Yes.
Yes. A general equivanence commonly used for stiffness between typical quality multi-ply and average MDF is 18mm ply = 1.25" MDF (both these materials have a fairly wide deviance from the average)
dave
Attachments
Consider this:
Points already covered:
1/ The distribution of frequencies in music drops above a certain threshold
2/ HF is easier to damp
and
Intensity/power is inversly proportional to the square of the frequency.
Take all those and you see that the power available to excite a resonance falls with the forth power of frequency.
dave
Points already covered:
1/ The distribution of frequencies in music drops above a certain threshold
2/ HF is easier to damp
and
Intensity/power is inversly proportional to the square of the frequency.
Take all those and you see that the power available to excite a resonance falls with the forth power of frequency.
dave
Planet10 , The funken enclosure you pictured above seems to have front ( baffle ) to back bracing on the left portion of the picture , My design calls for side to side brace as i understood is better from the AES picture you linked in page 3 .
Are you sure that is OK ?
Should I brace front to back more instead of a single round brace
Or is it all not such a big issue as long as I brace heavily ,
Use 18mm MDF + 18mm birch + 18mm MDF on a single wall ? isn't that a bit overkill
Are you sure that is OK ?
Should I brace front to back more instead of a single round brace
Or is it all not such a big issue as long as I brace heavily ,
Use 18mm MDF + 18mm birch + 18mm MDF on a single wall ? isn't that a bit overkill
sorry for my bad english: all other parameters being equal, the power propagated by the wave is proportional to the frequency; thus you need to give more energy to whatever a high fr resonating structure to make it resonate. Not to be confused with damping, which is the opposite (damping high frs is easier)
That makes sense to me that the vibration of the cabinet walls would contribute to the far-field sound in a non-linear way. However, I don't think that invalidates the study nor the usefulness of doing the measurement.
For example, if adding a fill of 50% fiberglass results in a suppression of 20 dB of vibration across a large region of the spectrum, then it can be reasonably assumed that wherever the resonant problem persists (if in that region of the spectrum) it would be reduced by about 20 dB in the far-field.
That still is an improvement over the initial condition regardless of what the far-field readings told you.
In that regard measurement of vibration is still a valuable tool for determining the effect of box stuffing and internal bracing. Additionally, it is a far easier method for the home builder to use than attempting far-field measurements with a microphone in an environment where walls, ceilings, and floors complicate microphone sampled measurements. When you consider it is nearly impossible to get reliable far-field measurements down into the bass region, measuring wall vibration is a gift.
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I've been pondering this thread for the last three hours, and my only conclusion is that the good Doctor is a master of understatement.
A few terms that seem to be missing from the discussion are 'inertia', 'internal friction', and 'triangles'.
Taking the last first, I think the "cross(ed) braces" discussed would benefit from 4 more diagonal braces that bisect the squares formed, creating triangles. Earl's comment about bridges was on point, but perhaps he should have specified "truss" bridges.
Internal friction is the essence of damping. It's also the key to why wood is used in so many musical instruments. Good luthiers use solid pine for the tops of their guitars partly because it resonates well, but mostly because it absorbs those nasty overtones you hear from lesser instruments made of plywood. Everywhere I go on the 'net, the anecdotal evidence from both hifi buffs and guitar players keeps insisting that "MDF sucks tone". I suspect the truth may be just the opposite - MFD doesn't damp the frequencies the ear considers "harsh", but clearly, woods products with continuous grain sound better. Since it's unlikely that you'll remove all resonances from your cabinets, it makes sense to me to use a material that will at least provide musical resonances.
Finally, the law of inertia suggests that with enough MDF, the above point may be moot (or mute!). There has been a lot of discussion about exciting resonances, but it all seems to be assuming that the process is linear. It's non-linear on two axes - amplitude and frequency. The brute force answer is mass.
There seems to be a minority consensus that raising the resonance of a panel is a "good thing". I say it's a good thing if you move the resonance into a frequency band that will be damped by the materials and construction used. In Art Ludwig's graph ( http://www.silcom.com/~aludwig/images/panelvibes.gif ) it seems to be occurring with the roofing felt (green), not so much with the vinyl (magenta). (BTW, those peaks at 2K and above are the response of the pickup used. Guitar pickups are like that.)
Here's hoping this exercise has cured my insomnia, I'm off for a nap!
If you cannot correlate the vibration with a "problem" at the ears, then its all moot. You are just playing a numbers game.
Here's hoping this exercise has cured my insomnia, I'm off for a nap!
Hope you had a good nap! Correcting all the misinformation about audio never seems to relaxe me, but alas, you might be different!
Its not always about "Just" the ears
If some people deem it valuable to know the resonance of a box even if we can not hear it then so be it. I never understand how that can be mis-represented or a moot point to them. Sure its a moot point to some people but no one if forcing anyone else to do anything. Its all just discussion and there are many goals and many different objectives in any hobby.I do 100% agree that people go overboard on the whole barcing/dampening discussion and your post earlier was great.
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That's okay.
You stated earlier that, "To my way of thinking bracing creates more problems than it solves."
You stated that was your theory. Surely you have some basis for that theory and that is what I am trying to understand; what makes that theory tick.
hehe, why back up theory when opinion is generally all that is needed
Ha!
Well Glory be! You're the first person I've seen mention that. (OK, I might have missed another somewhere).
The point is that it does not need to be an absolute number. A relative number is fine.
If you reduce the vibration at a resonant peak by 20 dB it is probably going to reduce what is heard at the ears by about 20 dB.
