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A Study of DML's as a Full Range Speaker
A Study of DML's as a Full Range Speaker
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Old 27th October 2021, 02:41 PM   #3981
aagas is offline aagas
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vdijev --

From a purely empirical perspective and new thoughts on things I've posted prior...

Experiment 1
I've had (if subjectively) great success with large (approx. 28" wide X 72" high) aluminum honeycomb core covered with aluminum skin panels. A single (Dayton Audio Thruster) exciter on each can drive them louder than I can stand.

Note: these panels have a modest aluminum edging covered by the the skins.

I could continue to tweak these DMLs, but they sound so good as I have them, I just don't get around to it.

Note, these panels have nothing resembling "dampening".
Speculation & reverie ...
I originally conjectured that the key to the performance of, the above described, panels rested in some function of size vs weight vs rigidity.

I've begun reconsidering rigidity or perhaps expanding my notion of it. More specifically, I think the compressive strength (across its narrowest dimension) better maps to what I had earlier thought about "rigidity"

XPS panels painted with PVA or epoxy have a lot of this kind of compressive strength. Carbon fiber, spruce, and various plywoods do too. While very thin, I think a canvas panel treated with PVA also does, it really creates a stress skin panel/membrane.

This said, I don't think this kind of compressive strength accounts for everything.

It may seem like a contradiction, but I now believe effective/successful panels need to flex/wobble (and maybe a lot).
Experiment 2
My next DML build used 1/16" thick plexiglass. Plexiglass has high compressive strength (almost to the point of brittleness), but it (at least the 1/16th inch plexiglass) wobbles like crazy, "especially" in its long dimension.

These panels measure approximately 18" wide X 32 1/2" high.

I still have work to do on them, but they sound pretty darn good.

Again, these panels have no dampening and no frame (I hang them with fishing line).
Next
I plan to pick up some aluminum flashing. Essentially, aluminum, as thin as possible, while remaining a sheet rather than foil.

I remain unclear why Steve (spedge) thinks a bass drum head wouldn't work. Maybe too piston like rather than wobbly? ;-)
Quote:
The creation of something new is not accomplished by the intellect but by the play instinct.

—Carl Jung
Updates to follow.

-- Andreas
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Old 27th October 2021, 04:57 PM   #3982
xrk971 is online now xrk971  United States
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A Study of DML's as a Full Range Speaker
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A couple of M######rs used an array of exciters arround the whole perimeter of a plate to cancel the reflections, and kind of achieved an infinite plate repsonse.
Very interesting concept. Is there a link to this?
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Old 27th October 2021, 08:19 PM   #3983
vdljev is offline vdljev  Argentina
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XRK the papper is called: "A simulation study on the array control of a rectangular panel speaker for improving the sound radiation performance". Its no in researchgate, i'm not sure how i got it... so i made a drive link to the papper collection: DML - Google Drive
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Old 27th October 2021, 08:37 PM   #3984
vdljev is offline vdljev  Argentina
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Interesting findings aagas, honeycomb is really expensive here but not an option... was thinking about making my own using the carborad honeycomb fill for hollow doors, wich is cheap as lead. I should find a way to glue the faces tho... maybe a slow drying agent, it will take me about 20 min to put glue in all the honeycomb...
About your speculation, you are right according to Kirchoff-love theory and the refined models for bending waves, the math is quite clear in the Kuonan Li thesis. In that link there is an excell that applies the math to find f0 and fc, wich may be flawed tho, i should speak with some acoustic teachers to be sure... But yes what matters the most is the bending stiffness (young modulus * Inertia momment) over mass (expressed as linear or area depending on the expression used). So yes, the main concerns about materialss are density and Young modulus. Inertia momment for a plate is fixed (for same thickness) and depends on poisson ratio, but i dont think there is too much variation AKA poisson ratio influences less. As stated before, ratio B/m should be kept low, as a high mass would create little efficiency, the choice is a low B, but not too low, cant remember why, its in Kuonan Li. For the honeycomb, its a high anisotropy material (propierties differ depending on the direction considered) so take into account the aspect ratio conslucions of Zeker.
Elastic-Viscoelastic Frames seem essential to me, there is some real cheap pitch material wich is used to fill concrete expansion joints (quite flammable prob). They really reduce the amount of FIR or IIR used after in low freq.
Hail Jung forever young to!
But, its always important to have an objective measurment to contrast with (not the other way arround as its usually made by researchers). It helps you understand why some things happens. For example i listen to alots of new details if the Freq response is quite hi end oriented, but the overall response may be awfull... If you made it the other way arround you would prob say, in that case, this will sound like sh·t and you wouldnt realize the "pros" of listening with another parciality, lets face it, partiality is always there when you diy, each time i turn my speakers i`m like a child in christmass opening a gift, expectetion and satisfaction is too high, cant help it
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Last edited by vdljev; 27th October 2021 at 08:44 PM.
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Old 27th October 2021, 09:30 PM   #3985
xrk971 is online now xrk971  United States
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A Study of DML's as a Full Range Speaker
Quote:
Originally Posted by vdljev View Post
XRK the papper is called: "A simulation study on the array control of a rectangular panel speaker for improving the sound radiation performance". Its no in researchgate, i'm not sure how i got it... so i made a drive link to the papper collection: DML - Google Drive
That’s a nice library of papers on DML’s!

I hope you keep it around - I’ll put a link to it from Post 1 so it won’t get lost.

Thanks!
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Old 27th October 2021, 10:44 PM   #3986
spedge is offline spedge  United Kingdom
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quote
It would be interesting to see what happens if you do do tests on drums , so don't let me put you off.
It would all be useful information.

hi Andreas.
i did not say a drum head would not work .
it will work to some extent ,but how well it will sound i don't know ?
its a bit of a balancing act with the tension, if you are trying to run the drum panel full range.
the art panel and my hoop are very similar to a drum head , but not as tight.
steve.
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Old 28th October 2021, 12:39 AM   #3987
vdljev is offline vdljev  Argentina
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U.U. Thank you XRK for all your wurk here , some day i ll make some XPS cabinets . I have more in the wave field synthesis folder, will check again if the arent some DML around there, im sure they are, and add them.
Also will make it editable for anyone with the link so anyone can add papers or things
Regaards ! <3
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Old 28th October 2021, 09:19 AM   #3988
Mehtasab is offline Mehtasab
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The tracks were recorded on an iPhone and then converted to audio MP4 to allow me to upload to the site.
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Old 30th October 2021, 12:35 PM   #3989
spedge is offline spedge  United Kingdom
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Mehtasab.
I presume you are having problems uploading recordings ?
Steve.
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Old 1st November 2021, 12:16 AM   #3990
Veleric is offline Veleric  United States
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Quote:
Originally Posted by xrk971 View Post
That’s a nice library of papers on DML’s!

I hope you keep it around - I’ll put a link to it from Post 1 so it won’t get lost.

Thanks!
Yes, thank you for this collection vdljev!
Many I have read but not all. In particular, IIRC, I have tried finding the Panzer Harris paper before without and luck. Thanks!
Eric
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