OK, I wandered in here by mistake and now I will hasten out. But "encouraging resonances" sounds like a really wrong-headed concept to a conventionally-minded speaker builder.
And if in repeated asking, nobody has been able or seen fit to post an answer to the question of weight or weight compared to films, it is hard to think this thread is achieving adequate technical depth.
Ben
What is the usefulness of that statement about "adequate technical depth"? I hesitated responding to your initial question about weight because it struck me as entitled. Look it up if you want to see how much a panel like this weighs. Google would give you the answer quicker than I would. After leaving it sit for a few days I got over that and decided I'd try to help you out, even though ESL is totally, way off topic.
I don't know much about loudspeaker design but you're probably right that exciting modes is precisely the wrong way to approach a conventional speaker design. Look up some details on DML and maybe check your attitude and have some sympathy and flexibility around what other people might or might not want to get out of a thread like this before pontificating on what's "adequate".
I don't know much about loudspeaker design but you're probably right that exciting modes is precisely the wrong way to approach a conventional speaker design. Look up some details on DML and maybe check your attitude and have some sympathy and flexibility around what other people might or might not want to get out of a thread like this before pontificating on what's "adequate".
A sq foot piece, a half-inch thick might be in the vicinity of 50 gr. Comparable to the cone part of a domestic driver although vastly stiffer (but stiffness per se in a cone does not necessarily lead to great sound). Of course today, so many drivers are made for cars and megawatt power handling, the moving weight can be anywhere even a pound.
B.
B.
Yes thats how it works. It is obvious that your technical depth doesn't reach far enough.
Goebel High End
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Rather than preceding through a list of unavailable materials chosen for ideal properties - yet unobtainable - why not experiment with things you can purchase?
So what if the result isn't ready for a mass market? Once you've made something yourself, no one can deny your achievement.
Rough panels for archtop guitars would be my choice, for a trial run...
http://www.stewmac.com/Materials_an...nd_Wood/Archtop_Guitar_Wood/Archtop_Tops.html
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So what if the result isn't ready for a mass market? Once you've made something yourself, no one can deny your achievement.
Rough panels for archtop guitars would be my choice, for a trial run...
http://www.stewmac.com/Materials_an...nd_Wood/Archtop_Guitar_Wood/Archtop_Tops.html
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Thanks to Altie for this thread. It seems that we all lead busy live these days, and I appreciate the time you spent in constructing your panel and reporting it to this forum.
I have been intrigued by DML panels for some time and am considering a bi-amplified version with a large flat panel crossed over to a conventional sealed-box bass driver. In your research have you come across any rules of thumb for flat panel size and low frequency extension? It appears that larger panels produce better bass response, but has this been quantified in any way? It also appears that a flat panel mounted in a stiff frame (similar to a framed painting) gives a flatter frequency response. Is that your opinion also?
Due to space restrictions I am considering putting panels against wall surfaces. Would you suggest some kind of cushion or absorption between the panels and the walls?
Finally, I have at my disposal a variety of hardwoods and softwoods that can be used to make flat panels. In your research have you read accounts of solid wood being used to make DML speakers?
Thanks for your attention to my questions, and thanks again for your work on this thread.
I have been intrigued by DML panels for some time and am considering a bi-amplified version with a large flat panel crossed over to a conventional sealed-box bass driver. In your research have you come across any rules of thumb for flat panel size and low frequency extension? It appears that larger panels produce better bass response, but has this been quantified in any way? It also appears that a flat panel mounted in a stiff frame (similar to a framed painting) gives a flatter frequency response. Is that your opinion also?
Due to space restrictions I am considering putting panels against wall surfaces. Would you suggest some kind of cushion or absorption between the panels and the walls?
Finally, I have at my disposal a variety of hardwoods and softwoods that can be used to make flat panels. In your research have you read accounts of solid wood being used to make DML speakers?
Thanks for your attention to my questions, and thanks again for your work on this thread.
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well DMLs are not conventional loudspeakers. And yes NXT types operate not on trying to eliminate resonances but on encurraging them with control. very carful balance of material properties to get level response.
Resonances are really only a bad thing when non linear across the range. Linear spring bending modes over a wide freq range will result in low distortion and generaly high sensativity.
The diference in mass between panels and film is huge.
Resonances are really only a bad thing when non linear across the range. Linear spring bending modes over a wide freq range will result in low distortion and generaly high sensativity.
The diference in mass between panels and film is huge.
JMC luthierie has a nice looking product which is clearly "proud" of the rear wall. It also appears gently curved which creates a cavity behind the assembly.
https://youtu.be/NTfl7o5xbyI
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https://youtu.be/NTfl7o5xbyI
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Agreed that the fun is in the building and experimenting.
