You've been reading elsewhere, that's good. Panzerholz and Permali are so well damped that you would not need the CLD of the Swedac DG A2. But if you want overkill..... And as Andy stated in Post #149 of this thread, you have to be aware of the frequency ranges that excited the enclosure walls.
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Great. So I'll shoot for high stiffness for the midbass as well. Heavy bracing plus thick MDF walls should do well.
So the big deal with dampened materials is for the midrange and tweeter, or for an enclosure where all drivers will be housed in one cabinet I guess. This simplifies things. It doesn't often happen in this hobby!
Here is a link with some info regarding cabinet material design.
Qboard | Qln
I have worked with this for over 20 years
When we compared 24mm MDF with damped sandwich design the result was amazing. Then you firs realise how much ordinary "thick" even well braced cabinet sound.
Thanks for the link. Interesting, but it's very much unobtainable here. When you tried the damped sandwich you mention, did you make it yourself or was it a commercially available product? If made it yourself, how did you make it?
Thick walls of MDF are unlikely to be an effective way to make a stiff cabinet. MDF is a pretty limp material compared to alternatives like plywood. Thick walls are also not particularly effective because they add mass which pulls down the resonant frequencies and much of the material in the middle doesn't do much to resist bending.
Girders usually have an I shaped cross section in order to get most of the material on the outside to resist bending. The panel equivalent of that is something like the pro-core picture shown a few posts earlier. Bracing is likely to be the most effective way to get the stiffness up. This doesn't need to add much mass if it is added to eliminate what would have been the antinodes of the lowest modes. However the bracing must stiffen in all directions if the whole structure is to be stiffened.
Indeed. Damping is only useful for resonances and if you can avoid them then you need minimal damping.
Lowering resonances is fully worthwhile. Harwood found that resonances were less audible if they could be pushed below the midrange. Although some think that extra stiffness will put resonances out of range, inpractice the very stiffest caninets only succeed in pUshing resonances into a worse range.
And how do you avoid them?
All structures have multiple and complex modes of resonance. Even with Herculean efforts it is hard to push them more than an Octave from their starting point.
Damping is the answer. Have sufficient damping and the frequency of resonance doesn't matter. Add mass in the form of damping material and don't chase after extraordinary stiffness.
David
I think you may have lost the thread somewhat. LewinskiH01 is building separate cabinets for his drivers and we are discussing what to do with the subwoofer cabinet (<80Hz) and possibly the midbass cabinet (80-450Hz). Damping to be used for the cabinet/s that need it.
Agree with David. Lossy materials are good. As in, limp materials. For the subwoofer cabinet you want first and foremost mass to counter the reaction forces of the accelerating cone. And the material should ring as little as possible. Since MDF is lossy and heavy, very good and economical to use that.
Let´s throw another intuitive analogy in the group. Suppose you want to make a guitar body. Then think about the worst material you can imagine. That would be the best for a speaker enclosure, whatever frequency range you want to feed into it. My list from worst to best (for the guitar body) would be loose sand, rubber, weak PVC, MDF, multiplex, fir wood. Since rubber, sand and weak PVC lack structural strength, you wind up with MDF for speakers.
A laminate would be even better. Imagine a guitar built out of triplex with soft rubber as its middle layer. Would only make sound if smashed hard against something else.
Let´s throw another intuitive analogy in the group. Suppose you want to make a guitar body. Then think about the worst material you can imagine. That would be the best for a speaker enclosure, whatever frequency range you want to feed into it. My list from worst to best (for the guitar body) would be loose sand, rubber, weak PVC, MDF, multiplex, fir wood. Since rubber, sand and weak PVC lack structural strength, you wind up with MDF for speakers.
A laminate would be even better. Imagine a guitar built out of triplex with soft rubber as its middle layer. Would only make sound if smashed hard against something else.
I see. Yes subs are the one case (and possibly small mid cabinets) where you can push the resonances above the range of operation.
Hi Alexander,
This method is the way I usually build: MDF+ plywood sandwich. Using hardwood (oak dowels) for cross bracing. The only way to improve the sandwich is to slip a sheet of 30# roofing felt in between the 2 layers. It's a very long, complicated and tedious process, but results in a superior enclosure
especially for a DIY attempt.
