I put my front to back brace from the front panel, off centre, between the woofer and the midrange horn in the Tangents. The wood there is a thinner piece. I'm not sure if it adds much damping to the front panel, but there is a good sized plywood and sponge pad on the back panel. Putting it on the back of the woofer could be done in a non-permanent fashion by using your design except for the piece that goes from the back of the cabinet to the back of the woofer. The piece that extends forward to the back of the woofer could be attached to your brace structure in the way you usually attach it, and a plywood and sponge pad could be used against the back of the woofer. That would make the woofer fully removeable.
I didn't consider the venting of the woofer. The sponge pad placed on the magnet assembly could be notched to provide air flow. You would need to create a channel in the sponge, which should be easy to do. On the other hand, attaching Earls bracing to the front panel near the woofer should help keep the woofer from moving because it is rigidly attached to this panel.
Earl - air enough - in the case of vented motor assemblies (not all are), any longitudinal bracing member is either offset or notched to prevent blocking the vent. Attached is a photo of early parts dry fit stage of a build for an 8" full range unit. Note the markings indicating "driver goes here". In this particular case, the rear panel was later set on cleats to be removable for adjusting of internal damping material fill levels by ear.
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I haven't built a full cabinet for a very long time now. And looking at the above photos, I realize what a crappy job I did. In my defence, it was a cabinet design provided by the driver manufacturer. I have been toying with the idea of of building new cabs for the drivers in my La Scala speakers. The La Scala cab side panels are not braced at all and vibrate. It would be interesting to do a La Scala cab using the ideas in this thread. I would do it as two cabs. The doghouse in a La Scala could be built as an isolated cab within a cab using Earl's method.
Earl, have you tried making cabinet walls using your method? For example, could side panels be made up of two full pieces that overalp? One piece of the side panel
could be attached to the front panel, and the other part of the side panel could be connected to the rear panel. The top and bottom panels could be attached to the rear and front panels, or the side panels. There are a number of possibilities for attaching overlapping panels. I don't think it would require full panel overlap to have it work. Also, I don't think you would need to do all the panels.
could be attached to the front panel, and the other part of the side panel could be connected to the rear panel. The top and bottom panels could be attached to the rear and front panels, or the side panels. There are a number of possibilities for attaching overlapping panels. I don't think it would require full panel overlap to have it work. Also, I don't think you would need to do all the panels.
The memory foam looks like a nice idea. But then again I am not sure if it does a lot. This stuff is "slow", it takes a few seconds to adapt to changes in how much it's squeezed together. Audio frequencies may be to high to be absorbed by the memory foam. Some tests comparing the bracing with/without the memory foam might be useful, like here.
mbrennwa: I remember seeing your tests a while back. Great job on it by the way. The memory foam is compressed by the plywood plate by whatever degree you choose to compress it. It could be lightly pushed down, or heavily, and the amount of compression is varied by the thickness of the foam prior to it being squeezed by the plate. Also, memory foam is just what I used in the one example that I produced. The layer that is squishy and gets squished between the plywood plate and the side of the cabinet could be almost anything that you feel would do the job of absorbing/damping vibrations. It could actually be a mixture of materials. For example, four silicone pucks glued to the plywood with memory foam between and around them. The plywood board could be squeezed down until the silicone pucks are squeezed between the plywood and the cabinet side. The memory foam would also be compressed depending on how thick it is applied. I used memory foam because I had decommissioned a mattress topper and had a large sheet handy. That said, it is also dense and heavy for foam, and its mass alone helps dampen vibrations as compared to something lighter. You seem to have all the apparatus required to test my method. I don't have all that cool stuff handy. I just knocked and listened. My bracing seems to do the same thing that you observed. The knock has a higher pitch with the bracing, and it is less loud and lasts a shorter time.
The plywood sheet can be whatever size and shape you want. When I cut the pieces, one speaker got longer single side plywood rectangles instead of two smaller ones. I cut slots in the plywood piece, and used different thicknesses of foam in different areas. This drawing is roughly what it looked like. The top drawing is looking at the foam on the plywood board from the foam side. The second is a profile prior to squeezing. This is all more or less and from memory. The plywood that I used has some flex, and the foam being different thicknesses flexes the plywood at the thinner connections where it has been cut. This applies pressure unevenly across the surface. The plywood itself also acts as a springy damper because it too has some flex. This flex can be provided by either using thinner more flexible plywood or by cutting slots in thicker material, or a combination of both. This is just a whole different thing than a regular brace. It's primary function is not really increasing the rigidity of the cabinet.
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First it is important to understand what it is one is trying to do. I try and dampen the cabinet walls with CLD and damped cross bracing. The two largest panels, the front and back, are the biggest concern since they have the largest area, so I use CLD on those. My cross bracing is meant to dampen the side walls and the front to back motion of the largest panels. The top panel is too small to be of much concern and the bottom is ridged from placement. Your designs do not dampen either of the front/back panels, so they would not suite my needs. They will dampen the side panels well, but those are of a lessor concern.
The way its shown the cabinet would actually grow and shrink under the internal pressure. This is usually not a good thing since now the cabinet is radiating sound as a monopole, which is very efficient. This effect would be very well damped however so it might not be a major issue. I would expect it to act like a box larger than it really is that would increase the driver Q.
Earl: Just an idea. I always figure its best to throw it out there and see what smart people do with the idea. Lately I've done a bit of thinking about the possibility of using "'soft" cabinets. My thoughts were that an appropriately soft cabinet would serve to dampen all cabinet resonances. I didn't really consider the flex of the cabinet creating issues.
"Soft" maybe a little too extreme, but I also believe that too hard is not right either. Rigid enough to not be too bendy and very well damped is what I have tried to achieve for decades.
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