Uniblob

Yes, it was fully disclosed. I bought the J100 from one of my best friends and in his words "this thing is a cannon, but I should mention, it has this weird patch inside...". My suspicion, as 62burst stated, was it was there for electronics that were never installed. The pic attached is a 1994 Gibson Gospel with on-board EQ electronics. The location of which is exactly where the foam rubber patch is located on the inside which to me makes sense as a damper to prevent rattling or undesirable harmonics of the components on the inside of the guitar.

I just stick my iPhone in the sound hole, strings off.

Yes! For all we know that guy could have worked there for six months and got fired for gluing weird foam rubber pieces inside all the J-100s!

Thanks for sharing those pics gearbasher, very cool. No, definitely not Velcro. A very thin foam rubber.

Just bought a beautiful 1994 J-100 and wanted to see if anyone had any information about a weird foam rubber patch that is inside on the upper top bout. The guitar has no electronics, but the patch is right at the spot where I have seen on-board controls on Gibsons of the same vintage. The patch is not concealing any damage at all. Using a very intense inspection light shows the wood grain totally undisturbed. And yes, the builder's name is written inside in pencil, Eric A. Luhrsen. Is it customary for the builders to write their name? I've don't recall seeing it in other Gibsons I've had (but I also don't recall ever checking!) It's a magnificent guitar and I have no concerns about the patch, really just curious if anyone knows the story.