Hi Harry.
I believe I can shed some light. I agree that all surrounds are not the same. If they were, we would save an awful lot of money by stocking only a few different sizes rather that 220 different models.
Let me start by clarifying something. The larger retailers I mentioned, (Those who have websites and facilities outside of a simple eBay store) all have ACCESS to the exact same foams. That is not to say that, in all cases, they offer the exact same foams for a particular application. Though they probably should. On the vast majority of models, our offerings are all the same aside from the adhesive in the kit. ( I will come back to adhesives in a moment) Though there are several replacement foams that are made for a specific application rather than using what people call a "Generic" or "standard" or "Universal" foam, the vast majority of speakers actually used those same "Generic" foams when they were first manufactured. Most speaker companies don't make foam, they make or assemble speakers. Foam companies generally make foam for these speaker companies. A model-specific die is very expensive to have made, and hard for many speaker companies to justify, so they actually used foams that were readily available when they built their woofers. JBL, Boston, Cerwin Vega, Advent, Polk, and Infinity were among the companies that had at least a few of their own dies made from their designs, thus making the foams proprietary to their models. Some companies, such as Boston, allowed other companies to use their surrounds on some of their models (EPI, Genesis, EV, Fried, Paradigm).
With regard to the use of filleted foams, I too have heard this commentary in the past, but can't say that I necessarily agree. I have also heard about using the JBL 125A surrounds on the AR90. The Boston foams, as well as the 125A foam are thinner and more pliable, and also have rolls that are about 1/16" wider than the standard 10" angle-attach surround. The 125A is actually one of the foams that a few retailer do not bother to stock (But we do). It is so close in measurements to the 10" angle foam, that they simply substitute for it with that less-expensive foam. Many sellers subtitute a standard 8 in place of a true filleted Boston foam as well. It is cheaper for them, and makes their kits more profitable for them. I digress, as I often do... I feel that many people who recommend the Boston foams for their AR models are comparing the foam that they are replacing to the stiffness of the replacement. I feel that they have forgotten (Reasonably) what the foams actually felt like when they were first installed 30 years ago. With age, like nearly anything else, they become much softer, and more pliable. In many cases they also become thicker as a result of the foam decompressing. Over time, foams tend to break in, and soften. The speakers lose their original punchiness (sp?), and end up with more bass response, though it is not quality bass. The thinner foams such as the Bostons, and 125As were originally used as required to contribute to the very high-sensitivity of the models they were originally used on. (I believe the AR90s were around 87db. Sensitive, but not as high as these others)
To answer your question...I do not agree with using the Boston or JBL foams on the AR models. The AR models nearly all used what was a standard foam at the time, and therefore that is what we use to replace them. On the flipside, we DO have all of the filleted Boston foams if you want to go that direction, as well as the actual JBL 125A foam, adn we can substitute them into the kits at your request.
On the topic of "Sealing" brought up in an earlier response to my post; I believe that this is a product of the adhesive more so than the foam. Adhesives are the biggest difference between most of our kits. Many people like to use Elmer's, or Aleen's Tacky Glue for their repairs. While the convenience of a longer working time is nice for some people, the end result is an improper seal. These adhesives are water-based PVAs. They bond cleanly and permanently to a paper cone, as well as to dust caps made of that and other porous materials. However, they do not bond or seal properly to steel, aluminum, poly, injection-molded graphite, or other non porous surfaces. If you are in a particularly humid climate, forget about the bond sealing and lasting for any significant amount of time. Many sellers' kits include a similar white or even black PVA adhesive that, while NOT Elmer's as often accused (It is considerably more acidic), is still water-based and subject to the same weaknesses as the Elmer's. We sell the white as well, but only for dampening cloth surrounds, repairing paper cones, and joining non-flexing porous surfaces together.
The non-eBay-only retailers and repair facilities, such as ourselves, and others previously mentioned, use solvent-based adhesives just like the factories used originally. They bond properly to the materials involved, and don't break down in certain atmospheric conditions. Our primary adhesive has a base that has morphed over the years. Our newest formula, which comes in all of our kits, no longer even contains acetone (A common solvent ingredient), but rather 2 parts Toluene and 1 part Hexane, as these materials lend themselves to better bond with aluminum and poly in particular. The white water-based adhesive costs, wholesale, about 1/4 of what the quality solvent-based adhesives do. This may be a reason that so many seller use it in their kits instead of the proper adhesives. It increases their profitability. Would you rather get something a little cheaper, or do the job with the correct materials? I choose the latter. I hope this rambling mess made some form of sense.
Thanks,
Paul
