AR 2ax, woofer testing and more

[Guest spgjmf]

hi folks,

Back in June I managed to restore to working my Dad's ar-2ax speakers and have enjoyed them this summer. I have seen a few post here about the surrounds on AR woofers. The speaker I have have cloth surrounds,

so no rot, but are they air tight??

what is the woofer "push" test? Is there a way to tell if something needs to be done to the cloth? if so what?

Also , it seems one mid range driver might be bad, its very distorted. could be I need to work on the pot more or replace.

I guess I'll check eaby for replacements if needed.

best,

Jeff

[Carlspeak]

>hi folks,

>

>Back in June I managed to restore to working my Dad's ar-2ax

>speakers and have enjoyed them this summer. I have seen a few

>post here about the surrounds on AR woofers. The speaker I

>have have cloth surrounds,

>so no rot, but are they air tight??

>

>what is the woofer "push" test? Is there a way to

>tell if something needs to be done to the cloth? if so what?

What I did with mine is put my lips to the surround and try to suck air thru it. My cloth surrounds seemed pretty tight - even though they indeed passed light thru them, which was a concern of another poster.

>

>Also , it seems one mid range driver might be bad, its very

>distorted. could be I need to work on the pot more or

>replace.

>I guess I'll check eaby for replacements if needed.

I have 2 AR2a midranges for sale. $20ea. plus shipping.

>

>best,

>Jeff

Remember, it's all about the music

Carl

Carl's Custom Loudspeakers

[onplane]

>What I did with mine is put my lips to the surround and try to

>suck air thru it. My cloth surrounds seemed pretty tight -

>even though they indeed passed light thru them, which was a

>concern of another poster.

Carl, your test is probably plenty good enough. Many materials are translucent, but remain air tight. Just look at those ubiquitous sandwich baggies.

Now, if there are areas of concern in cloth surrounds, I'll bet there is a simple solution. Most fabrics have a sizing agent added to protect the fibers. This sizing agent can consist of any number of things, but generally you want something flexible or "gummy".

Carl, you might try a very, very light coating of shellac in the problem areas. A light coating should stick and seal, yet NOT change the stiffness of the fabric. It will remain translucent, however.

Regards,

Jerry

[Carlspeak]

>>What I did with mine is put my lips to the surround and

>try to

>>suck air thru it. My cloth surrounds seemed pretty tight

>-

>>even though they indeed passed light thru them, which was

>a

>>concern of another poster.

>

>

>Carl, your test is probably plenty good enough. Many

>materials are translucent, but remain air tight. Just look at

>those ubiquitous sandwich baggies.

>

>Now, if there are areas of concern in cloth surrounds, I'll

>bet there is a simple solution. Most fabrics have a sizing

>agent added to protect the fibers. This sizing agent can

>consist of any number of things, but generally you want

>something flexible or "gummy".

>

>Carl, you might try a very, very light coating of shellac in

>the problem areas. A light coating should stick and seal, yet

>NOT change the stiffness of the fabric. It will remain

>translucent, however.

>

>

>Regards,

>Jerry

>

>

I'm not concerned at all about my AR2a woofer cloth surrounds. I was trying to help Jeff with his concerns.

Remember, it's all about the music

Carl

Carl's Custom Loudspeakers

[dynaco_dan]

>>>What I did with mine is put my lips to the surround

>and

>>try to

>>>suck air thru it. My cloth surrounds seemed pretty

>tight

>>-

>>>even though they indeed passed light thru them, which

>was

>>a

>>>concern of another poster.

>>

>>

>>Carl, your test is probably plenty good enough. Many

>>materials are translucent, but remain air tight. Just

>look at

>>those ubiquitous sandwich baggies.

>>

>>Now, if there are areas of concern in cloth surrounds,

>I'll

>>bet there is a simple solution. Most fabrics have a

>sizing

>>agent added to protect the fibers. This sizing agent can

>>consist of any number of things, but generally you want

>>something flexible or "gummy".

Hi there;

Shellac is fine for wood, not speaker surrounds.

Using shellac, thinned or not, is asking for cracking of the surround material, in a very short period of time.

TomT has mentioned in other posts, something called, Armorall (spel) as a suitable compound for the cloth surrounds.

Soft and subtle is a requirement for these cloth surrounds.

You cannot add, just any compound and expect no changes to the surround mass or a reduction of flexibility.

I will guess that a siliconized compound would be desirable.

To go to the root of the problem, the cloth surround.

I would not touch a surround, unless there is dry rot and holes or cracks larger than a pin hole.

The cloth is a rubber type coated gauze, I believe.

Carl has a lot of actual field experience and I would value his very competant advice.

>>Carl, you might try a very, very light coating of shellac

>in

>>the problem areas. A light coating should stick and seal,

>yet

>>NOT change the stiffness of the fabric. It will remain

>>translucent, however.

>>

>>

>>Regards,

>>Jerry

>>

>>

>

>I'm not concerned at all about my AR2a woofer cloth surrounds.

