insulation sound board are compressed fiberglass or basalt made into curtin wall insulating boards. I doubt if you would get much sound unless you soaked them in resin.
Interesting comment about the plywood. Dayton's primer on exciters say ply is a nono.
Keep in mind I'm in the learn curve stage and just ordered parts but from what I've read high density yields better high end. Hmmm got to order me some ply to test. Thanks...s
Interesting comment about the plywood. Dayton's primer on exciters say ply is a nono.
Keep in mind I'm in the learn curve stage and just ordered parts but from what I've read high density yields better high end. Hmmm got to order me some ply to test. Thanks...s
Elac Imago no longer sold but I found this ebay listing.
ELAC Imago Bildlautsprecher in Schleswig-Holstein - Schwentinental | Lautsprecher & Kopfhorer gebraucht kaufen | eBay Kleinanzeigen
LOL look at it! Go on somebody, buy it and report back!
ELAC Imago Bildlautsprecher in Schleswig-Holstein - Schwentinental | Lautsprecher & Kopfhorer gebraucht kaufen | eBay Kleinanzeigen
LOL look at it! Go on somebody, buy it and report back!
LOL here are some more.
Dirt cheap!
ELAC Catalogue 2002 D GB Brochure Picture-Speaker Brochure Imago Panels Catalog | eBay
EDIT - Forget it that is just for the catalog
Dirt cheap!
ELAC Catalogue 2002 D GB Brochure Picture-Speaker Brochure Imago Panels Catalog | eBay
EDIT - Forget it that is just for the catalog
And even cheaper is to use vacuum storage bags intended for clothing, and your vacuum cleaner.
Hand Laminate & Vacuum Bag a Simple Carbon Fibre Part (inc. Vacuum Cleaner method!) - YouTube
I made carbon/balsa/carbon panels this way that turned out quite good.
Eric
I prepared this table.
R is radiation coefficient which is what you want to maximise.
I left out a lot I was unable to buy locally
wood Youngs modulus density R
Balsa 3.71 150 0.001048456
Bamboo 18 500 0.000379473
Spruce 11.03 425 0.000379057
Basswood 10.07 415 0.000375355
Aus Cedar 9.22 485 0.000284284
Coachwood 15 600 0.000263523
Dillenia 12 575 0.00025124
QLD Maple 10.83 560 0.000248332
Blackwood 14.82 640 0.000237768
BH Sassafras 12.6 620 0.000229931
Silver Maple 7.86 530 0.000229772
Tas Myrtle 12.62 625 0.000227358
African Mahogany 10.6 640 0.000201087
Ash 12.31 680 0.000197863
Silky Oak 7.93 590 0.000196498
Maple 11.8 690 0.000189525
Zebrawood 16.37 805 0.000177146
EDIT: I just added balsa. Streets ahead if you can put up with its fragility
PS. Most of these are tonewoods used in stringed instruments with a few added for comparison
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Ignore most of what you read! As far as efficiency (loudness) plywood is only okay. But for sound quality, it can be quite good.
One problem is that people can use terminology that is vague. When people say "high density yields better high end" what they probably really mean is "hard" rather than "high density".
High density really means "heavy per unit volume". While "hard" means "doesn't compress easily". Often, denser means harder, but not always.
For DML purposes, you really want "hard" but NOT "dense". Hard is needed for high frequencies, and light (i.e. not dense), is needed to be efficient (loud) at all frequencies.
Eric
That is interesting but in that video he is referring to carbon fiber in particular which needs low pressure with that resin.
At this stage he talks about the supermarket vacuum bag.
Hand Laminate & Vacuum Bag a Simple Carbon Fibre Part (inc. Vacuum Cleaner method!) - YouTube
He says the hand pumps get to 80% pressure reduction and vacuum cleaners only 20%.
You would think the hand pumps might lose their pressure but apparently that is not the case.
Custom Phi Guitar - Blog - Rockit Talk Community
https://acousticguitarconstructionforum.com/viewtopic.php?t=1475
The luthiers use high pressure when applying veneer to laminate nomex sheets so high pressure might be more appropriate. I wish I had known that the supermarket bags could be used this way though before ordering the roarockit.
EDIT - When I say high pressure I really mean high suction or low pressure, sorry.
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Good. I agree that's a good starting point. What I'm less sure of is if there is a point where the coincidence frequency becomes too low.
As radiation efficiency increases, coincidence frequency (fc) decreases. And DML panels start beaming high frequencies (at 90 degrees) at the panel's coincidence frequency.
