Originally Posted by Steve Hanna
If I'm fully understanding CLD, the constrained elastomer layer being sheared by the vibrations of the rigid constraining layers absorbs the energy of the vibrations reducing the vibration amplitude. Shearing forces would be lateral in the constrained layer. Differences in the constraining layers would enhance this shearing property in the panels. Adding CLD would add mass that could lower the frequency, but the 2nd contraining layer might also stiffen the panel and work to raise the frequency. B&W's flagship cabinets are very ridgid and dead. Knuckle rap test sounds like knuckle bones only. They do use CLD techniques, but mostly extreme bracing. More than most of us would be willing to implement. They also have a lot of proprietary tech and mesuring equipment. I'm a big fan, but not spending the ridiculous amounts asked for new or used B&W speakers. Check the prices for 30 to 40 year old speakers with kid dented drivers lol.
Hi Steve. I think most of what you said is right. However there is some debate about the different materials part. I read the exact opposite in some fairly old engineering books and papers. I asked Dr Geddes and a friend who engineers satellite parts. They both said they believe that old belief came from a need to be able to model and predict behavior and having same material for constraining layers makes that much easier. That isn't an issue today. Dr Geddes felt that different materials might have the advantage of non-identical coincident frequencies. That would certainly be a good thing.
Based on what I've read and measured from an accelerometer, it seems the effect is mostly noticeable at the point of resonances. Both the coincident frequency and panel critical frequency. It has less and sometimes no effect at other frequencies, especially below the critical frequency.
From what I was told recently, doubling the layers makes a material 8 times stiffer! When in a CLD panel that isn't true and for the purposes of estimating, it's more like 4 times stiffer if both layers are a like material. I've found a few articles testing this and it seems the exact amount can vary a lot, some were only slightly stiffer than a single layer and others were close to the full 8 times stiffer.
I actually think Magico and Wilson have some of the most advanced enclosures around. B&W has claimed a lot of incorrect things that they argued were proven in their lab but later seemed unsubstantiated and proven wrong. They made a big thing about dimpled ports but that was later proven to make things worse not better. They had a speaker with a funky shaped interior to diffuse sound but that too was later shown to make things worse and not better. Their bracing techniques have been tested as well and better approaches have been shown. Given what literature exists on CLD I also think they misuse it in their speakers. I used to lust after 800 series speakers but as of late I've lost respect for their engineering.
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