>I was trying to help Jeff with his concerns.

>

>Remember, it's all about the music

>

>Carl

>Carl's Custom Loudspeakers

[johnieo]

>your test is probably plenty good enough.

The traditional test is to depress, with care, the cone by placing three fingers on the cone just outside the dust cover. Push the cone in slowly until it bottoms, then release suddenly. If it returns in two-to-three seconds or more, then it is fine; if it returns to equilibrium suddenly, there is an airleak somewhere, but not necessarily in the surround.

>you might try a very, very light coating of shellac in

>the problem areas. A light coating should stick and seal, yet

>NOT change the stiffness of the fabric.

Dry shellac is brittle like glass (the shell of the lac bug!). take a thin piece of plastic baggie, coat it with shellac and let it dry. Next day flex the bag... There are a couple of coatings that seem to work. One is Loctite (brand) butyl rubber sealer. However, this must be thinned greatly with something like lacquer thinner or hexane until it is near water consistency. Then only brush on areas that seem very thin or translucent and do so with great care.

A number of earlier discussions about cloth-surround drivers can be summarized with a comment like: "if it ain't broke, don't fix it." I have two AR-4x woofers that are completely useless because they have been destroyed with beautiful looking, thick coatings of this (or similar) compound. Those units have Fs values of ~60 Hz (should be 31-32 Hz), thus destroying their lowest register.

[Carlspeak]

>>your test is probably plenty good enough.

>

>The traditional test is to depress, with care, the cone by

>placing three fingers on the cone just outside the dust cover.

>Push the cone in slowly until it bottoms, then release

>suddenly. If it returns in two-to-three seconds or more, then

>it is fine; if it returns to equilibrium suddenly, there is an

>airleak somewhere, but not necessarily in the surround.

>

>>you might try a very, very light coating of shellac in

>>the problem areas. A light coating should stick and seal,

>yet

>>NOT change the stiffness of the fabric.

>

>Dry shellac is brittle like glass (the shell of the lac bug!).

> take a thin piece of plastic baggie, coat it with shellac and

>let it dry. Next day flex the bag... There are a couple of

>coatings that seem to work. One is Loctite (brand) butyl

>rubber sealer. However, this must be thinned greatly with

>something like lacquer thinner or hexane until it is near

>water consistency. Then only brush on areas that seem very

>thin or translucent and do so with great care.

>

>A number of earlier discussions about cloth-surround drivers

>can be summarized with a comment like: "if it ain't

>broke, don't fix it." I have two AR-4x woofers that are

>completely useless because they have been destroyed with

>beautiful looking, thick coatings of this (or similar)

>compound. Those units have Fs values of ~60 Hz (should be

>31-32 Hz), thus destroying their lowest register.

I agree 100%. I have refoamed numerous AR woofers that have been coated heavily with black rubber goop. There's no way this can be done without significantly altering the woofer's performance. I can only surmise this has been done by people who just want to salvage them but are not aware they are doing them more harm than good. Hopefully, they are not doing this to save a few bucks - knowing they may be messing them up.

Remember, it's all about the music

Carl

Carl's Custom Loudspeakers

[onplane]

Hi, Vern!!

Rubber??

I've never seen a cloth surround and just assumed they were treated cloth. Further, I wasn't suggesting any "coating" what I was suggesting is a highly "thined out" suspension that would be absorbed by the cloth.

This make no sense whatsoever if the cloth is rubber coated as the rubber will prevent any absorption.

Now, pure silicone will be absorbed by rubber. Probably not enough to do any good though.

The shellac idea will clearly not work as I described.

Sorry for the bad suggestion.

Regards,

Jerry

[dynaco_dan]

>Hi, Vern!!

>

>Rubber??

>

>I've never seen a cloth surround and just assumed they were

>treated cloth. Further, I wasn't suggesting any

>"coating" what I was suggesting is a highly

>"thined out" suspension that would be absorbed by

>the cloth.

>

>This make no sense whatsoever if the cloth is rubber coated as

>the rubber will prevent any absorption.

>

>Now, pure silicone will be absorbed by rubber. Probably not

>enough to do any good though.

>

>The shellac idea will clearly not work as I described.

>

>Sorry for the bad suggestion.

>

>Regards,

>Jerry

Hi Jerry;

When I wrote a rubberized compound, this was all the memory that I have.

I was not implying rubber, as in Dynaco neoprene surrounds, but perhaps a thinned rubber based paint or similar.

TomT will know for certain.

As I mentioned earlier, I am certain, that TomT has mentioned Armorall (spel) as a suitable coating, 2 coats over a 2 day time period.

When I read on ebay what some sellers have done to an AR speaker and claiming they have upgraded them, I cringe.

Vacuuming out all the old fiberglass insulation and replacing it with a poly fill.

A pound is not a pound, in this case.

There is a vast amount of polyfills available, some audio specific, that may be suitable on the marketplace, including that used in the better sleeping bags.

