ever-growing) there just might be a ready-made, easily identifiable, market.

What we have here is a case of the amplifiers finally catching-up to the ability of AR speakers to eat them for breakfast. The electronics available today can really make these monsters shine.

Bret

[Guest]

Hi Bret, I know what you are going through! I am sure that the guys at AB Tech mean well and it is great that they are around to serve us. But just be careful (as you said skeptical) of all the recommendations that they might give you. It is not always the best that you can do for your old vintage AR speakers. I have bought several tweeters and parts from A/B tech several years ago and they basically told me the same thing about parts no longer available. But the parts that they say that they did have were not exact original parts. The closest thing I ever got from them was tweeters for AR-3a's. I also remember ordering 4 tweeters for the AR-5 speakers and discussing with them the differences in impedance versus the AR-3a tweeters. They are very knowledgable about those details and acknowleged that there was a difference and that they had a special order in to the driver manufacturer for AR-5 tweeters at that time (years ago). I waited forever (many months!) for them to finally get them in. When I got the four tweeters, I measured them for DCR and they measured exactly the same as my AR-3a tweeters that they sent me. All that they did was print out a little sticker label that said "AR-5..." and stuck it across the back of the tweeters part number as if to fool me into thinking that it was really for an AR-5. Oh well, what can you do. I stuck them into my AR-5's anyway and they seem to play fine. I do have to turn the tweeter level control down slightly to get the original pleasing balance that I personally like. But that was good enough for me so I never did call them back to complain about it. Also, I ordered tweeters for my AR-4x's from AB Tech (again a few years ago) since AR-4x tweeters are were hard to find and no longer in production. They sent me some el'cheapo Pioneer tweeters that fit the mounting hole but were nowhere near as good or same sounding as the original AR-4x tweeters. Before getting these tweeters from AB Tech, I had ordered a few of these very same Pioneer tweeters from Parts Express for only a few bucks a piece! AB Tech charged me an arm and a leg for them (way more than they are worth) and when I got them and saw that they were the same, I was very disappointed. I remember calling them back and discussing this with them and they did not fess up until I told them I know that they are Pioneer tweeters because I have a box of them from Parts Express right in front of me!

Then they admitted it was just a close replacement AR-4x part that they sell because the original AR-4x tweeters cannot be sourced anymore. So I have a bunch of these tweeters buried in my garage doing nothing.

This is not to disparage AB Tech BTW, it is just to show you that you cannot always relie on these parts or service centers to give you the straight scoop or to restore things back to real original. I believe AB Tech serves as a good source for AR speaker parts when you are in a jam and cannot find it elsewhere or are in a rush and cannot wait to locate a part. But when you order a part and want it to be original and not something that they recommend as a close match, ask them to make sure, so that you won't get surprised when you receive them. I don't blame AB Tech for trying to sercve this niche' market segment, but they should also tell customers up front that what they will be getting is not the real original spec driver(s) but a what they have deteremined is a closest match.

As for crossover capacitors, you can easily find replacement parts from many electronic parts sources today. You need not go through AB Tech for those parts. Also they need not be exactly the same make or brand or style capacitors. What matters most is the capacitors value and voltage rating. If your big AR-3a 150ufd capacitor has failed (and I have one that has) then you can simply remove it from the circuit and replace it with a 150ufd electrolytic non-polarized cap rated at 50VDC or above. Of course that big rectangular block cap used in the AR-3a is dual capacitor with two sections (or two caps in one) So you will probably have to replace the other cap section (which is in the midrange circuit) too with the proper value.

Anyway, crossover parts are not a problem to restore the speakers back to original or close to original sound. That can be done for the crossover repairs today. But speaker drivers, that is a whole different matter and it DOES matter if you want to retain as close as possible what the original sound of the speakers were (are).

Anyway, this is getting too long, so I'll cut it off here for now. :-)

[Guest]

>As for crossover capacitors, you can easily find replacement parts from many electronic parts sources today. <

Oh yeah, I know I can get the same values. Ken or Tom or one of those "smarter than I am" guys was saying that some of the attributes of a capacitor aren't measured in "uF" and that it would take more test equipment than I'll ever own to "match" the new to the old.

Bret

"I have had a perfectly wonderful evening, but this wasn't it."

Groucho Marx