111db Posted June 18, 2003 Share Posted June 18, 2003 As I was messing around with my '86 Fortes yesterday it became clear to me just how mechanically underdamped and ringy-cuppy the plastic mid-horns are. A light tap on the floor or roof of the horn interior produces a loud and obnoxious pop, like tapping the bottom of a paper cup. I'm sure the Dynamat tweak recommended in earlier posts is the preferred way to correct this, but here's a dead simple compromise. Take a square or round cross-section toothpick and break the tips off to make it just over 1-1/2" long (for a Forte, anyway). Wedge the toothpick vertically between the floor and ceiling of the horn. You're done! The horn is now far more mechanically inert, as you can confirm by tapping the floor of the horn with a fingernail with and without the toothpick installed. Maybe it's just my imagination, but I thought the speakers sounded noticeably more mellow and sweet after the pick treatment, with less of a "loud whisper" overtone. Try this for yourself and let us know what you think. Don (who is foolishly considering building a pair of K-horns) Quote Link to comment Share on other sites More sharing options...
JohnA Posted June 19, 2003 Share Posted June 19, 2003 Hey Don, You've proved the horns ring and have reduced that ring by prestressing the horn. This is not a permanent fix, though. A better solution (now that you know you need one) is to remove the horn and apply rope caulk to the back side of the horn. The rope caulck actually absorbs vibration and converts it to heat, plus the extra mass lowers the resonant frequency (hopfully below the crossover point). Quote Link to comment Share on other sites More sharing options...
lovemyhorns Posted June 19, 2003 Share Posted June 19, 2003 Hi, Where would get this rope caulk and what brand is recommended. When installing, should it go the full length of the horn?? thanks, Jeff Quote Link to comment Share on other sites More sharing options...
STL Posted June 20, 2003 Share Posted June 20, 2003 Rope caulk is rope caulk -- don't worry about brand. Look for it where weather stripping is sold at your local hardware store. Quote Link to comment Share on other sites More sharing options...
111db Posted June 20, 2003 Author Share Posted June 20, 2003 On 6/19/2003 6:06:24 PM John Albright wrote: "The rope caulck actually absorbs vibration and converts it to heat, plus the extra mass lowers the resonant frequency (hopfully below the crossover point)." --------------- Hi, John. Yes, you are correct about why the toothpick makes the horn more inert, and also in your explanation of the effect of the rope caulk. (When I mentioned Dynamat I meant rope caulk; Dynamat is generally used for damping stamped steel woofer frames, duh.) I can see how the caulk would increase the moving mass and therefore lower the resonant frequency, and how a plastic (vs. elastic) material could provide some damping, but I am also concerned that with higher moving mass the Q of the resonance might increase and cause the horn to resonate as it is excited by WOOFER vibrations BELOW the crossover point. I design support structures for a living, and it is my experience that adding mass to an oscillating structure causes the frequency to drop and the amplitude to increase. Have you heard of anyone correcting plastic horn ringing by STIFFENING the horn body? I'm thinking of some transverse stiffening ribs or rings on the outer surfaces. The horn material is most likely ABS, and it would be easy to bandsaw some 1/4" thick sheet ABS rings to bond to the outside of the horn. G'day! Don Quote Link to comment Share on other sites More sharing options...
TBrennan Posted June 21, 2003 Share Posted June 21, 2003 Don----Indeed, some of the newer plastic horns used by Klipsch do have extensive stiffening ribs. A pair of tractrix horns from the pro line I owned had such ribs and pictures I've seen of the mid horn used in the Khorn show such ribs. Also the new Altec 511B horns, the horn evidently now back in production, show new ribbing. A friend of mine designs and builds his own tractrix horns out of a plastic material called foamcore. He glues ribs of the same material to the outside of the horns and the horns sound very nuetral. Quote Link to comment Share on other sites More sharing options...
Marvel Posted June 21, 2003 Share Posted June 21, 2003 Tom, Can't believe that someone would use foamcore for the horn. Still, I've also seen folks use paper mache, masonite (appied moisture or steam to bend). The foamcore has almost no mass to it, how would that work? Marvel Quote Link to comment Share on other sites More sharing options...
TBrennan Posted June 22, 2003 Share Posted June 22, 2003 Marvel---A horn doesn't need mass, it need only be rigid and the foamcore horns my pal builds are. PWK used to define a horn as "a rigid boundry for a column of air". The foamcore horns meet that definition. Quote Link to comment Share on other sites More sharing options...
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