So the challenge may be to find a material/construction that gives the best balance of high E/pho^3 (or B/d^3) for good radiaton efficiency, but low enough E/rho (or B/d), to avoid objection-able high angle beaming.
But I don't know how low you can push fc and before the edge beaming is audibly noticeable.
Eric
But you'd feel much worse if you bought a true composites vacuum pump and all the acce$$ories!
You can also use a "Foodsaver" vacuum sealer for this kind of work. But the clothing storage vacuum bags are really convenient because you don't have to create new a heat seal every time. Plus, the size of the clothing bags is better suited to DML panels. Foodsaver bags are too narrow.
A vacuum cleaner will generate about 6 psi of vacuum. It doesn't seem like much but it's actually plenty for most work. I rigged a method with a suction cup to use the Foodsaver vacuum pump with the clothing bags to get up to about 22 psi vacuum. A hand pump I tried (pump n seal) will get much more vacuum, but I don't think there's much benefit.
Eric
Hi Steve,
Is EPS sheet is same as thermocol sheets as shown in the attached pictures. These thermocol sheets are very light in weight and very fragile, and thickness of around 1cm.
If we need to experiment by putting exciters on different panels or different position on same panel , how to attach and remove without effecting the exciter and the panel material.
Attachments
![IMG-20210913-WA0000[1].jpg](/community/data/attachments/907/907632-51097f55476cd6d47b433e3cfb6a499e.jpg)
![IMG-20210913-WA0001[1].jpg](/community/data/attachments/907/907635-44bb35abd263c47a7fce3f8834dc713c.jpg)
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Aeon patent
I have put the German paper through a different translator which is much better and makes the patent understandable.
Some points:
1) Figure 9 is indeed from the Elac Imago. Has anyone ever heard these?
2) He uses 1.5mm end-grain balsa as a core for the reasons outlined in [00051]
3) The pore filler is only there to stop resin from seeping into the balsa and destroying some of its properties. Any light and thin layer would do eg. thinned PU
4) The panel appears to not be supported at the back and is free-hanging somehow. So no supports on the exciters.
5) The so-called "acoustic lens" is still very confusing. These are typically used in front of two drivers to prevent combing of the frequency response due to destructive interference. However in this design, for the life of me it seems to be on the back. And I am not even sure which part is the acoustic lens. Is it fig 6? Or is it fig 8b? And what do 8c and 8d do? Why is it on the back which is absorbed anyway? Or is it on the front?
Originally I thought it was confusing because of the translation. This latest translation is good enough to understand but it is not clear at all what the inventor was referring to. Now I just think it is a bad patent.
I have put the German paper through a different translator which is much better and makes the patent understandable.
Some points:
1) Figure 9 is indeed from the Elac Imago. Has anyone ever heard these?
2) He uses 1.5mm end-grain balsa as a core for the reasons outlined in [00051]
- a) Lightweight core and thus a high efficiency of the bending wave transducer.
- b) Due to the very high compressive and tensile strength in the exciter's direction of excitation, even the smallest energies in the high-frequency range are not swallowed by the core material.
- c) The inhomogeneity of the lightweight wood counteracts pronounced resonances.
- d) Due to the damping properties in the direction of propagation of the bending wave, the positive and negative amplitudes of the bending wave from the excitation point in the direction of the edge of the panel according to the invention become smaller and smaller.
- This results in a more rapid decay of the panel, pronounced resonances are reduced and a bending wave transducer with the panel according to the invention still operates to a certain extent as a bending wave transducer even below the coincidence frequency. The reason for the fact that the panel still works to a certain extent as a bending wave transducer below the coincidence frequency is seen in the fact that the negative and positive amplitudes become smaller and smaller from the excitation location towards the edge and thus below the coincidence frequency there is no complete cancellation (acoustic short circuit) of the amplitudes.
3) The pore filler is only there to stop resin from seeping into the balsa and destroying some of its properties. Any light and thin layer would do eg. thinned PU
4) The panel appears to not be supported at the back and is free-hanging somehow. So no supports on the exciters.
5) The so-called "acoustic lens" is still very confusing. These are typically used in front of two drivers to prevent combing of the frequency response due to destructive interference. However in this design, for the life of me it seems to be on the back. And I am not even sure which part is the acoustic lens. Is it fig 6? Or is it fig 8b? And what do 8c and 8d do? Why is it on the back which is absorbed anyway? Or is it on the front?
Originally I thought it was confusing because of the translation. This latest translation is good enough to understand but it is not clear at all what the inventor was referring to. Now I just think it is a bad patent.
Tsardoz.
Thanks for the patent update.
