* “Refoaming” refers to the replacement of a damaged, cracked, or “rotted out” (dry rot) foam outer suspension (also known as a roll, or “edge”), on a woofer or midrange speaker, with a new foam suspension.  

If you are having a speaker “refoamed” or “re-surrounded”, be sure the shop does not cut corners.  They should use correct shims to center the coil while the new roll is installed and the adhesives are drying.  Centering must be precise laterally (ie., concentric to the pole piece and top plate, and no “tilt” of the coil, relative to the pole piece), but also the vertical position of the coil in the gap is important, for best performance.  

We discussed the “tilt” issue in an e-mail to Phillip Holmes of Dagogo.com, a little while back:

” …what causes miscentering of voice coils in “refoam” jobs. It’s usually not the forces in the spider itself that causes the miscenterings: It’s the inability of the spider by itself (or assisted only by weak forces generated by the current some people like to run through the driver for “centering”) to keep the coil from “tilting” a bit, that causes the problems. For example, let’s say the cone was not perfectly level, originally (extremely common), and one glues in a new surround, which (if the new roll is unwarped, concentric, etc.,) would tend to level the cone. That might sound desirable, but, in “levelling” the cone, the coil, presumably aligned nicely when the manufacturer glued everything together, would now be tilted slightly. Conversely, a “level” cone can easily be pushed out of level in the re-surrounding process, overwhelming the weak ability of the spider + “current” to resist the tilt. If the cone alignment changes, the coil’s alignment will change with it. It can take only a couple thousandths of an inch of coil tilt to reduce the amount of “clean” excursion available, significantly, when the driver is being “pushed” briskly. This of course does not cover the problems that may occur if the voice coil height in the gap is not “held” correctly, when the new roll is installed.”

The full discussion including Phillip’s bad experience with a poorly done refoam job, is reproduced in his review of our room at the 2009 Lone Star Audio Fest.   (Scroll down a few paragraphs, but don’t miss his other reviews, also!)

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Also, from our Driver Reconing FAQ page:

Q:  The foam surround on my woofer has rotted out.  Can my woofer be repaired by simply replacing the foam surround, instead of replacing the driver or doing a complete recone job on it?

A:  Generally, yes, but there are some pitfalls to watch out for:

• 1)  In rare cases, a driver has an odd-size roll that was custom tooled for it, and either the roll is proprietary (the part supplier cannot legally or ethically sell the rolls to anyone but the company who paid for the tooling) or for some other reason, the parts are not available.  (The tooling may have been scrapped, “lost to time”, or the cone manufacturer or recone parts suppliers simply do not see enough “demand” to make it worthwhile to set up to do a production run.  In a couple cases we have hunted down a part, finding it at the “original” brand name speaker maker or their “descendant”, etc., only to find that the part was so ridiculously overpriced that some other option made much more sense!)

• 2) There is other (visible) damage to the driver that a consumer may not know to look for.  Examples include:

a) Slight creases or bends in the cone, indicative of a future failure of the cone.  This is especially  true of paper cones, but some plastic and other cones can turn out to be on the edge of “cracking up” upon closer inspection.  In the case of paper cones, be particularly sure to look at the cone, right at the the edge of the dust cap, for any creasing, cracking, or buckling.  (If you think a slight weakness in a cone body is not important or won’t get enough stress to cause a failure, later, check out these links for some cool graphics:  http://www.loudsoft.com/loudsoft/my%20files/LOUDSOFT_FEM_Examples2.pdf 

http://www.loudsoft.com/default.asp?site=Articles

Really wild radial ripples can occur too — if anyone can contribute an image of such, please let us know!

b) Frayed tinsel leads.  Even slight fraying almost always means replacement is necessary.  Resoldering them “a little shorter”, etc., is usually a recipe for re-failure in the near future.

c) The spider (inner suspension) is deformed past recovery.  This includes any variation in the “levelness” of the spider as one looks around it (ie., travelling in a circle).  It also includes upward or especially downward “dishing” of the spider that causes an “oilcan” type of behavior when the cone is moved forward and backward aound the normal “rest” position.

