What you're seeing may be Moretite window caulking. You can Google. Out of the box it looks like a roll of ribbon cable (though bigger). When used as caulking you unwind a single "wire" of the ribbon cable and have a string of caulk about 1/8 inch in diameter which can be pushed into the gap between a sliding window and the larger frame, or any long, thin gap. It is probably made of clay and some sort of low volatility oil or glycerin. Probably like modeling clay.
The idea that the Klipsch mid horn needs damping, even more than provided by screwing the mouth to the front plywood board, has been around for a while. People would apply Moretite in strings or multiple width strings (strips).
I did not put any credence in this. Modifications are like belly buttons; everyone has one. And the modifier always finds that their mod was an improvement. They never find the mod was worthless or did harm. Cynical me speaking.
You should look at the four-part tour of the Klipsch museum with Jim Hunter on YouTube. Near the end he shows the mold used to cast the K-400 aluminum horn. Very impressive.
In 1987, Don Keele (big name in audio engineering) was working for Klipsch and designed the K-401 horn which is made from structural plastic (or resin perhaps). I've never read the reasons for the re design. Was it cost, or performance, or both?. It does feature some large rings of material which should increase strength and maybe damping.
Look at the History or the Klipschorn on the main site. These technical articles are easiest to find on the website map. There is a lot of interesting material.
In any event, there is reportedly a slight improvement in distortion in the K-401. (I'm sure a lot of people cried, "What are you doing with cheap plastic.) Now whether that is related to resonance the history does not say. But cynical me has to backtrack and say that maybe there is a corresponding slight improvement in distortion when material is added to a K-400. So it is not just a belly button modification. Smile.
Edited by William F. Gil McDermott, 27 October 2013 - 04:58 PM.