but as long as you can lower the frequency to the point where its not in the midrange, thats the goal wouldn't you agree? You can't eliminate it.
like what?
Soup stone blocks can be machined easily and there are many speakers made of it
My bass box was done from round disks of 25mm (1") MDF. Pentagonic holes were cut and then discs were glued together. Top plate vibrates a little, or perhaps it is the whole thing? Inner volume is 25 liter (closed) and driver is SEAS L26ROY.
Mo measurements but knuckle test says "dead as rock"
My bass box was done from round disks of 25mm (1") MDF. Pentagonic holes were cut and then discs were glued together. Top plate vibrates a little, or perhaps it is the whole thing? Inner volume is 25 liter (closed) and driver is SEAS L26ROY.
Mo measurements but knuckle test says "dead as rock"
This is very interesting. Hence, are you saying that the screws were not rigid enough to restrain the panel? Would more screws have helped? Or was it just that the back was so large that any uniform motion was a problem? In this later case then even a glued back would have been a problem unless it was CLD, and even then CLD does nothing if the panel moves as a unit.
Yes, but if you make the material thicker you raise the frequency.
I'm not sure, but at least I would expect not only 2D- but 3D-resonances - like in every room or speaker cabinet. I don't know how this will affect sound radiation of the panel, but it will.
Can someone give an example of building a cab using constrained layer damping? What are the materials you are using? Are these commonly available in the US? For example, 1/2" MDF, damping layer (?), 1/2" MDF.
Maiky mentioned that the interface from driver to front baffle and front baffle to rest of the cab is especially important. What are good practices to deal with these interfaces?
Maiky mentioned that the interface from driver to front baffle and front baffle to rest of the cab is especially important. What are good practices to deal with these interfaces?
Enclosure thickness and mass help to a certain degree; as does shape. Single greatest influence of enclosure on sound is via driver. Sound coming back through driver membrane is many times higher than that from enclosure with any significant thickness/stiffness. Internal loading from internal enclosure reflections for wavelengths fraction of cabinet dimensions (and driver diameter) make for complex loading of driver membrane, and thus resulting radiation in terms of frequency, and radiation pattern.
Back pressure can influence cone breakup behavior.
Back pressure can influence cone breakup behavior.
Passive Radiator Subwoofer Systems Article By Jeff Poth
Pictures 6 and 7 (a little over halfway down) show a removable rear. Vibration does not seem to be an issue with the assembly shown, when judged by the crude "hand on it" test.
We did a couple flavors of it at Snell. For the XA Reference we used double thick MDF with Noise Killer Yellow between. That gave a distinctly deader panel with a dull sound to the knukle rap test.
All the lesser models such as the E5, K5, XA75 and XA90, used a double baffle with a neoprene layer (almost like a flat layer of bicycle inner tube) sandwiched between box front and baffle.
I tried softer compliant layers but they seemed less effective and also very susceptible to shorting by inadvertent contact.
I really like the Noise Killer type damping layer between MDF layers. I think 2 layers of 1/2" MDF, or even 10mm, would give stiffness, mass and damping all in a reasonable material.
Compliant woofer mounts as we used at KEF are also very worthwhile. The same caveat applies, there must be no metal to wood contact or the issolation effect is lost.
David
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The damping layer, in the case of the noise killer, is a type of non hardening adhesive. It isn't ultra strong but it will keep the layers together until the cabinet is completed. The nice thing about constrained layer damping is that you can put a lot of screws or nails through without messing up the damping. This isn't the case if you are trying to issolate two layers.
David
David
On my current mains, I (well, my cabinet builder) used two 1/2" layers of Baltic Birch, with a different brand of viscoelastic adhesive marketed for car-fi. Cascade or something like that? I couldn't find the Noisekiller Yellow stuff that David's suggested several times (including above) here. Is it as good? Dunno. It seems to make for a nice knuckle-rap, though.
Did the Snell in-walls use thinner baffles? I seem to remember a brochure that said two layers of 1/4" HDF with damping compound between.
