One I tried when doing R&D worked well. Two layers of HD3 bonded with 3mm sheet rubber. The rubber is usually used to water proof decks, concrete roofs etc. I used a contact cement to glue them together. The vibration energy didn't get through the rubber. Bad side was trying to fit the panels together. Only way to easily do that was to use corner sinks. These are heavy corners designed to stop any energy from going from panel to panel. Worked well but the corner had a tendancy to fix the two sides at the edges.
The attached pic is from the initial tests of using corner sinks just to explain a little better. Corner material was Jarrah, a very dense timber.
The attached pic is from the initial tests of using corner sinks just to explain a little better. Corner material was Jarrah, a very dense timber.
Attachments
An interesting paper on the subject of constrained layer damping is here..
http://www.me.vt.edu/unmanned/papers/Gallimore.pdf
This clearly shows that the energy dissipated by the constrained layer is proportional to the area enclosed by the hysteresis curve, and indicates how much typical polymers have to be strained to get them into the hysteresis region, much more than the walls of any speaker box I would want.
rcw.
http://www.me.vt.edu/unmanned/papers/Gallimore.pdf
This clearly shows that the energy dissipated by the constrained layer is proportional to the area enclosed by the hysteresis curve, and indicates how much typical polymers have to be strained to get them into the hysteresis region, much more than the walls of any speaker box I would want.
rcw.
NO.
For the Green Glue to be effective, you want there to be some space between the two panels, only attach them at the edges/corners.
Ideally, you would build two seperate shells seperated by lines of green glue spaced every couple of inches - the two seperate walls of the enclosures would not be firmly attached except at the corners.
The inner enclosure would be well braced.
Any particular type or brand you like? Do you buy the tubes that go in a caulking gun?
I was talking with the supplier of GreenGlue in Oz ,they made an internal cabinet then covered it with green glue then made an external cabinet to encapsulate the internal cabinet .The gap between the 2 layers was not greater than 0.5mm and both board's were the same thickness and material for CLD to work .
SikaFlex and LocTite make a similar product but minimum thickness needs to be 2mm .
For my own cab's I'm using 5086 alloy and ply .The alloy baffle's are light weight and very stiff no flex .
Cheers
SikaFlex and LocTite make a similar product but minimum thickness needs to be 2mm .
For my own cab's I'm using 5086 alloy and ply .The alloy baffle's are light weight and very stiff no flex .
Cheers
I use GE Silicone 1 which seems to set faster and has better adhesion than Silicone II. They come in a tube for a regular caulking gun.
It would be interesting to do a comparison between a CLD type panel and a one piece panel (but thicker). Using an accelerometer, measure the vibration from the inside of the panel and the outside on both panels and see if there is a difference.
According to rcw, the thicker, one piece panel with transmit less energy to the outside due to it's superior stiffness.
Speakerlab, here in Seattle, used to make their cabinets using a glued up laminate consisting of a 1/2 inch particle board (not MDF) inner layer, glued to a 3/4 inch plywood outer layer. They used mitered edges for appearance and to increase the area of the gluing surface.
Heavy, but very effective, as the dissimilar materials and thickness would serve to cancel different frequency ranges and modes.
Best Regards,
TerryO
Heavy, but very effective, as the dissimilar materials and thickness would serve to cancel different frequency ranges and modes.
Best Regards,
TerryO
Thanks everyone for all the input. FWIW I see the simple lamination of chipboard and ply as damping and will look to something more in the line of CL damping as has been suggested in many of posts with various innovative solutions. Largest panels are 750x600mm so I will need to see if this really justifies the design approach or whether a nearly as good result would be achieved from focusing on the bracing.
I took a look at Mason Industries web page. They manufacture acoustic vibration isolation materials to keep mechanical equipment from transferring sound and vibration into a building or in some cases keep the building from shaking things like pianos on the theater stage.
Sandwiches made from layers of natural rubber, cork, more natural rubber outside of all that stiffer materials to handle point loads. We do not care about point loads for speaker boxes.
It is not so much stiff next to flexible. It is the abrupt change of the speed of sound through differing density materials that causes the reduced or attenuated transmission of sound power levels through the materials. also consider that the driver may be vibrating the face of the box. There is a paper at linkwitzlab.com that discussed the use of vibration isolation materials between the driver and the box.
Materials that we DIY folks can use are cork ceiling tile and closed cell neoprene wet suit material, or floor mat, gypsum wallboard and birch plywood to look nice and be strong. Stick it all together with an airless spray of tack adhesive.
DT
All just for fun.
Sandwiches made from layers of natural rubber, cork, more natural rubber outside of all that stiffer materials to handle point loads. We do not care about point loads for speaker boxes.
It is not so much stiff next to flexible. It is the abrupt change of the speed of sound through differing density materials that causes the reduced or attenuated transmission of sound power levels through the materials. also consider that the driver may be vibrating the face of the box. There is a paper at linkwitzlab.com that discussed the use of vibration isolation materials between the driver and the box.
Materials that we DIY folks can use are cork ceiling tile and closed cell neoprene wet suit material, or floor mat, gypsum wallboard and birch plywood to look nice and be strong. Stick it all together with an airless spray of tack adhesive.
DT
All just for fun.
Rest assured that you're not the only one and yes, it would help if it were explained in an understandable manner.
There also seems to be a distinction being made between damping and constrained layer damping which is, to my mind, confusing.
Best Regards,
TerryO
3/4" Baltic Birch or MDF with braces is decent, better than typical Best Buy speakers...
But, if you want better than just "decent" cabinets then...
The combination of materials of sufficiently different "Q" + a separating layer of a viscoelastic damping material is very good. For example, let's say you want to make a spherical enclosure: one layer of aluminum + one layer of steel separated by some sort of damping material (such as Green Glue) is FAR better that either steel or aluminum by itself (I've tested this and found the difference to be well beyond subtle).
