May be in an identical environnement, but not acoustically treated, not the same radiation pattern, some with wave-guide other without, and, by definition, resulting in a quite different interaction with the listening room and obviously not the same perceived sound !
Good luck to you too...
No I have not used the puck Solution in my first speakers,the smaller ones with only one exciter.
I have one version where I integrated a 25 mm x 2mm circular carbon fiber piece in the sandwich where the exciter is located (the exciter has a 25mm voice coil). So instead of CF skin - balsa-CF skin there is CF skin- CF - CF Skin . The intension was to connect the exciter directly to the front CF skin without adding to much weight.
It is I, who asked you about the puck. It is to get rid of the standing waves from interfering. Thank you for the info. Can you tell us about the angled incisions around the perimeter in your Göbel clone? Thanks.
I have not seen any Goebel patent that explains the "9 layer" construction. I fear that it is creative accounting.
It seems to me to be a 3 layer composite, balsa core with cf/epoxy skins, and perhaps a thin finish coat for appearance and UV protection.
But maybe they count like this:
balsa core in the center, plus these four layers on either side:
epoxy
fiberglass (or carbon fiber)
epoxy
finish
which makes 9 altogether.
Or maybe they consider the fiber/epoxy layers to be a single layer (as most would), but count the pore filler as a layer, and apply the finish in two coats which they count as individual layers. But I'm just guessing.
Anyway, you can see them being made here;
this was obviously from the time before they switched from fiberglass to carbon fiber for their skin layers.
I just watched it again and realized that they might be using the same trick that I suggested to @Sandasnickaren a few posts ago, That is to drill small holes in the balsa layer to allow excess epoxy to flow through the board and into the absorbant batting. The holes are the dark spots in this image from the video, I suspect.
Eric
Thanks!
I think you are guessing well.
From the photo you posted, it looks like the balsa is perforated. I haven't watched the video yet, though. I read somewhere that they are using heartwood for the membrane.
I don't recall those three and could find only one:
https://patentimages.storage.googleapis.com/a3/b2/ea/04d6bf69de7f1a/GB2031691A.pdf
which seems to be related to piston speakers, not DML. I just skimmed it but noted that they consider the index of merit to be E/rho for that application, rather than E/(rho)^3 as for efficiency of a DML. So weight is important for that application too, but not as important as for a DML.
Eric
Thepurpose of the incisions is to reduce (trap) the reflections from the edge of the panel. I’ve tried with and without and there is a massive iprovment with the incisions. The panel is also glued to a soft rubber that also reduces the reflections. I’ve tried to enclose the edge with rubber as per goebel it didn’t make a noticable difference in sound. But it looked really uggly😉.
I just copied the göbel incisions.
Interesting. I always wondered if they made much difference. I did saw similar incisions in a plywood panel once but wasn't impressed with the difference. But at that time I was an extreme novide and didn't really have any idea how to look for the effect.
Eric
Tagis,
when you say recording. Do you mean a regular sound wav file?
How do you intend to analyze it?
Or?
I Google-translated part of the transcript of that video,
-------------------
fine resolution and speed far superior the membrane of the bending wave converter consists of an exotic precious wood mixture which, due to its specific properties, forms the prerequisite for the natural sound of the Göbel bending wave panel. in a highly developed pressing process, this core material is optimized with a new layer structure which gives this highly sensitive natural product not only the damping properties relevant to the sound, but also the best resistance to aging. another measure that gives the Göbel bending wave transducer its natural sound are the cuts on the edge of the membrane, since the precisely calculated angle geometries must be correct to the hundredth burned in with a computer-controlled reader in this step the heartwood is sealed airtight at the same time in a last step the read membrane is encased with a special combination of aluminum silicone rubber and ndf sst so that there can be no reflections at the outer edges, so that we can meet our high standards and be able to guarantee outstanding quality,
----------------
I don't know where to put the punctuation marks, though. Do you catch anything?
From the video, I think the balsa sheets are glued horizontally.
Its called hands on experience you could learn a lot from doing it.Oh, alright. The blind man's method.
I noticed that too about the perforations. I don't know exactly what to think of the first picture, where there are no apparent perforations. In fact, it doesn't really even look like end grain balsa. I wonder if that is just a "staged" video clip that didn't use an actual or fully prepared panel for some silly reason. As if they decided they wanted to include a shot of that only after the rest of the video was prepared, and they didn't have any of the right panels handy, so they "faked" it.
There's no reason I can think of that the black spots would be on the fiberglass.
I also don't think the grain direction is different. It's just a bit of balsa thats different in color. Those balsa panels are made of an array of balsa pieces that are perhaps 50mm x75mm glued together on the edges, and not "strips". I don't know for sure, but I suspect they take a bunch of balsa boards that are, say 50mm x75mm x 600mm(?) with the grain running in the long direction. Then they glue them together on the short sides to make a big block and then slice the block into thin panels. That's my best guess anyway.
Eric
And an even thicker monster panel!
from here:
https://patentimages.storage.googleapis.com/d7/c4/c9/cbd405fcdd75ae/US3247925.pdf
from here:
https://patentimages.storage.googleapis.com/d7/c4/c9/cbd405fcdd75ae/US3247925.pdf
The ignore button has been pressed
My chladni experiments on glued strips also show increased activity at the seams so the joins in all the small pieces of balsa introduce internal reflecting boundaries which affect wave transfer across and through the panel depth.
Also, what if any is the result of the differences in sound velocity between the balsa core and the CF skins?
All very complicated and little understood I believe
Eucy
There's another complicating factor here and that concerns introducing internal reflections from the core penetrations. It also is a factor in corrugated panels like corflute and cardboard.
My chladni experiments on glued strips also show increased activity at the seams so the joins in all the small pieces of balsa introduce internal reflecting boundaries which affect wave transfer across and through the panel depth.
Also, what if any is the result of the differences in sound velocity between the balsa core and the CF skins?
All very complicated and little understood I believe
Eucy