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January 28, 2012

Fixing Old Speakers – The Common Woofer Foam Rot Problem

Audio Research freebie speakers

Audio Research freebie speakers

Got an old pair of speakers that don’t bark as well at the low end as they did in their younger days? You might be suffering from the dreaded woofer foam rot. Recently, I had been hunting for a good, cheap pair of speakers to partner with my newly repaired Hitachi receiver. I luckily found some free on Craigslist; someone just 2 blocks from me was giving away a great pair of 4-way Audio Research speakers with massive 12″ woofers, probably 1980′s vintage. They were “great”, that is, except that the suspension foam surrounding the woofers had almost completely decayed away.

Foam Rot

Woofer Foam Rot

This is the well-known “foam rot” problem seen in woofers and other high-compliance drivers of similar age. A few decades ago, speaker manufacturers started using a glued-on ring of shaped foam in place of the concentric corrugated cardboard surround on hifi speaker woofers, presumably to reduce distortion, especially at high excursion amplitudes. Unfortunately, the use of this foam has a recomplicating effect; it tends to decay away in 20 or so years, rendering the woofers useless. (The foam is apparently far from stable, which is good reason also to wear gloves when doing this repair; I don’t know the composition or the decay products.) Fortunately, there is an easy solution; there are many vendors of new, precise-fitting woofer foam, and the repair can be done quickly. (more…)

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