Sure, you can run a full frequency sweep with a mic to confirm it and you would expect to do that anyway. However, if you can uses a transducer like an accelerometer as a tool to measure box contribution changes it is both simpler and easier for the home builder. I think it is a good surgical tool to isolate and pick apart the the problems heard at the ear, which when measured in the far-field is an aggregate of a multitude of effects and not just box panel resonances.
I really don't know your preferred approach, OFAT (On Factor At a Time) or DOE (Design of Experiments), but if you use DOE you are in a realm well beyond most builders here.
Ha!
Well Glory be! You're the first person I've seen mention that. (OK, I might have missed another somewhere).
That point has been stated, err..., I mean, ignored several times before.
Quote used as restatement..
AGAIN:
Panel Damping, (and damping in general), should be the main emphasis. *NOT* bracing.
The bracing discussed here does very little to alter the rigidity of the panels and shift its resonant behavior higher in freq.. The panel's resonant behavior is largely "set" by it's shape and material.
Even then, *where* you brace the panel *far* better determines your over-all effectiveness then *how* you brace the panel (..at least with regard to what has been discussed in this thread).
Talk of "T" or "+" shapes for bracing is absurd. Again, we aren't concerned with transferring any significant loads/stress - it isn't a load-bearing structural issue.
Targeting areas on the panel that are more likely to deform is a MUCH better use of bracing. Moreover, those areas are NOT areas that are likely to be equidistant from other panels.
This means that "T" or "+" shapes of bracing are likely to provide *LESS* of an improvement, because doing this almost always ends up with bracing contact points that are not located in the right spot to properly effect the panel. (..the "middle" of a rectangular panel is almost NEVER the correct location.)
Additionally, utilizing more surface are for the brace's contact point, like a "[+]" shape, often *REDUCES* overall effectiveness (..with poorer connection and poorer rigidity). (..on the other hand it also marginally increases damping, but not enough to really be effective.)
If you are really interested in increasing rigidity then select different materials, decrease panel size, or increase panel thickness.
With the material selection consider its rigidity with respect to direction.
MDF is basically "directionless" on the basis of material alone (..NOT shape). Plywood on the other hand is much stronger on its lamination edges then on its panel sides - in other words a "trans-lam" build like the Magico Mini will most certainly increase rigidity. Also the Mini's "cross-bracing" is NOT like the bracing discussed in this thread. Because it's a "trans-lam" design, the bracing is actually part of the panel. There effectively is no "connection point".
As far as panel size is concerned, you probably can't do much with it. (..you probably can however alter shape to some extent.)
Increasing panel thickness is a "double-edged sword". Increasing thickness can substantially shift resonances higher in freq.. On the other hand, the thicker the material is, the more difficult it is to damp (..and it's also more prone to sending vibration to adjoining panels).
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ScottG it appears that what you described cannot be done with normal means and basically all conventional DIY ways are "wrong" .
I really cant use the birch the way the magico mini's are built "trans-lam" as you call it because it wastes alot of material .
I cannot decrease panel size.
Panel thickness will be 25 mm birch and I think going any thicker is a waste.
So how would you brace it ?
many different opinions in here ...
I really cant use the birch the way the magico mini's are built "trans-lam" as you call it because it wastes alot of material .
I cannot decrease panel size.
Panel thickness will be 25 mm birch and I think going any thicker is a waste.
So how would you brace it ?
many different opinions in here ...
I would think that increasing panel thickness (and therefore mass) would make a panel less prone to resonating, and if there's less resonances to damp, then to the contrary a thicker panel would be easier to damp.
And to continue the theme, if a thicker/higher mass panel is more resistant to resonating, then it doesn't seem like it would be logical to conclude that a thicker panel is more prone to sending vibrations to adjoining panels.
ScottG it appears that what you described cannot be done with normal means and basically all conventional DIY ways are "wrong" .
I really cant use the birch the way the magico mini's are built "trans-lam" as you call it because it wastes alot of material .
I cannot decrease panel size.
Panel thickness will be 25 mm birch and I think going any thicker is a waste.
So how would you brace it ?
many different opinions in here ...
They aren't necessarily wrong, just not terribly effective and often even less effective. There are however OTHER issues that might make them more "wrong".
Actually the Mini's "bracing" is almost redundant (particularly if you increase panel thickness). This means that a birch plywood "trans-lam" is still an excellent way to increase rigidity.. and just skip the notion of bracing at all. IF you do that then you aren't really wasting material (beyond the cutting process), AND you can determine the wall thickness to your desire. Plus, (because it's a lamination), vibrations along the length/width of the lamination panel are more "discontinuous" and damped as a result (..the glue you will be using in particular will present a "loss").
The only real down-side is increased planning and a hell of a lot of cutting (..but most pieces should be fairly uniform so even the cutting shouldn't be to bad).
35 mm thickness for a good plywood "trans-lam" and an enclosure similar in size to the one you are proposing should do the trick - rendering it largely "inert". Even the dimensions shouldn't change that much considering that you can *reduce* volume because of the absence of cross-bracing displacing interior volume.
You can also "stagger" the pieces in the "lam" at the corners, rather like a box-cut joinery joint.
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Increasing thickness may well result in greater damping of resonances (depends on the materials loss), and it may even do so for the *net* result when compared to a thinner but better damped panel. It is however *easier* to damp a thinner panel than a thicker one.
Again, you may be correct about the *net* result. I think it's largely about *how* panels are joined, and the character of the material used (in the shape it's used).
Thats not really true, which is my point. If it is inaudible now then lowering it 20 dB does not make it MORE inaudible - there are not degrees of inaudibility. The SPL contribution to the total MAY drop by 20 dB, but thats different than what is "heard". We all like to think that "if its there, I can hear it", but thats simply not true. Masking is a major effect in our hearing and once something is masked its gone.
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