Video of early '60's AR3 woofer with proper acoustic suspension seal

[redpackman]

How it should look if the acoustic suspension seal is right:

 

 

[ReliaBill Engineer]

Not so sure. If it’s truly sealed, pushing in on the woofer cone compresses the air inside the cabinet. Air is a spring. The compressed, springy air should push back on the woofer cone with the same force you used to compress it.

If there is an air leak, (small one) pushing on the cone will push air out of the cabinet. Releasing the cone will cause a vacuum that will slow down the return of the woofer cone, as air is sucked back into the cabinet.

 

[RTally]

The cabinets for acoustic suspension speakers do not have a tight seal. If they did, the woofers would pump based on barometric pressure. There should be some leakage, although only a small amount.

The technique I use is to depress the woofer cone and HOLD the depressed position for at least 5 seconds (preferably 10 seconds) before releasing. Holding the cone in allows the internal cabinet pressure to equalize with atmospheric pressure. If the cone is not depressed long enough, the compressed air does not have a chance to fully escape and will help push out the cone, giving a misleading result with a slightly faster return time.

After releasing the cone, measure the time for the cone to return to its resting position. When I test KLH speakers, a return time of less than 1/2 second indicates that there is a leak somewhere. The quicker the return, the more likely the leak is too large. A return time around 1 second or more is optimum and indicates a good cabinet seal. I will let the AR experts advise on the optimum return times for AR speakers if the return time is different.

[ReliaBill Engineer]

Mine takes about 1-2 seconds to return. If I hold it in for 5 seconds, it still takes the same amount of time to return. Here, I may not have pushed it “in” far enough. But I can see and hear ample evidence of a good seal.

 

 

[crumpets]

Thanks for the visuals. Very helpful.

Does sealing the cloth surround on those woofers have an effect on the performance, or is it more to keep them from cracking/further deteriorating?

[JKent]

Better bass. 

[crumpets]

Ok, good one. Has anyone had success with any alternatives to the cloth surround sealing product offered by vintage_ar on the bay, or is this still considered the best option? Being an ar enthusiast in the southern hemisphere sure has its disadvantages, and postage is one!

[JKent]

It’s the only thing to use. 

[ReliaBill Engineer]

On 6/12/2023 at 7:41 PM, crumpets said:

Ok, good one. Has anyone had success with any alternatives to the cloth surround sealing product offered by vintage_ar on the bay, or is this still considered the best option? Being an ar enthusiast in the southern hemisphere sure has its disadvantages, and postage is one!

I don’t know what vintage_AR uses. I used an extremely thin membrane of clear butyl rubber applied to the backside of the surround, so it isn’t visible. 

[crumpets]

Thanks ReliaBill, not sure if I'd trust myself getting a suitable product. Will probably go for the tried and tested.

[ReliaBill Engineer]

From pics I’ve seen, the vintage_AR dope is thick and messy. It only needs to be thick enough to fill in the very small pinholes in the fabric surround. It needs to be thin enough not to alter the ability to flex; you don’t want to alter the woofer performance. Personally, I don’t like the wet-looking dope showing on the outside of the surround. It never seems to look professional.

 

Before applying clear butyl membrane:

 

After applying clear butyl membrane to the back side of the surround:

 

 

 

 

 

[Jim Pearce]

Okay so where does one source this clear butyl membrane, pray tell?

I've had some good success thinning the liquid stuff with tolulene.

[JKent]

30 minutes ago, Jim Pearce said:

Okay so where does one source this clear butyl membrane, pray tell?

I've had some good success thinning the liquid stuff with tolulene.

Don't ruin your woofers. Roy's sealant available from Vintage-AR is the only thing that is true to the original and will never harden.

[RoyC]

On 6/14/2023 at 11:08 AM, ReliaBill Engineer said:

From pics I’ve seen, the vintage_AR dope is thick and messy. It only needs to be thick enough to fill in the very small pinholes in the fabric surround. It needs to be thin enough not to alter the ability to flex; you don’t want to alter the woofer performance. Personally, I don’t like the wet-looking dope showing on the outside of the surround. It never seems to look professional.

After applying clear butyl membrane to the back side of the surround:

The sealant is not at all "thick" nor is it "messy" if properly applied. In fact, it is deliberately very thin to act as a supplement to the original (which did not magically go away). It remains tacky so it will not form an additional membrane, which has the potential to affect performance by altering mass and compliance. The high percentage of toluene in it can also serve to loosen any hardened original sealant. As for not liking the way it "looks"...well these are, after all, AR speakers. Eye of the beholder, etc.:).

Much time and measurement (primarily Fc and Fs) went into developing the formula, along with some information from Roy Allison (through Tom Tyson). It should also be noted that much experimentation was conducted with various membrane-forming materials beforehand.

Roy

[newandold]

On 5/23/2023 at 1:17 AM, redpackman said:

How it should look if the acoustic suspension seal is right:

 

 

….. as is the case with all sealed enclosure acoustic suspension systems. When you have a DUAL woofer system on a particular speaker and press as you have done and all is good, you will see the opposing woofer instantly move as if they are one. your test was fine except I would be leery about pushing a woofer that old that far down. 

[ReliaBill Engineer]

On 6/30/2023 at 5:57 PM, RoyC said:

The sealant is not at all "thick" nor is it "messy" if properly applied. In fact, it is deliberately very thin to act as a supplement to the original (which did not magically go away). It remains tacky so it will not form an additional membrane, which has the potential to affect performance by altering mass and compliance. The high percentage of toluene in it can also serve to loosen any hardened original sealant. As for not liking the way it "looks"...well these are, after all, AR speakers. Eye of the beholder, etc.:).

Much time and measurement (primarily Fc and Fs) went into developing the formula, along with some information from Roy Allison (through Tom Tyson). It should also be noted that much experimentation was conducted with various membrane-forming materials beforehand.

Roy

“From pics I’ve seen, the vintage_AR dope is thick and messy. It only needs to be thick enough to fill in the very small pinholes in the fabric surround. It needs to be thin enough not to alter the ability to flex; you don’t want to alter the woofer performance. Personally, I don’t like the wet-looking dope showing on the outside of the surround. It never seems to look professional.”

As you see, we both said the same thing here. I’ve seen many pics of this toluene-based dope applied, on FB groups and in SH, VE, and AK forums. Just looks unsightly to me. Certainly quite a ways from original.
 

Don’t get me wrong, I tried many formulas myself, practicing on fine cloth, parchment paper, on bare steel, to get the formula to produce an extremely thin “wash” on the fabric, and also a primer/cleaner on the cloth surround prior to application. The butyl-based formula I wound up using is 95% by weight thinner/solvent. It only leaves an extremely thin sealant layer that is resistant to decades of ozone, heat, flexing. And, it doesn’t attract dust, poly fill, fiberglass or rock wool fibers, since it’s not tacky or sticky. It’s so thin that you can’t tell it has been applied at all, by looking at the front (outside)  of the surround. I’m very happy with the results.  I used about 50/50 Stoddard Solvent and Naphtha. Stoddard is more aggressive than Naphtha, but Naphtha is slower to evaporate. It makes the butyl easy to apply as a “wash” with a brush in a very fine layer, then levels nicely. 

[RoyC]

9 minutes ago, ReliaBill Engineer said:

Don’t get me wrong, I tried many formulas myself, practicing on fine cloth, parchment paper, on bare steel, to get the formula to produce an extremely thin “wash” on the fabric, and also a primer/cleaner on the cloth surround prior to application.

Do some measurements and let us know the results.

The tacky butyl materiel was also used on a number of tweeters (not AR) over the ages.