constrained layer damping with MDF and Ply

I learnt that aluminium and other materials don’t even have a formal yield point like steel has (picture), but that we agreed on an arbitrary value that keeps things together long enough.
yes that is true. There is an accepted definition of yield point that we use for aluminum and titanium alloys which I believe is 0.2% plastic strain. Within the realm of fracture mechanics, we model the stress-strain hysteresis behavior of the crack tip, so the exact numeric value of the yield point is not so important.
 
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Oh yes I get your point. If you go to thin, the constrained layer stiffness kicks in and you're back to a plank of wood. So it's a balancing act.

That's the issue :s

Yes but too thick and the layer won't get out of its elastic region (not enough shear) and will not dissipate any energy. Then it's only mass loading, it will only lower the resonant frequency of the panel.
I did a quick mockup of a CLD in F360. All values are arbitrary. View attachment 1173534 Then with deformation:
View attachment 1173535
View attachment 1173536
I don't know how shear is measured so bear with me. On the 5mm example, the disformation of the damping layer is about 15% (from 5mm to 5.7mm). On the 1mm example we get a ridiculous 125%.
This is a vastly exaggerated example and I don't think a real panel movement will be more than +/-100µm without damping. Meaning, do you even get out of the elastic region with a real 5mm thick layer?
Taken a look in this doc: it shows for geven cld material the effects of variing thicknesses.
Basically one would prefer a plastic material, so the elastic "part" minimal if any.
 

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It's all about acoustic resonance (frequency) and energy.
With more mass, more energy is needed to get something to move (accelerate).
That being said, with a very un-dampened system, this will eventually also resonate, as long as you hit the right frequency for long enough. An additional problem can be at the higher order harmonics of this system.

Another strategy is to push this frequency entirely out of the frequency band, this can be done with stiffness.

What works "best" REALLY depends on context.
Although in general I like to push the resonance frequency as high as possible.
With adequate internal absorption it is possible to dampen those frequencies enough to not be able to hit those frequencies much anymore.

On top of that, there are internal resonances in the material itself, those are called coincidence frequencies.
Typically those are just dampened by adding (a bit of) mass.
I don't think those are that big of a deal for MDF or Plywood, it's a bit of a different story for metal or glass etc.

But yeah, this is one of the many big compromises of a fullrange two-way system.
Because you can't put the resonance frequency to low (works well for pure mids) and to high either (works well for woofers)

Btw, although not related to side wall resonances, the stiffness of a cabinet also has effect on the Qt of the cabinet (+ speaker). Or rather adding a bit of loss in the piston range performance.
Depending on the situation, but in some cases this can be definitely be audible!
And often mistaken for lack of panel resonances btw!!

Also, there is the issue of direct coupling of energy from speaker basket/frame to the cabinet itself as well as the reaction force from the woofer on the cabinet.

VERY often people mistake those for side wall resonances.
Problem is that as soon as you add mass to the panels, this will also change.
Therefor not comparing apples with apples anymore aka BS measurements and conclusions.
My approach so far when building subwoofers has been to raise the resonance frequency outside their band (<80Hz), and build with double layer of 18mm MDF or triple layer of 15mm MDF glued with Titebond, good bracing, no vibration absorption other than fiberglass and polyfill inside the sealed box (about 50x50x50cm). This thread has me thinking that maybe I should add mass to dampen (like self adhesive bitumen or several layers of bitumen paint applied inside) or maybe try CLD. CLD will definitely be tried in my next midbass box (where the resonance is likely closer to the drivers band) but was wondering what your experience has been with subwoofer boxes.
 
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As a rule of thumb:
Use stiff enclosures for (sub)woofers
Use well damped and small enclosures for midrange, plus driver decoupling.
Panel resonances in speaker enclosures typically occur from about 400Hz up to several kHz.
Furthermore, we should not exaggerate the panel resonance issue. In most living rooms other resonating items cause more trouble.
 
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@markbakk
I would like to add that no dampening (insulation) material is needed for subwoofers.
In fact, it adds (a bit of) non-linearity (there is an article about this on Linkwitz's website).
It also doesn't add much, expect for maybe a little bit of extra volume.

Goes to show why a well made FAST system isn't to weird of an idea :)
Even more so in an active system.
 
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Or most measurements are on the rear panel being isolated
from constrained layer. So it looks amazing woo hoo.

Otherwise top isolated layer is just floating and performs worse.
vibrating away.

just so well established that double layer baffle then bracing
basically solves any actual real world issue.
and the MDF vs Plywood gets so old its pointless to hear or read it
again.
 
Basically was pretty cool idea I had long ago.
Many others too.
Looking at thin elastic layer.
Tried thin rubber, thick rubber.
Thin rubber with wool layer. AKA carpet mats.
Maybe elastic layers used as old underlayment
for hardwood floors. And numerous Goops.

Seen thin rubber, then cork
Rubber, then Ceramic.

Done floating ceilings, floating walls etc
etc. Floating ceilings work though because the floater
actually moves and vibrates on the elastic layer.
This keeps bass and low frequency noise
isolated from basement living spaces.

Its all fun, I found it fascinating.
just thick baffles and bracing sounded same.
either way speaker is what it is.

more about driver quality and baffle size for open baffle.
might as well just mount to wall, leave other side open.