Audio Proz Service and Sales

Reconing and Refoaming Woofer Surrounds

(Repair)

Sep 12th, 2015

We get a lot of calls about this matter. More and more music lovers are realizing that many older design woofers are still very competitive performing with modern parts and so it’s worthwhile to replace woofer surrounds. Personally, I’ve seen older Advent, HH Scott, some Infinity, the better original KLH, and especially a wide range of AR woofers that can perform better than some esoteric parts. Magnet, voice coil, and cone technology has made some great strides in improvement today, but most consumer-grade chain marketing speakers are certainly inferior to the great designs of the 60’s to the 80’s. To be clear however, tweeter improvements have been more remarkable due to the ability to wind more accurate voice coils and the availability of higher quality dome materials.

The important advice I can give is this: Although I applaud the hobbyist who will try “do it yourself” speaker edge re-foaming, this job is actually more difficult than it appears. In my experience I seldom (if ever) see it done correctly.

By the time the foam deteriorates, usually the voice coil centering spider has either bottomed out or the lacquer impregnated cloth is now off center. To do re-foaming correctly requires removal of the dust cap, insert a voice coil positioning former and a trained eye to know where the center of the voice coil falls in the magnet gap. Moreover, I see many foams which are incorrect and consequently inaccurate cone re-centering will result. A skilled re-coner knows how to shim the foam height and use the right foam thickness to ensure optimal cone vibration dampening.

Even more problematic is the fact that re-foam kits don’t address the correct edge angle of foam to cone and as a result, buzzing of the foam edge will occur. Again, an experienced re-foam tech will know which foam is truly appropriate. I will get annoyed when people say it sounds fine to them, but I hear severe foam buzzing or worse, an off center voice coil rubbing on the magnet gap. In time this situation will wear away the enamel coating of the voice coil wire and expose bare copper wire at the rub area, effectively intermittently shorting the speaker voice coil. Ultimately this situation causes the amplifier to work unstably, and often causes overheating. Then, yes, the amp will burn up.

In my opinion even an average re-coning tech will do a better job (from experience) than a hobbyist. I hope you will trust me on this matter, but if you consider yourself knowledgeable about speaker technology and you’re very careful, then you may get it done right. Good luck, and let us know if you do need help.

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