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Salvaging AR3 and older cloth surround woofers


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A recent customer sent me a pair of Alnico AR3 woofers with cloth surrounds in very bad shape. He insisted I replace the cloth with foam.

The cone OD and frame shim size are about the same as new, foamed AR 11 inch woofers and the foam I had in inventory seemed a good fit at first try.

Removal of the cloth is the trickiest part. After that, the job is like most regular refoam jobs.

I painted a generous coating of Goof Off on the outer rim of the cloth surround where it's glued to the basket's fiberboard shim. After an hour or two, I began to separate the surround from the shim by pushing up with my fingers from the underside of the cloth. This delaminated a thin layer of the shim in a number of areas by not enough to seriously alter its thickness. After the entire periphery of the cloth surround was separated from the shim, I cut the cloth in one spot in a line pointed towards the dust cap and stopped just short of the cone edge. At that point one can begin to tear the cloth the rest of the way then begin to pull it in a direction tangent to the cone's OD. The cloth with nicely separate from the cone's edge all around with continuous tension applied until the cloth is separated from the cone. What remains is to clean the residue from the cones edge and prepare it and the frame shim for gluing of the new surround.

The underside of the cloth surround was measured and compared to my stock foam. The cloth roll's uderside measured 7/8 inch, whereas my foam measured 3/4 inch. The difference, as it turns out didn't make any difference. After the foam was installed and dried, I ran a WT3 test. The Fs with the foam after 8 hrs of break in at 20 hz & 2 volts power level was only 1 hz higher than the woofer with the cloth surround I tested before starting the replacement. Perhaps the foam will break in a bit more with normal use and so, a vintage pair of AR3 woofers can live again and bring their owner musical enjoyment.

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I understand that you repair to suit a customer's needs, but sometimes the customer may not understand that the old cloth surround will last much longer than the new foam surround. As a business person, you need to respect your customers wishes.

In my experience, the few wrinkles in the cloth surrounds on AR-4x and AR-3, 3a drivers are not an issue; they are cosmetic. The real issue I have faced is aging of their spiders, but not in all units, just in a few.

An example of this was a pair I restored for a good friend (one of two pair that were not for my family!) This pair of woofers came from AR-3 manufactured in 1966. When restored in March 2007 as AR-3a Limited units, they had a very low Fc, ~37 Hz, and could be played at high power levels with no problems. In June 2009 the voice coil of one unit began to hit its back plate; my friend enjoys listening at high levels. To verify the cause, I placed small copper weights on each cone and plotted cone displacement versus load and found one driver quickly and linearly reached the back plate, whereas the other had a much lower (and linear) slope, but did not hit the backplate when it reached its maximum excursion. The solution was to have Bill LeGall of Millersound replace both spiders. When finished, Fc was about 40-41 Hz.

One of the cues to a weak spider is low Fc and Fs which these units exhibited, even though they did not bottom out when first assembled. I suspect that two years of high listening levels hastened the end of life of an elderly spider.

Given the choice, I would prefer to replace the spiders and keep the cloth surrounds--coated with a bit of Roy's excellent tacky butyl rubber compound. These should now be good for many more years of listening enjoyment with no worry of crumbling foam!



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Another problem I've found on many AR3 and 3a woofers I see is partially loosened glue joints on the fiberboard shims where they are glued to the frame. Both the surrounds and the spider's. Air leaks will result in an unglued surround shim. A more severe case will also cause a rattling noise at the right frequency.

Replacing original spiders can be difficult on the AR3 and older woofers because it's uniquely glued to the cone about a 1/4 inch or so above where the voice coil attaches to the base of the cone. Most spiders are glued to the voice coil and the cone. Additionally, those old spiders are made from a very fine weave cloth and there's little or no resin binder to aid in firming up their flexibility.

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