Surround Goop Rejuvenation Success!

[Geekstar]

While working on my 756B project, I experimented with bringing dead goop back to life using acetone. It worked well according to measurements.

Speaker 1 had very little goop left. Most of it evaporated or slipped through the wormhole into another dimension.

Speaker 2 had a thick layer of shiny goop. However it was hard and not sticky to the touch like it should be.

When I ran TS measurements with a woofer tester, I found that the fs of Speaker 2 was ~20hz higher than Speaker 1, on the order of 55hz vs 78hz. Impedance peak at fs was much lower on Speaker 2.

I suspected the hardened goop was the culprit so I tried to re-soften it by applying acetone with a paintbrush. I hit it numerous times at 10 minute intervals, then measured a noticeable drop in fs.

Noting that there is another layer of goop on the underside of the surround, I brushed that side a few times with acetone as well. After letting the acetone evaporate, I measured the speaker again and fs was even lower--66hz!!

I think I can go a bit farther with this technique but I thought it wise to hook up the speakers and let them play and loosen up for a while. I'll remeasure and, if necessary, do another round of acetone when I take the drivers out of the boxes to paint them.