The main reason for the first handful of posts in this thread, in particular the ones talking about sourcing carbon fiber from scrap and honeycomb from radiator protectors, was to show that the current ideal materials may not be as unobtainable as has been assumed. Total cost for two panels with Dayton 40W exciters is around $100, and is not particularly hard to build. With that said, lots of people are happy with the results from cheaper and easier to find materials.
Birch and spruce are probably particularly good woods to try. I'd also be interested to find out how the curve affects it. Is there a characteristic difference in sound between arch top and flat top guitars that we might speculate would either color full range sound or allow it to come through more clearly?
You're welcome, hope you enjoy it.
Sort of. Let me see if I can dig up some links. I'm about to take off for a New Years brunch and will be able to offer some more later.
Tectonic's "DMLs Explained" tech doc talks a bit about it:
http://cdn2.hubspot.net/hubfs/449794/DMLs_Explained_-_Short_Version.pdf?t=1482293437245
"For those who have the notion that a DML, being a modal object, would only work well in the higher frequency range, psychoacoustic research has shown that, in well designed DMLs where modal distribution has been optimised, above 2 to 2.5 times the fundamental bending frequency of the panel, perceived sound is indistinguishable from a perfect non-modal source. For example, an A4-size DML may have a fundamental mode at 100Hz and in practice be usable from 200-25 0Hz upwards. "
There's a tradeoff here between bass response and sensitivity. IIRC a thicker panel will generally get better response but in proportion to the increase in mass will have lower SPL at a given input volume.
Kuonan Li's thesis was one resource that I think I remember had some useful theory about this: http://publications.lib.chalmers.se/records/fulltext/154618.pdf. I'll dig back through there and see if I can point to specific parts that would be useful to that analysis later today.
That is audibly true at lower frequencies where simply holding the long edges of the panel tightly in your hands can make the panel go much lower before reaching a level of excursion that produces self-noise (flapping sound). I haven't been able to measure yet though, so the exact behavior and higher frequencies are both a mystery.
I just got moved into a new place and am in the process of unboxing though. I have a Dayton mic on hand. We'll see some measurements soon. I also have some foam board and weather stripping that I think will work for mocking up some frames - not very stiff, but I think we're mostly interested in damping rather than a rigid hold. We'll see anyway.
Yes, I would. Just a layer of foam behind them ought to help. At the very least, you need to protect the exciter from rattling against the wall or it will sound awful.
A bit of foam will also probably help damp high frequency output from the back of the panel from reflecting off the wall and back through or around the panel. I've experienced something like this as an excessively airy sound with the panels sitting loose on my desk in front of my regular speakers. The highs sound excessively airy, like arpeggios and castanets and stuff that I've heard through other speakers as being fairly dry suddenly sounds like they have a bunch of reverb on them. I solved that temporarily by putting throw pillows behind the panels. Permanently mounted foam in a frame seems like it ought to help the same way.
Well, there's the example here: http://www.diyaudio.com/forums/plan...panel-construction-project-2.html#post4932372. I've also read of people using birch and I think spruce. Harder is generally better, as a proxy for bending stiffness (Young's modulus) of the wood. Again, I'll see if I can dig up a reference later on why and how that factor matters... IIRC it's directly related to the speed of sound in the material. In any case, here's a table with values for various woods: PHYSICAL PROPERTIES OF COMMON WOODS. Keep in mind it also depends on whether you're parallel or perpendicular to the grain.
Good luck.
I don't know enough about guitars or DML to offer any more than a guess.
Let's just say that i like curved things and the JMC people built their DML as such.
Again, only guessing, I suspect a flat top kit would be a simpler starting point if thickness of the panel should be held constant.
I'm most intrigued by Joppe Pellen's efforts where he incorporates a center motor from a Rubanoide to flanking panels. It bears mentioning that the only viable application of DML incorporates a large ribbon tweeter.
Joppe's design elegantly eliminated one part.
He carefully applied clamping bars to get similar amplitude response between nodes.
I think the breakthrough from Tectronic was in the materials used to build the panel, which took nearly a decade - hence my suggestion to try something ready 'off the shelf'.
It appears such a simple device, but there's ONLY one maker that's managed to build one.
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Hmm... it looks like I've got high vs. low frequencies vs. bending stiffness exactly backwards:
https://riunet.upv.es/bitstream/handle/10251/3347/tesisUPV2873.pdf
https://riunet.upv.es/bitstream/handle/10251/3347/tesisUPV2873.pdf
I think that's referencing AES E-Library Model Optimization of Distributed-Mode Loudspeaker Using Attached Masses. Anyone got access to that paper that can post a summary of findings, and whether that process is feasible for any of us DIYers to reproduce? I have not tried adding point mass to my panels.
I should probably get back to unpacking my moving boxes at some point soon though if I'm ever going to get any measurements out of the panels I've already got...