dtximages Posted June 25, 2000 Share Posted June 25, 2000 I was thinking about all the mods I have done to my la scalas when it comes to dampening resonances. Nothing was ever really mentioned about the woofer horn itself. All you have to do is knock on the side wall of it to hear how empty and hollow it sounds. I love the sound of my la scalas but they can get real bloated in the upper bass and lower vocals when sent through the woofer. I made so external and internal braces for them to strengthen the sides and they sound better than ever. I could accually see the walls of the horn moving on certain bassy music so I figured that it had to do something to the sound. They now sound tighter and more accurate in the lower male vocals and seem to have more punch. I took some pics but I havent figured out how to put them on the bb yet so if you want them Ill mail them to you. Has anyone else tried this mod? I didnt mess up some technical aspect of the horn did I? If anyone else has tried it I would like to see your pics too if you dont mind. I also braced the internal "V" but it didnt make as much difference as this. This mod took ALOT of the boxy resonant sound of the woofer horn away forever. I hope. Any opinions? Chris Quote Link to comment Share on other sites More sharing options...
Klewless Posted June 26, 2000 Share Posted June 26, 2000 cls72 I think that would be an excellent mod. I have La Scalas and have been aware of the vibrating box. In my case, I have done none of the many mods available for my Klipsch speakers. Not that I don't agree with them; am just lazy! Consider that any of the energy created by the woofer that shakes the box, is returned as sound from the box. In other words, the result is at a different frequency and colors the original sound. Any effort to stop panel resonances is generally a good one. Good work. PS. That is one mod I actually plan to work on someday. ------------------ John P St Paul, MN Quote Link to comment Share on other sites More sharing options...
sunnysal Posted June 28, 2000 Share Posted June 28, 2000 I'm thinking this could also be valid for my k-horns..I have noticed that the bass box vibrates quite noticeably AND that the bass seems to have an overtone similar to my fist rapping the cabinet (I really do think I can hear a definite "note" to my rapping and that same "note" I can hear in much of my bass regardless of the music being played) anyone else feel the bass cabinet is coloring the bass? anyone have ideas on how to dampen the bass cabinet, or make it more rigid? this issue really rings true (forgive the pun) with me...regards, tony Quote Link to comment Share on other sites More sharing options...
arco Posted June 29, 2000 Share Posted June 29, 2000 Hi! I own Klipschorns and I was thinking about cabinet vibrations (and the resulting colorations...) for quite some time now. What I intend to do is bolt thick steel frames (say about 1cm thick...) on the side walls of the bass horn. This will theoretically make the panels vibrate at a higher frequency and, thus, partially solve the problem. And I say partially, because there is also the front panel...which I wouldn't touch, for aesthetic reasons. Would greatly appreciate if someone with engineering knowledge, could calculate for us the best - and lighter - bracing pattern... Quote Link to comment Share on other sites More sharing options...
Guest BobG Posted June 29, 2000 Share Posted June 29, 2000 If you are contemplating going to such lengths as steel plates, you might as well use a constrained layer damping. Between the plates and the cabinet, add a squishy layer of sorbothane or some such thing which changes mechanical energy to heat. Quite effective. Quote Link to comment Share on other sites More sharing options...
sunnysal Posted June 29, 2000 Share Posted June 29, 2000 bob, I wonder if you think the stiffness or the dampening approach is more valid? (especially considering I have k-horns, large expanses of wood walls!) I am not sure whther it might just be better to use some sorbothane sheeting (does this exist?) applied to the insides of the walls...or perhaps some additional wooden bracing...I am starting from the presumption that my feeling that the box is imparting some lind of bass overtone to the music and that this can be affected by reducing the drum effect of the bass enclosure...regards, tony Quote Link to comment Share on other sites More sharing options...