On this site I have made many recordings of different materials for dml panels.
My point about panel damping is that it will usually alter the sound and not necessarily in a good way.
It may give you a flatter frequency response but at what cost ?
I usually use other methods which I have described on this site , to sort out these problems.
I usually try to increase the panel performance in a good way , and not to reduce it.
My panels are always free floating with the odd exceptions.
Steve.
Thanks for the patent update.
On this site I have made many recordings of different materials for dml panels.
My point about panel damping is that it will usually alter the sound and not necessarily in a good way.
It may give you a flatter frequency response but at what cost ?
I usually use other methods which I have described on this site , to sort out these problems.
I usually try to increase the panel performance in a good way , and not to reduce it.
My panels are always free floating with the odd exceptions.
Steve.
Paulownia or Kingswood as it some times is called could be a good candidate. Light weight and relatively strong/stiff/hard
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OK I have made up a spreadsheet using values from the attached paper.
(download here
Loading Google Sheets)
Using values from the paper I get the following
panel fundamental resonance 256.47 f0 Hz
coincidence frequency 10479.51 fc Hz
which is close enough to the original numbers. Now check the comment paper which says:
Interestingly, at frequencies well below the critical frequency (10 214 Hz for the experimental DML), the far field so generated is omni-directional and the associated sound power per unit mean square force is independent of frequency and plate stiffness and inversely dependent on the square of the panel mass per unit area. The contribution of this source of sound, relative to that of the reverberant vibration field in the plate, increases with the plate loss factor.
Control of the panel mechanical loss factor is vital, because the proportion of input power radiated by the reverberant component of panel vibration is crucially dependent upon the ratio of mechanical to radiation loss factor.
What this is saying is that since fc>>f0 the panel is acting not so much as a flexural resonator but as a panel piston speaker. In this case SPL is independent of frequency and depends ONLY on the panel mass per unit area which should be as low as possible for high SPL (desirable since the exciters are low power).
Now check the German patent design...
Young's Modulus (Gpa) thickness (mm) density (kg/m^3) volume fraction Material Notes
Layer 1 80 0.5 1500 0.2 carbon fibre
Layer 2 3.71 1.5 150 0.6 end balsa
Layer 3 80 0.5 1500 0.2 carbon fibre
composite 6.00 2.5 690
Poisson ratio 0.1 leave at 0.2 if not known
stiffness per unit width 7.89 D Nm/kg^3
density pu area 1.725 mu
D/mu 4.57
Panel Length (mm) 255
Panel width (mm) 185
Area (m^3) 0.047
panel fundamental resonance 142.38 f0 Hz
coincidence frequency 8963.02 fc Hz
Again it is behaving as a piston speaker but even more so ... recall
Control of the panel mechanical loss factor is vital, because the proportion of input power radiated by the reverberant component of panel vibration is crucially dependent upon the ratio of mechanical to radiation loss factor.
We do not know what the mechanical loss factor is but the inventor went to great lengths to make it quite high (balsa damping, lossy coupling to frame, incisions around edges, weights) so this is acting even more as a piston speaker.
Feel free to download the spreadsheet and play with it. It turns out the design I was proposing is really bad for bass extension as it is just too light and stiff. There must be a happy medium.
EDIT: Note the f0 is about what the inventor was getting so I think this approach looks reasonable
"The ideal material for mounting an exciter is a thin, lightweight sheet of material with high compressive strength and moderate to high bending strength. The compressive strength of the material has the greatest effect on the treble extension of the resulting ‘speaker’ (affecting ‘detail’ and ‘air’), while the bending strength of the material influences the midrange and low frequency efficiency of the ‘speaker’." From From Dayton website
Refering to the German patent recently discussed:
The back panel (fig.6) which is mentioned with several holes and was mentioned to be some sort of acoustic lens, sparked my curiosity. And after some searching on the web I found this loudspeaker: Ondacustica ultra high-end loudspeakers | Products which also seem to use some sort of bending wave principle together with a back panel at the with holes in it.
What effect would this have on our DML speakers we are discussing in this thread? Could it disperse the sound from the back of the panel and make the panel work as if it further from the back wall then it actually is?
The back panel (fig.6) which is mentioned with several holes and was mentioned to be some sort of acoustic lens, sparked my curiosity. And after some searching on the web I found this loudspeaker: Ondacustica ultra high-end loudspeakers | Products which also seem to use some sort of bending wave principle together with a back panel at the with holes in it.
What effect would this have on our DML speakers we are discussing in this thread? Could it disperse the sound from the back of the panel and make the panel work as if it further from the back wall then it actually is?