Here is an interesting link:[url]http://www.dagogo.com/a-whitepaper-the-audibility-of-cabinet-panel-resonanc [/URL]
I have a thread going on this topic as well, however focused on driver de-coupling. I was wondering what the effect of an actual semi-liquid, aka, Acousti-seal would have as the constrained layer as opposed to the solid viscous-elastic. This is a construction material used as a sealant between mating surfaces whose benefit is a permanently soft, non-hardening consistency which helps to minimize gaps due to warpage over time of the structure it's applied to, ie: double studs, bottom/top wall plates in house framing. It seems this would be a superior dampening material, no? What are you guys' thoughts on this?
http://www.dagogo.com/a-whitepaper-the-audibility-of-cabinet-panel-resonanc
I have a thread going on this topic as well, however focused on driver de-coupling. I was wondering what the effect of an actual semi-liquid, aka, Acousti-seal would have as the constrained layer as opposed to the solid viscous-elastic. This is a construction material used as a sealant between mating surfaces whose benefit is a permanently soft, non-hardening consistency which helps to minimize gaps due to warpage over time of the structure it's applied to, ie: double studs, bottom/top wall plates in house framing. It seems this would be a superior dampening material, no? What are you guys' thoughts on this?
http://www.dagogo.com/a-whitepaper-the-audibility-of-cabinet-panel-resonanc
Here a link to a paper concerning driver decoupling from Andrew Jones, former Director of Engineering, TAD and designer of the TAD Reference 1. Among the materials used in the study was EAR type E-610-1 isolation grommets.
http://www.linkwitzlab.com/Driver Decoupling.doc
Most acoustic sealants, used to fill in gaps at the ends of panels and walls, are usually more elastic than viscoelastic, and in general not that well damped.
In my thread here:http://www.diyaudio.com/forums/multi-way/277934-isolastic-speaker-design.html , I mention my KEF Series2 which have decoupled bass, mid, and tweeter drivers. Your link seems to confirm KEF's claims. It would be nice to have a Series1 pair that came without decoupling to compare with. Old speakers but still relevant imo.
In regard to the semi-liquid, I would utilize it by constructing a cavity between inner and outer panels. Simply install a 1mm thick (or whatever)strip around the perimeters of the walls, thus containing the Acousti-seal with fasteners located only at the perimeters. What do you think of this idea?
Hi all,
Very interesting thread I would say ;-) ... BTW, any of you ever tried something like these products for damping or sheer mass:
http://www.ecomass.com/products/
Densities up to 11 g/cm3 ... but I don't know how it sounds, though ...
Cheers,
Jesper
Very interesting thread I would say ;-) ... BTW, any of you ever tried something like these products for damping or sheer mass:
http://www.ecomass.com/products/
Densities up to 11 g/cm3 ... but I don't know how it sounds, though ...
Cheers,
Jesper
My subs are already built. They could definitely be improved upon, but right now my focus is on the midbass, midrange, and tweeter sections.
Midbass (80-450Hz) seems the most challlenging from a resonance point of view. A pentagonal cross-section is appealing in that it doesn't have parallel surfaces. A terminated transmission line has other appealing aspects, including the added bracing it implies.
Sandwiching plywood, sound barrier rubber, and MDF seems like an alternative that can combine strength and damping (and puts mass away from the middle, or in other words increases the inertia mommentum). Getting them to bond evenly throughout the surface is what looks most challenging. I don't have a 10 ton press handy!
I need to put more thinking into this.
Thanks all for the input.
well ...
https://search.yahoo.com/yhs/search?p=t-6061+t6+&ei=UTF-8&hspart=mozilla&hsimp=yhs-001
Magico Loudspeakers | Enclosures
The Mighty Magico Q7 | Stereophile.com
something to consider ...
https://search.yahoo.com/yhs/search?p=t-6061+t6+&ei=UTF-8&hspart=mozilla&hsimp=yhs-001
Magico Loudspeakers | Enclosures
The Mighty Magico Q7 | Stereophile.com
something to consider ...
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