Guest BobG Posted June 29, 2000 Share Posted June 29, 2000 Here is a bit of info gleaned from one of our engineers on the topic of DIY damping of horns or panels: MATERIAL FOR DIY DAMPING Mortite wouldn't be bad... Mortite that's been handled for 10-20 minutes would be better... Whatever it is it should be heavy and mushy. I don't know what exactly what one might find at a hardware store, but it needs to be softer than roofing mastic, or any type of caulk (too springy) to do much good. A thick (1/4") layer of tar/sand topped off by "memory foam" would work very well. Sorbothane + contact adhesive + sheet metal would be good (constrained layer damping), though sorbothane alone wouldn't do much. For the less creative, adding tons of mass, without the damping, would be a next choice. Use construction adhesive full of lead weights... Some time ago, I worked on my Fortes, Academys and SW-12's. I first stiffened the cabinet walls by adding structural bracing made of 2x2's. All the area between the braces was covered with Dynamat. Stiffening the panels shifts the resonance higher in frequency and the Dynamat was intended to convert the high frequency resonance to heat. If you look at very high end turntable design, where vibration is the big enemy, constrained layer damping is typically employed if any damping at all is in the design. Klipsch is closely studying damping for a future project. Quote Link to comment Share on other sites More sharing options...
sunnysal Posted June 29, 2000 Share Posted June 29, 2000 bob, Quote Link to comment Share on other sites More sharing options...
Klewless Posted June 29, 2000 Share Posted June 29, 2000 Bracing group, I recently read someplace that bracing strips along the LENGTH of a panel is more effective that across it's width. Recommended brace was a rectangular strip of something like oak. It must be firmly attached with a glue better than the white/yellow carpenter's stuff typically found in hardware stores. They said use one of the available 2-part glues. No experience on my part here. Just repeating something I read and thought sounded reasonable. Call me untested ------------------ John P St Paul, MN Quote Link to comment Share on other sites More sharing options...
dtximages Posted June 29, 2000 Author Share Posted June 29, 2000 Klewless. I put extra panels of wood along the side walls of my la scala bass horns to try to stiffen them so that they wouldnt vibrate. I dont feel like that did much because when I would knock on the inside of the wall it still resonated and sounded hollow. The thing that worked best in the la scala mod is the 1x4 horizontal braces in the horn itself. That was my conclusion at least. Quote Link to comment Share on other sites More sharing options...
tonygeno Posted June 29, 2000 Share Posted June 29, 2000 Wouldn't adding internal bracing of the cabinet change the "tuning" of the cabinet since cabinet volume would be reduced by the volume of the added bracing? That said, I have heard that using threaded rod with large nut type devices at either end can be used to exert pressure against opposite panels inside an enclosure thereby stiffening the panels. Anyone ever try this? Besides, the rod takes up very little internal volume. Half inch threaded rod would probably be sufficient. Quote Link to comment Share on other sites More sharing options...
sunnysal Posted June 29, 2000 Share Posted June 29, 2000 tonygeno you read my mind! I thought if I took bobs idea of metal+sorbothane+adhesive to the walls surface and then took a threaded metal bar and built a wedging system I could reinforce the walls AND dampen vibration of a higher frequency...I´m going to work out some diagrams this weekend...anyone want to see the results? regards, tony Quote Link to comment Share on other sites More sharing options...
Klewless Posted June 30, 2000 Share Posted June 30, 2000 sunnysal, I'd like to see if you get any pics to post. Also I once built my version of La Scalas and fastened a 1x2 brace from the front of the "V" to the sidewalls. Seemed to work fine. I don't think that braces at the mouth would be any kind of a problem, unless they are awfully large. my thoughts......... ------------------ John P St Paul, MN Quote Link to comment Share on other sites More sharing options...
