Removing melted rubber gasket from fiberglass

[da na]

The high-frequency horn on my Altec Lansing Voice of the Theatre cabinet needs a bit of cleaning, a large amount of dust and residue has built up inside the throat from 70 years of use. However, I cannot get the fiberglass horn separated from the compression driver. The two are bolted together with three bolts, but after removing the rusty nuts from each bolt, the horn won't budge. I would typically assume that the cause would be a screw-mounted horn, but I don't see how the driver could screw to the back if there are already three bolts on the driver connecting the two. Rather, I believe this is due to a rubber gasket being between the horn and driver. Seems like the rubber, after decades of being in a non-climate-controlled area, has fused the two parts together. The driver weighs a solid 20 something pounds, but its weight alone is not enough force to break the seal of the gasket. I would hate to shatter the ancient fiberglass of the horn - it feels quite thick and sturdy, but is also well over half a century old, so I'd rather be careful.

I tried inserting a butter knife to pry the two apart, but the knife broke in half when I pulled upwards - so clearly I need a sturdier metal implement that is still thin but perhaps has more surface area. Should I try applying heat or cooling down the area first? Maybe pouring a solvent (that wouldn't eat through fiberglass or strip the finish off the metal driver) around the edge of the gasket before beginning?

[manikyath]

isopropyl alcohol is a fairly safe place to start, just a few drops on one part of the rubber and see if it releases.

past that, hairdryer to the point it's just barely too hot to touch can be done too. dont go too far with heat though, you'll damage things very fast with too much heat.

[it_dont_work]

Start with wd40 as its easy to clean off with regular dish soap. Then try some silicone spray which will help rehydrate the ruber, again can be cleaned with soap and water.

 

Then if that doesnt work, try acetone, 50/50 with water at first, it'll dissolve the rubber. But try a test patch because its likely to discolour.  For the love of god also dont get it on the cone/rubber

 

This is basicly the method we used to use on PA and line array when rebuilding inhouse systems at venues 

[da na]

4 minutes ago, it_dont_work said:

Start with wd40 as its easy to clean off with regular dish soap. Then try some silicone spray which will help rehydrate the ruber, again can be cleaned with soap and water.

 

Then if that doesnt work, try acetone, 50/50 with water at first, it'll dissolve the rubber. But try a test patch because its likely to discolour.  For the love of god also dont get it on the cone/rubber

 

This is basicly the method we used to use on PA and line array when rebuilding inhouse systems at venues 

Luckily don't have to worry about getting any on the cone, a piece of the driver assembly extends a few cm into the horn. 

[it_dont_work]

Just now, da na said:

Luckily don't have to worry about getting any on the cone, a piece of the driver assembly extends a few cm into the horn. 

It's worth saying for cosmetics etc, I worked mostly in industry so if the above didn't work a pry bar did. No one cares what it looks like when its 30ft from the stage 

[Rocketdog2112]

Can you saw through and separate the two pieces with something like a guitar string?