This post is a follow-up to my question about remedies for 511B horn ringing posted about a week ago.

I have made some modifications to my 511B horns and can report the following;

1) De-stressing by gapping the fins greatly reduces the 'theater type' sound (obvious lower treble dominant and sharp (dynamic?)mid-upper treble) they initially had, but leaves some residual glare and hardness. The sound jumps out at you as this range is crossed.

Note that after de-stressing, I could still easily detect vibration in the central area of the large gently curved portions of the horn bell, and in the throat area.

2) I applied constrained-layer damping material in 2 steps.

In the first step I covered the horn bell from behind the front mounting flange back to the narrow throat - this substantially reduced the glare and hardness, and added considerable definition/resolution.

In the second step I covered the horn throat, from the rear (driver) mounting flange up to the rapid horizontal expansion - this resulted in another gain in resolution, especially in the upper treble. Cymbals are now much more clearly defined, no longer just a textured 'pff'. And...the soundstage really opened up. It's a whole new ballgame. The sound quality is now very similar to that from my JBL 2446/2380's. Very smooth, dynamic and detailed, and lacking in tonal coloration. The small format drivers (Iconic Model 102-16) are a bit more agile though, so the sound from the 511B's is a little more detailed and more extended in the HF (w/o compensation). As a bonus, they present a nice wide and deep soundstage - on good recordings, the speakers are replaced by the recorded acoustic space. They do not quite diasappear like LS 3/5a's, but then neither do the dynamics. The JBL 2380 CD horns simply do not image. They do produce a very appealing 'they are here' (as contrasted with 'you are there') presentation.

The material I used was Dynamat Xtreme. Other similar products would probably work just fine, but the Dynamat was available locally. I used about 7 square feet of material. It took about 3 1/2 hours to make some measurements on the horns, layout the cuts on the material and apply it to the horns. Total coat: about $60 with sales tax. Worth every penny! As always, YMMV.

Thanks to everyone here for help, humor and encouragement.

Regards,

AstroSonic