• 3) There is non-visible damage to the driver.  These are the really tricky ones… :

a) The coil winding have scraped the top plate, resulting in a partial short or a spot where arcing can occur.  (Pic of a “scraped” JBL coil coming soon.)  PR Audio has specialized methods of testing for this type of problem and finding most (not all) cases of it.

b) The bottom of the coil has hit the back plate, damaging the coil.  This can cause a “voice coil rub”, a coil that has simply lost clearance to the magnet structure, a dead coil, or problems similar to those of a “scraped” coil.

c) The coil has scraped the pole piece.  Usually this results in weakening of or damage to the bobbin, which can be anywhere from nearly impossible to detect, without at least partial disassembly of the driver, to a fairly obvious failure.

d) Other bobbin damage.  This is usually caused by bottoming, or just the coil “rattling around in the gap”, but without serious scraping damage.  Very often with Aluminum bobbins in particular, the section of the bobbin above the coil windings, but below the spider, is deformed, or may not appear deformed but has work hardened and may eventually crack.  (We will have a great picture of an insidious example of this beginning, coming soon.)  The problem here is that the beginning of such a problem can be almost impossible for anyone other than an experienced professional to detect, and it sometimes can require partial to complete disassembly of the driver to confirm.  (Is that a scratch, or is it the beginning of the formation of a crack?)

e) Bobbin tape damage.  This is a bit of a wild one:  Some of the tapes used in the past as an interface between the voice coil bobbin (usually Aluminum or Kapton / Kapton-type material) and the glue joint to the spider and cone body will themselves “delaminate” under stress.  The stress of operation while the roll is failing / has failed can make matters worse.  (Imagine that cone at the links above, without the roll there to help control it, and then consider that all that flexing WANTS to go down into the voice coil, but the glue joint at the coil, and the coil itself, are trying to hold everything together.)  So… it may not seem like there is a problem, one refoams the driver, and then discovers there is still a buzz or other problem, basically because the cone and / or spider are not quite completely attached to the voice coil any more.  Again, there ARE ways a very experienced and attentive “pro” can catch this in most cases, but even Paul has been “tricked” a couple times, by this one.  (A failure just beginning in a spot that cannot be easily observed is “Murphy” at his sneakiest!)

As he writes this, Paul is probably forgetting a couple of the really rare examples of problems that can turn up (and he may be reminded by an actual unit coming in for repair soon!)

All these possible problems probably add up to maybe 10-20% of the drivers we see coming in for “roll replacements”.  So, if your woofers seem to be ok, except for rotted out rolls, the “odds are with you.”  But, it’s not a sure thing…

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Q:  The foam surround on my woofer has rotted out.  Can I replace the foam surround, myself?

A:  Yes, in some cases, but there are some pitfalls.  See the above question covering problems WE sometimes see, and, coming soon, Paul will add information about considerations for “non-pro’s” even when the roll deterioration is the only failure that has occurred.

There is very definitely an “experience” factor, in most driver repairs, and there are many “little things” (which can have a big effect) to look out for.  (We like to think our experience and attention to details are two of our strong points!)

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Q:  Does PR Audio sell recone “kits” to the public?

A:  We don’t sell recone “kits” to the public, because in order to do so, we’d get into either:

• 1) Shipping glues that fall under various “hazardous substances” restrictions, and the time involved with the paperwork / meeting shippers’ and gov’t requirements (which would be reflected in your cost) just gets out of hand…  Some of the proper adhesives are pretty specialized (esp. the high temperature glues, various treatments, etc.), and one can’t just run down to a hardware store to pick them up.

Or,

• 2) Selling pre-assembled cone-spider-coil assemblies.  Someone like JBL can do this, because they only have a relative few models to cover, some with common parts, and, more important, they have jigs (or just extra structures, for that matter) that they can build the cone-spider-coil assemblies on.  Since they use the same baskets for a lot of models, etc., they don’t have to have all that many jigs. But, for someone like us, we’d have to have a unique jig for literally hundreds if not thousands of different speaker (driver) designs that have been made in the last 50 years or so.  And until we got one of each model in, we would likely NOT have all the information to fabricate a jig for it’s recone kit.  One jig might handle several of JBL 12″ models, for example, but we’d probably have to have a shelf of jigs just for ALL the different 12″ designs JBL has had over the years.  So, selling pre-assembled cone-spider-coil assemblies is generally not practical or cost effective, either.  (Taken as a whole, in the speaker business, very few things are really “standardized.”)

And,

• 3) There is just no way to guarantee “like new” (or better) results unless we have a driver in need of repair in our own hands.  (See also the other information on this page.)

Again, There is also very definitely a significant “experience” factor, in reconing, and there are a lot of “little things” (which can have a big effect) to look out for.  (We like to think our experience and attention to the details are some of our strong points!)

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Q:  Does PR Audio sell “refoam” kits to the public?

A:  No.  As stated above, there is just no way to guarantee “like new” (or better) results unless we have a driver in need of repair in our own hands.  (See also the other information on this page.)

Again(!), there is very definitely an “experience” factor, in most driver repairs.  There are a lot of “little things” (which can have a big effect) to look out for.  (We like to think our attention to details, and long experience, are some of our strong points!)

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More info. will be posted on this page, soon.  (It’s not ‘rocket science’, but we want to get it right!!!) 

As for rocket science and a real need to “get it right” :

(Photo courtesy of NASA.  Click to enlarge.)