Something that might be worth trying if you live in house that has a chimney that is no longer used for open fires, would to use the chimney,
(assuming that it was capped clean and vented) as your infinite baffle. The advantages of length and solidity of construction would offer good benefits requiring only a circular hole for the driver in a solid timber baffle to fit into the fireplace.
A stone built chimney would be especially good as the inside would have an extremely irregular surface that would help prevent standing waves of any kind.
Has anyone experimented with grades of "wire wool" as a damping medium?
(assuming that it was capped clean and vented) as your infinite baffle. The advantages of length and solidity of construction would offer good benefits requiring only a circular hole for the driver in a solid timber baffle to fit into the fireplace.
A stone built chimney would be especially good as the inside would have an extremely irregular surface that would help prevent standing waves of any kind.
Has anyone experimented with grades of "wire wool" as a damping medium?
Interesting, but what I'm saying is that the walls of the speakers are ringing like crazy, being plywood, even with the bracing. It's stiffer, lighter and typically resonates much higher than MDF.
The concrete, having it in the bottom, or on top, or not at all, is probably having very little effect on the lower midrange ringing - it is the plywood.
The box needs to be coated with a heavy, low rebound rubber material to damp vibrations in the walls. Or laminate on a layer of 1/2" or 3/4" MDF.
More stuffing or changing the shape or adding weight will not help (much).
Think of a plywood box like a metal tuning fork. Hit it, and it's going to want to ring for some time. Now, dip that fork in a rubber coating - it will ring for far less time.
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I'm sure it can be designed to not ring, but the material itself rings. Also, the higher ply count, less ringing, but less stiff, from what I've seen.
I prefer 5-ply birch because of the exceptional stiffness, but it must be damped, for which I used rubbery roofing mastic. This was for a sub. Much stiffer than MDF, and lighter. It pings but doesn't ring and can't be localized. Ported, no stuffing, slat bracing.
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All material rings. The key to my designs is to push the (potential) to ring up high enuff that it is very unlikely to ever get excited
It is then either ~7mm ply, or cheap stuff if thicker. The stuff we now use has 13 plies in 15mm.
The transition between every ply represents an impedance mismatch which creates a lot of damping.
dave
Whatever the 3/4" 5-ply birch is that they sell at home depot. It was stiffer than the many-ply stuff they had. Much stiffer than mdf. Just my limited experience.
I should clarify resonating vs. ringing.
Boxes will resonate at a certain frequency, and it's a good idea to have this above or below the pass band, and that the box is stiff so the resonance is minor.
However, you can impact a box (with a bass note) and it will ring at it's resonate frequency, even though it may be out of the pass band. It's preferable that the box is well damped as to have the resonance decay as quickly as possible. A fairly stiff box that is not well damped will ring.
AFAIC resonating = ringing
Foreign to my experience. What resonant freq do you refer too?
dave
Dave me?
We have recently switched from Baltic Birch to Murphy ply (made in Oregon, 2 extra plies for 12/15/18 mm vrs BB, higher quality, and maple face veneers).
dave
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Thanks for all your comments.
Clarification about the bass bin construction: the internal panels toward the rear are 3/4" MDF, the front ones are 3/4" ply. All of the exterior sheathing is 1/2" ply, glued and nailed to the interior. Whole thing is glued and screwed, with every joint cleated, and it's braced to handle trucks driving over it. There is a solid cross (horizontal) brace not shown in the pic. All interior surfaces are lined with 1/2" thick heavy felt. No panel is more than 10" wide (most are much smaller), so I can't see them "ringing" very much. Baffle, top, and bottom are two layers of 3/4" ply. The outer top panel "floats" on a layer of Dynamat between the ply layers (with no nails or screws between them, only glue, so it is true CLD), so it does not transfer ANY vibration to the upper cabs.
There is not an attached concrete base. I apologize for not being clear. Concrete was poured into the bottom of the cab (inside the box), sloped to be thicker toward the rear, and thoroughly mangled to roughen the surface while setting up. It looks like a dog chewed egg carton foam, but concrete and irregular.
Each bass cab weighs 70 - 80 pounds. I wasn't fooling around when I built these, and I don't think they're contributing to the coloration I hear. In fact, they sound pretty good in the midrange when run without the xover. Cannot readily hear ringing (I'm not saying it doesn't; I can't readily hear it, which is what matters) when playing the bass crossed or full range, and I don't feel much vibration of the walls, even with very loud bass playing.
Peace,
Tom E
Clarification about the bass bin construction: the internal panels toward the rear are 3/4" MDF, the front ones are 3/4" ply. All of the exterior sheathing is 1/2" ply, glued and nailed to the interior. Whole thing is glued and screwed, with every joint cleated, and it's braced to handle trucks driving over it. There is a solid cross (horizontal) brace not shown in the pic. All interior surfaces are lined with 1/2" thick heavy felt. No panel is more than 10" wide (most are much smaller), so I can't see them "ringing" very much. Baffle, top, and bottom are two layers of 3/4" ply. The outer top panel "floats" on a layer of Dynamat between the ply layers (with no nails or screws between them, only glue, so it is true CLD), so it does not transfer ANY vibration to the upper cabs.
There is not an attached concrete base. I apologize for not being clear. Concrete was poured into the bottom of the cab (inside the box), sloped to be thicker toward the rear, and thoroughly mangled to roughen the surface while setting up. It looks like a dog chewed egg carton foam, but concrete and irregular.
Each bass cab weighs 70 - 80 pounds. I wasn't fooling around when I built these, and I don't think they're contributing to the coloration I hear. In fact, they sound pretty good in the midrange when run without the xover. Cannot readily hear ringing (I'm not saying it doesn't; I can't readily hear it, which is what matters) when playing the bass crossed or full range, and I don't feel much vibration of the walls, even with very loud bass playing.
Peace,
Tom E
Yep, contact microphone or even an old phono cartridge. Waterfall plots are pretty but hard to interpret. Simple response plots to see the frequency and severity of the various resonances would be a good start.
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