Guest BobG Posted June 30, 2000 Share Posted June 30, 2000 I assumed the concept was to add to the Outside of the horn. I can't suggest changing the functional surface of the horn. The Room Tunes company does some Really Cool stuff with tuning rods such as mentioned above. I think it may be tough by trial and error, but it really works. Quote Link to comment Share on other sites More sharing options...
dtximages Posted June 30, 2000 Author Share Posted June 30, 2000 Bob G. I have also done bracing to the inside of the "V". I wedged two 1x4s in the angled part and screwed them in tight with weather stripping to better the dampening. I dont think that the internal volume would be much affected because the la scala really doesnt use much tuning does it. Its just a horn. Not a box. I guess the "v" part is a box with a tuning freq. but does it really matter in the la scala? Quote Link to comment Share on other sites More sharing options...
Klewless Posted June 30, 2000 Share Posted June 30, 2000 cls72, I agree with your experiments. Adding a panel to the horn sidewall (inside or outside) which is still unsupported at it's exit would still vibrate! A horizontal brace across the lip of the horn mouth make sense (what I was suggesting earlier). A vertical strip on the lip (inside or outside) would be similar to trumpet horns which have a rolled edge to hold things together and help control vibration. Perhaps BobG's comments about constrained layer damping may apply to horn lip (perimeter) reinforcement as well. ------------------ John P St Paul, MN Quote Link to comment Share on other sites More sharing options...
lammers Posted June 30, 2000 Share Posted June 30, 2000 Why not put Dynamat UNDER another layer of Baltic Birch and use molding at the edges? And put some strips of Dynamat on the splines of the woofer basket. Now, somebody gimme a Corona with a lime wedge! Quote Link to comment Share on other sites More sharing options...
J M O N Posted June 30, 2000 Share Posted June 30, 2000 Tony, That's the exact reason I haven't really considered using internal bracing. One idea I recently had, mainly to test the bracing theory, was to get some "giant clamps" and put the clamps on the sides of my Cornwalls to tighten up the side panels and see how that sounds. The concern I have about doing this is that then the clamps themselves might resonate and produce sound. Quote Link to comment Share on other sites More sharing options...
sunnysal Posted June 30, 2000 Share Posted June 30, 2000 les, you da´man!...I think the birch idea is great! but I was thinking of adding the metal+sorbothane inside...bob, why not inside? it seems to me the 1/8" (max) wouldn´t make any difference to interior volume AND you wouldn´t have to worry about cosmetics (though les has a great idea!)...what problem could I cause? I am still going to work out a few ideas and post the drawing for comment...regards, tony Quote Link to comment Share on other sites More sharing options...
Klewless Posted July 3, 2000 Share Posted July 3, 2000 cls32, Based this thread, I went home this weekend and took out my RTA to see if I could detect any panel resonances in my La Scala. FWIW, my experiments were not strictly scientific (but were repeatable). Here are the results. I stuck the RTA inside the horn and tapped lightly with both my fingernail and my knuckle. I got similar results with the knuckle showing a broader pattern (more energy). I tapped lightly enough to keep the display within the range of the RTA. I observed with the RTA both inside the horn and right next to the outside of the cabinet (while tapping on the inside). The peak seemed to be consistent whether inside or outside, so I concentrated on inside measurements. The 100 Hz band barely responded. A sharp peak of (full scale) about 15 db appeared on the 125 Hz band. The next two bands 160 and 200 Hz also were part of the peak but at about 6 to 8 db down. Encouraged by all this, I then put a big clamp across the front of the La Scala. The 125 Hz peak totally disappeared. However a smaller but measurable peak appeared way up around the 250 - 400 Hz bands (which I did not investigate). This peak was about 6 - 8 db lower than the original 125 Hz peak. Then I slowly loosened the clamp while tapping and observing. At one point ALL peaks disappeared altogether. By the time I had the clamp loose, the original peak re-appeared. Obviously this does not speak for how strongly this peak is excited by sound from the driver, but it is definitely there. Your horizontal bracing seems to have merit. Of course, I have no clue as to the strength of my clamp or the accuracy of my RTA. I hope this helps. ------------------ John P St Paul, MN Quote Link to comment Share on other sites More sharing options...
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