In Reply to: Re: well damped 511's (and structural mods) posted by Wayne Parham on March 11, 2002 at 21:43:08:
Wayne, I've seen at least one reference where a guy removed the sectoral fins completely, but left the bell lips...said it was not worth the many hours labor involved, and he had access to full boiler makers tools, grinders, etc.
In the spirit of max benefit/least effort or $$, just cutting a slice out, and caulking is great. And most of these things, especially the cheaper ones offered, do need a coat of paint to look nice. Let the wife pick the color, match the decor, etc. Putty NEVER passes the WAF test, so that would be a small damping benefit, but cost you from the extra spousal static...
Anyone considering powder coating might want a milling machine or something similar used to make the cuts, for a cleaner final appearance...the rtv can be black(usually), but clear looks OK too.2035 update...levels match pretty well using "12 dB Pi pad", 1.0mH/10uF LP w/ 4.4 ohm/10uF zobel...average LF level from 100 to 1000 Hz. was flat +/- 1 dB; from 2 to 11 kHz. the HF averaged about 1/2 dB lower than the LF, and from 8 to 16 kHz, HF averaged 1.5 to 2 dB hotter than from 2 to 11 kHz., and varied +/- 2.3 dB's average. HF F10 estimated somewhat more than 17 kHz...these were measured with the 4 Pi on the floor, and the mike about 2 meters away...mike height adjusted to put it in the "line of hearing" from the middle of the two drivers to the listening position, 12 feet away. hf readings averaged for the 8 to 16 Khz. response were "corrected" per data from a net posting.
Since I need to go in and replace the port tubes with shorter ones, I will "boost" the overall HF by about 1 dB, getting it 1/2 dB hotter, rather than cooler than the LF. And seal the HF horn flares to the front baffle...did not see puffs of air, but the newspaper slid under one end of each H-290, gotta be a leak there! a machinist straight edge says the H-290's are not flat...at least the fronts aren't! Drivers are sealed to the rear of the horns with a "certainteed" elastomer plumbing gasket...about 2.75 od, they just fit in between the two bolts. These are "done", and sound great...I'm just putting on the "auction wax" for that last 1% of "shine". Sam
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