If there is anyone here who has the capabilites to do that particular upgrade, it would be Ken Kantor, or equal, with the proper test equipment.

I am sorry, if I missed out on identifying anyone else on this site, with that same capability.

At least shellac is out of the way.

Alleens (spel) white glue has been mentioned before, and I still would not suggest that.

Armorall (spel) seems to be the compound of choice, barring someone else finding another material.

[Guest Rod H.]

I considered using Aleen's tacky glue thinned, but then found something I think is better.....a bottle of Aleen's flexible/ stretchable fabric glue in my wife's craft stuff. It's already thinner than the tacky glue, but I thinned it a slight bit more. It's possible to brush it on in an extremely thin layer which absorbs into the fabric and bridges the holes in the weave, and frankly I was very impressed with how it worked. The cloth on the AR-2axs that I used it on looked like there was no longer treatment remaining on them, and they passed air like crazy.

Personally, I have lots of confidence that this stuff is good for this application, but to be prudent (after all, we're talking about antique drivers) I'd encourage you guys to get a bottle and try it on some similar scrap fabric as an experiment before using it on a driver.

[Guest Rod H.]

Jeff, Unless I missed it nobody answered your question about the "woofer push test". To do this you carefully and evenly push the woofer in. The amount depends on how much it will move easily, and is pretty intuitive. Basically an amount the woofer would normally move playing deep bass at a moderate level. Release the woofer and watch. If it springs back immediately you don't have a very well sealed woofer/cabinet. If it takes a couple seconds you have an OK seal. Some exceptionally well sealed cabinets/woofers will take several seconds to return 90% of the way, then will slowly return the rest of the way over several more seconds. Opinion will vary on how well cabinets need to be sealed, but if the woofer immediately springs back I think that isn't really very good for acoustic suspension.

Rod

[soundminded]

I'd think it was the other way around. If the woofer pushes back immediately, it means air pressure inside the cabinet is trying to equalize the pressure outside by moving the woofer cone out to increase the volume of the inside space. If there is a leak in the suspension or cabinet, it is oozing through the leaks and not pushing nearly as hard on the cone. The relatively weak mechanical suspension should take longer to restore the cone to its original nominal spot. At least that's what I'd expect. Can you explain why this is wrong?

[RoyC]

The "woofer push test" is a standard test for any acoustic suspension speaker design. The cabinet is supposed to be tight enough to allow atmospheric pressure to slowly equalize after displacing cabinet air by pushing on the woofer, thus allowing the woofer to slowly return to its original position.

An excerpt from Mr Villchur's patent document...."The amount of leakage is sufficient only to equalize long-time variations due to atmospheric conditions but is insufficient to affect the inherent elastic stiffness of the enclosed air cavity for voice coil excursions occurring when reproducing sound. In other words, the enclosure is designed to provide an acoustic seal, that is, one which does not allow significant air leakage over a period corresponding to a half-cycle of the lowest frequency encountered."

This document should be basic reading for those who fancy themselves smart enough to re-engineer the original designs.

Roy

[Guest Rod H.]

If the speaker and cabinet were sealed perfectly what you describe would happen. It would feel like pushing on a balloon. I'll confess I've never seen a speaker sealed that well. When applying gentle pressure the cone always moves, although it may take several seconds. The scenario I see is that when the cone is pushed some air always finds a way to leaks out of the cabinet. When the cone is released, if the cabinet is well sealed (but still has a bit of leak) the cone will return slowly as the air pressure equalizes. On really leaky cabinets the cone returns immediately just as if there were a big hole in the cabinet.

On the AR-2Axs I was just fiddling with the woofers would just move in like there was a hole in the cabinet when I applied pressure to them. When released they would return, acting almost like they were in free air and being returned to neutral position by only the suspension. After sealing the surrounds they would still push back into the cabinet, but I could feel a resistance as the air was pushed out somewhere, then they returned slowly.

This procedure was well described in an article in Speaker Builder magazine maybe 20 years ago. The author thought that a time of a couple seconds for the return was sufficient. If the cone returned most of the way, then very slowly over several more seconds finally reached neutral, you had a very good seal indeed.

The same article also went into how to use talcum powder to find leaks in cabinets seams and so forth, and was quite interesting.

If I was ever to push on a cone and it felt like there was no give and I was pushing on a balloon, I'd immediately stop and pronounce it amazingly well sealed!

Rod

[RoyC]

As we can see from Mr Villchur's patent, a totally airtight cabinet would not be appropriate.

There have been high-end driver manufacturers (Dynaudio, Scanspeak) that have produced woofers which were to be optimized for "aperiodic loading", quasi-acoustic suspension designs based upon less resistive air pressure within the cabinet...through controlled leakage.

Roy

[Guest Rod H.]

I haven't read the patent, but intuitively it seems like a perfect seal would be undesireable. For one thing, normal variations in atmospheric pressure due to elevation and weather would be a serious problem!

Rod