Remember this is a 2 year-old thread Mr. 1201 has responded to. He is not addressing any specific current problem, but speaking in general about tweeters and squawkers. Most SEOS designs don't used a mid-range, so I'm not sure the purpose of his comments.
The Klipch RF-7 he commented about does have a well known high-end resonance sound, but it also has a well-known fix, and it has nothing to do with the horn. The RF-7 problem is taken care of with a resister.
In my view the SEOS waveguide and the older Klipsch horns have very different design and resonance characteristics. The SEOS does NOT need damped. It is inherently MUCH thicker and the horn surface area is much shorter. It just doesn't vibrate like the Klipsch horn.
I damped the horns in my Klipsch CF-4's and a difference could not be heard on a listening test. There was a difference in the knuckle rap test by about a third of an octave, but it made no difference otherwise. The harshness I heard was really well dealt with by adding a relatively small amount of polyfil, and I believe most people here would be able to A/B my CF-4's and tell which sounded better, with or without the polyfil.
The 12" SEOS with DNA-360 sounds EXACTLY like the Klipsch CF-4 horn, I interchanged them in the Klipsch CF-4 and no difference could be heard, with each using the CF-4 cross over. Here is a detailed comparison between the two:
SEOS 12 vs Klipsch horn - I did a bad thing
: The larger Klipsch horn has been damped with 11 oz of pure Silicon seal in clear.