sticky stuff on vintage polks

leftwinger67

I was wondering what the substance is that Polk uses to get that sticky field on the speaker cones of the vintage speakers. Not sure of the modern ones, just never touched any. What I was thinking going way back in my youth I used to build balsa wood airplanes and cover them w/ modeling tissue and to stiffen them up used what was called clear dope. Problem w/ this is I think it did dry to the touch so you could paint afterwards. It's been so long I don't remember either way. Anyone know what they use and is it used so the cones do not dry out?

westmassguy

Lew, if memory serves, the early drivers from the 70s were paper cones which Polk modified by hand with a special doping that made them tacky. The later vintage drivers were also paper cone, but had a plasticized coating on them, which Polk then applied their secret doping sauce to. They were called Tri-Laminate (three layers versus two for the originals). The purpose was to reduce unwanted resonances. They also improved the voice coils on the later models

leftwinger67

Dave, for unwanted resonances, that's pretty interesting that they even considered that back then. I guess it's goes along with using butyl surrounds to prolong the driver's life So it's for sure a proprietary treatment. I just thought it was a way to somehow keep the cones from drying out. We know foam rots but truthfully never heard of cone rot unless it got wet so there goes my theory.

westmassguy

Paper cones do dry rot. Coated cones last longer. I re-cone a lot of paper/pulp cone drivers from the 50s through the 70s. Also depends on environmental conditions, humidity, direct sunlight/UV rays, how they were stored etc.
Some of the older woofers also had rolled paper voice coil formers which collapse due to dry rot.