Noise Killer Yellow was a particular product that we bought from a guy in Sweden, but that was 10 years ago. Not sure if they are still in business but they did sell to the car stereo crowd for a while. If you find something under another brand that sells to the car stereo market and makes claims for constrained layer damping use (as opposed to a damping goo to go on a single external layer), I would think the odds are good that it would suit.
The interesting thing about this was that it worked best with a very thin layer. We did salesmans samples of a slab of wood maybe 4 inches square. One sample with and one without. Toss them both on the desk and one clatters, the other clunks.
Yes, I'd forgotten about the inwalls that used aluminum backboxes and the damped baffles. It probably was about 1/2" thick. We had some trouble cutting the rebates for the drivers because the depth of cut was about right to go through the damping layer.
David
ps Rockford Fosgate seems to sell the Noise Killer products. Contractors use Green Glue that looks like a similar product.
The interesting thing about this was that it worked best with a very thin layer. We did salesmans samples of a slab of wood maybe 4 inches square. One sample with and one without. Toss them both on the desk and one clatters, the other clunks.
Yes, I'd forgotten about the inwalls that used aluminum backboxes and the damped baffles. It probably was about 1/2" thick. We had some trouble cutting the rebates for the drivers because the depth of cut was about right to go through the damping layer.
David
ps Rockford Fosgate seems to sell the Noise Killer products. Contractors use Green Glue that looks like a similar product.
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Yes, I tried Rockford Fosgate. Couldn't find Noise Killer on their website.
Green glue seems to be used extensively in home theatre installations for sound isolation in walls. It is quite expensive though. I have read suggestions for using Butyl caulking in place of green glue. Apparently, it's the same chemical, but green glue comes with a hefty price tag.
Regarding the use of screws: do you put them in after the adhesive has set? I'd imagine it would get squeezed out if the layers are screwed together when the damping layer is wet.
Green glue seems to be used extensively in home theatre installations for sound isolation in walls. It is quite expensive though. I have read suggestions for using Butyl caulking in place of green glue. Apparently, it's the same chemical, but green glue comes with a hefty price tag.
Regarding the use of screws: do you put them in after the adhesive has set? I'd imagine it would get squeezed out if the layers are screwed together when the damping layer is wet.
Butyl caulking is nothing like green glue, I have not seen any other product out there that resembles green glue in any form. I've used green glue and it works extremely well for speaker cabinets, the only problem is that it takes a long time to cure. The screws are put in when the damping layer is wet. What i did was put a bead of glue around the outer parts of the wood panel. I think screws would work much better, though.
some years back Earl Geddes suggested using "melamine glue" which is about $30 for a gallon jug from Grainger. I made some cabs with that, the glue thinly sandwiched between two 0.5" ply layers. I've never tried other stuff for mid layers for a full comparison, but the walls of that cab were impressively dead.
constrained layer
I used that Earl Geddes melamine glue tip when building some subwoofer cabinets. I used 2 layers of 3/4" MDF and the cabinets are very dead when using the knuckle wrap test. The problem with this technique is trapped air between the layers. I fabbed up the panels and cut driver and plate amp rebates after allowing the glue to dry a couple of days. The cut edges did show some voids which I filled with glue. I used many clamps and several plates from my dumb bells and still had the problem. I think that a vacuum bag system like used for fiberglass layup would be the only true solution. The next time I use the technique, I might try putting the panel in a plastic trash bag and using my shop vac to create a slight vacuum before I apply the clamps and weights.
I used that Earl Geddes melamine glue tip when building some subwoofer cabinets. I used 2 layers of 3/4" MDF and the cabinets are very dead when using the knuckle wrap test. The problem with this technique is trapped air between the layers. I fabbed up the panels and cut driver and plate amp rebates after allowing the glue to dry a couple of days. The cut edges did show some voids which I filled with glue. I used many clamps and several plates from my dumb bells and still had the problem. I think that a vacuum bag system like used for fiberglass layup would be the only true solution. The next time I use the technique, I might try putting the panel in a plastic trash bag and using my shop vac to create a slight vacuum before I apply the clamps and weights.
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