I would expect 1/2" to be worse than 1/4" when it comes to damping loss because of the way CLD works but it will depend on the properties of the damping layer and the relative stiffness of the structural and constraining layers. With CLD the outer layer is not structural it is there to constrain the damping layer.
If you intend to glue your solid wood panels together as the figure suggests then you will have a rigid box of solid wood and it is likely to fail as mentioned earlier. However, so long as the movement doesn't cause the damping layer to become unstuck it should still work fine even if it looks bad. My suggestion above was to leave a gap as would be done with solid wood furniture, flooring, etc... But to repeat, I am not an expert with solid wood because I wouldn't consider making a speaker with it.
That looks the right kind of approach to me.
According to that post it sounds like it would be no problem to just put screws through the CLD sandwich. Surprises me a bit, most often it is said that anything that "breaks through" the CLD ruins the CLD effect to some extend.
My sandwich plan was this:
- 3/4" Plywood (about 18mm in reality)
- 1/16" Butyl sheet (about 1.6mm)
- 1/2" or 1/4" hardwood (~13mm or ~6mm)
I am struggling a bit deciding whether Butyl would be better than Neoprene, and whether I should maybe double the thickness of it. Any thoughts?- 1/16" Butyl sheet (about 1.6mm)
- 1/2" or 1/4" hardwood (~13mm or ~6mm)
The durometer of the Butyl is 60A (medium hard), the neoprene is available in 30A, 40A, 50A, 60A, 70A hardness.
The back and front are not in any way connected with any other hardwood panel. The sides, top and bottom are connected in the graphic, but I will probably leave a small gap just to calm you down
. No, seriously, it may be a good idea to leave a gap.
Have you considered using soft polyurethane adhesive to attach the panels, it's like marshmallow and works well. Screws are not required, or desirable.
These work best for the thickness when both sides are the same stiffness.
I would go with a product that has a durometer of 30. Neoprene and sorbothane both are available. Remember that attaching these type of layers requires bonding with an adhesive with a high shear strength. Can be done with clamps, lots of clamps or the prefered method, vacuum bag it. This prevents any air bubbles being trapped between layers, nullifying the intended result.
Titebond mastic, liquid nails, soft epoxy, a mess of things can be used for cld. The best suggestions are not normally inexpensive eg sorbothane... at the very least use this for the gaskets all up for best results.
Titebond mastic, liquid nails, soft epoxy, a mess of things can be used for cld. The best suggestions are not normally inexpensive eg sorbothane... at the very least use this for the gaskets all up for best results.
Thanks for your help.
With the gasket, you mean the gasket around the driver?
Can you recommend any particular adhesives with a high shear strength?
It's kind of hard to search for this... I was going to use 3M 4799 which is specifically for gluing rubber-like surfaces, but I don't know what shear strength it has.
Maybe I'm a bit late to the party but damping works best on stiff and light panels so minimizing the thickness of the inner box works better. For the enclosure I built I used a light stiff inner box of 6mm ply and 18mm ply braces. Then I glued damping material (bitumen roofing, other stuff is probably better but a lot more expensive) to the inside and outside. Then I glued the 18mm ply on top of this. This leaves you with a very stiff 6mm ply inner box that is damped on the inside and you get some CLD between inner and outer box. The large difference in thickness (weight) of the outer box makes it unlikely that it will get excited by the light and very well damped inner box. For best results make sure there is no mechanical connection between baffle and outer box.
Floor tack is also an option for cheap glue, it sticks to pretty much anything and stays visco-elastic.
Floor tack is also an option for cheap glue, it sticks to pretty much anything and stays visco-elastic.
Hmmmm... just bought a sheet of 18mm plywood today.
I was a bit worried that 9mm would not be rigid enough (despite a lot of braces). I guess it would, but most often I read that more mass is always better...
Ideally I should make the outer layer at least a bit thicker, and I probably can; even go up to 3/4".
Could you share how you attached your drivers to your CLD enclosure? It seems to be a bit tricky if one wants to avoid a mechanical connection between the inner and outer layers.
I didn't use CLD on the baffle, I glued it to the inner box and made sure there is a space between outer box and baffle (1-2mm). I only used it for the mid enclosure. For the bass I used lots of bracing hoping to get the resonance frequencies above the passband. Here are some pics:
http://www.diyaudio.com/forums/multi-way/287929-achilles-fir-4-way-4.html#post4649751
Increasing stiffness raises the resonant frequency and it's Q. If you increase mass you need more energy to excite the resonance (and probably increase Q) but it will take longer for it to die down.
Damping doesn't work as well on heavy panels because if they start moving they have a lot of energy in that movement. The energy loss that the damping provides is related to the movement, more movement more energy loss.
So ideally you would want as light as possible and fairly stiff for the inner box. The small bit of energy in the movement of the inner box (small because it is light and it stays small because it is well damped) will not be sufficient to excite movement in the outer box and there should be a big difference in resonant frequencies between the well braced light inner box and the thick heavy outer box.
http://www.diyaudio.com/forums/multi-way/287929-achilles-fir-4-way-4.html#post4649751
Increasing stiffness raises the resonant frequency and it's Q. If you increase mass you need more energy to excite the resonance (and probably increase Q) but it will take longer for it to die down.
Damping doesn't work as well on heavy panels because if they start moving they have a lot of energy in that movement. The energy loss that the damping provides is related to the movement, more movement more energy loss.
So ideally you would want as light as possible and fairly stiff for the inner box. The small bit of energy in the movement of the inner box (small because it is light and it stays small because it is well damped) will not be sufficient to excite movement in the outer box and there should be a big difference in resonant frequencies between the well braced light inner box and the thick heavy outer box.
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