Two walls with the cavity filled with sand is excellent.
Two walls separated by a couple layers of "roofing felt" paper (only attach the walls together at the corner, if you nail/screw the two panels together, you'll defeat the effectiveness of the damping you would have otherwise achieved. This was tested by another gentleman who graphed the results and showed a large benefit to this type of cabinet construction.
But, if you want better than just "decent" cabinets then...
The combination of materials of sufficiently different "Q" + a separating layer of a viscoelastic damping material is very good. For example, let's say you want to make a spherical enclosure: one layer of aluminum + one layer of steel separated by some sort of damping material (such as Green Glue) is FAR better that either steel or aluminum by itself (I've tested this and found the difference to be well beyond subtle).
Two walls with the cavity filled with sand is excellent.
Two walls separated by a couple layers of "roofing felt" paper (only attach the walls together at the corner, if you nail/screw the two panels together, you'll defeat the effectiveness of the damping you would have otherwise achieved. This was tested by another gentleman who graphed the results and showed a large benefit to this type of cabinet construction.
If you deflect for instance spring tempered carbon steel and release it the energy taken to deflect it a given amount is returned when you release it, and the ratio of the stress to strain is linear, this is known as Hook's law.
In a material that has hysteresis however this ratio is not linear and the amount of energy returned is less than the energy of deflection, the discrepancy being dissipated as heat and / or molecular displacement, and this effect is also frequency dependent.
If you have a very small displacement you need a large resistance to this in order to get enough energy into the material, and the only polymers that have these properties are hard rubbers and plastics and such things as epoxy resins.
For these small displacements you simply cannot get enough energy into such things as the green substance, and if you put it between panels the damping you get is due to mass damping and decoupling at these small displacements, not constrained layer damping, since you are simply not pushing the stuff far enough into its dissipative hysteresis region.
If you design specifically for these damping schemes, you can come up with a design that
is really effective an not some ersatz non optimal combination of them.
Rcw.
In a material that has hysteresis however this ratio is not linear and the amount of energy returned is less than the energy of deflection, the discrepancy being dissipated as heat and / or molecular displacement, and this effect is also frequency dependent.
If you have a very small displacement you need a large resistance to this in order to get enough energy into the material, and the only polymers that have these properties are hard rubbers and plastics and such things as epoxy resins.
For these small displacements you simply cannot get enough energy into such things as the green substance, and if you put it between panels the damping you get is due to mass damping and decoupling at these small displacements, not constrained layer damping, since you are simply not pushing the stuff far enough into its dissipative hysteresis region.
If you design specifically for these damping schemes, you can come up with a design that
is really effective an not some ersatz non optimal combination of them.
Rcw.
Ok, now I get you.
But - I have another way of looking at CLD. I see it as being similar (in principle) to shielding on satellites against damage from hypervelocity particles. This shielding uses 2 layers - the outer layer will take the full impact of the particle and will most likely be pierced, the inner layer can then withstand the impact as the particles energy has been used up breaking through the first layer. The inner layer sustains no damage, incurs minimal stress.
So, the inner layer of the CLD system taking the brunt of the energy, being allowed to resonate and dissipate this energy without transferring (much) to the outer layer. Tightly coupling these layers together would defeat this action.
I'm I being clear?
But - I have another way of looking at CLD. I see it as being similar (in principle) to shielding on satellites against damage from hypervelocity particles. This shielding uses 2 layers - the outer layer will take the full impact of the particle and will most likely be pierced, the inner layer can then withstand the impact as the particles energy has been used up breaking through the first layer. The inner layer sustains no damage, incurs minimal stress.
So, the inner layer of the CLD system taking the brunt of the energy, being allowed to resonate and dissipate this energy without transferring (much) to the outer layer. Tightly coupling these layers together would defeat this action.
I'm I being clear?
Yes John you are being perfectly clear, but this is decoupling not constrained layer damping.
You can certainly use the cld scheme in the walls this case, but as I have pointed out whilst using a substance like green glue will provide useful decoupling between the two enclosures in a box inside a box scheme, it will not provide cld used in the walls themselves, (unless they are very thin and have a lot of movement).
cld damping for small displacements needs different materials, and at the moment I am attempting to find out exactly what they might be.
rcw.
You can certainly use the cld scheme in the walls this case, but as I have pointed out whilst using a substance like green glue will provide useful decoupling between the two enclosures in a box inside a box scheme, it will not provide cld used in the walls themselves, (unless they are very thin and have a lot of movement).
cld damping for small displacements needs different materials, and at the moment I am attempting to find out exactly what they might be.
rcw.
Well, I left out the obvious part - where the inner layer (the one that takes the bulk of the energy) is "constrained". The inner layer is not decoupled from the outer but is allowed to move and is constrained and damped by the lossy layer and the outer layer. This is the point of it, in my understanding, that the inner layer be able to flex into the lossy layer and not have this energy pass (entirely) to the outer layer. In my mind it doesn't matter how much energy is coming to bear on the inner layer, it will still react and the mechanism of the system will still reduce energy transmission through to the outer layer.
When the inner and outer layer are rigidly coupled, this loss will not happen.
When the inner and outer layer are rigidly coupled, this loss will not happen.
I'm sorry, but I have to disagree. CLD is a well know technology, even where the dispacements are small, like automotive floorboards, hoods, etc. It has nothing to do with a "hysterisis curve". The technique basically turns bending into shear for which all damping material are far better suited. A CLD panel is far better damped than a solid panel of equivalent thickness - basically its NOT "mass damping" because there is no such thing. Mass is mass and damping is damping - different things that should not be confused with one another.