The current Tectonic panel, DLM500 has a 575x400mm panel according to the spec:
https://tectonicproaudio.com/wp-content/uploads/2022/05/DML500-Rev-07-Jan-22.pdf
0.3mm will certainly be close in absolute terms, but if tectonic uses for example 0.2mm skins that wont be very obvious visually, but is 50% thicker, which might be significant for efficiency. I only know that they mention that the plates are around 3.5-3.6 mm thick in one video, but I have not picked up anything regarding how thick core they use and could be anything between 3.0 and 3.4 mm. I got very thin carbon to be able to make composite with just over 0.1mm thick skins...but we see how that goes :\
I use 4xDAEX30HESF-4 per plate, using these plates treated very lightly with hide glue and shellac: https://www.dekokopf.com/neopor-styroporplatten-3er-set-50x33x2-5cm.html
I have 4 speaker stacks with 4 plates per stack, and one of the Sanway amps to drive each stack.
Thanks Eucy.
Concerning the frame material, it was material left over from a project at work, so I got lucky there. But indeed it is an unusual size, as it is 1" x 6" actual size. I like the contrast too. And it was indeed prefinished. But I decided I couldn't really live with the finish as it was. The original finish was intended to make the poplar look like some other species (who knows what), so it hid all the streaks of color in the poplar, and had a really lifeless matte finish. Ugh. I sanded off the top coat completely, but not the stain (as best I could). Then I added a coat of stain to add color to the areas where the stain was inadvertently removed, and added a coat of wipe-on satin polyurethane. I'm much happier with that finish than the original, which is visible in the construction pics, and in the backs of the completed speakers.
Concerning the depth of the frames: I can't say for sure that the frame needed quite that much bulk. But I can say that a frame made of 3/4" x 2-1/2" poplar was not stiff enough. With the latter material, the natural frequencies of the mounted panel were not what they should have been (based on FEM), and in particular, the lowest natural frequencies were more spread out than they were supposed to be. In order to achieve my objective of bunching up the lowest natural frequencies and minimize the resulting gaps between them in the frequency response, I needed the frame itself to be very stiff. Even with the 1" x 6" frame, I found the center brace on the back of the frame was critical to avoid that the fundamental mode separated too far from the modes directly above it. With the braced 1x6 frame, however, the natural frequencies matched the FEM results almost perfectly. I haven't noticed any significant negative effect of the frame depth, though I would not claim there is none. However, I routinely listen to these from both sides and don't notice much if any difference. If you stick your head inside the frame in the back, however, the base is awesome!
Concerning the exciters (DAEX25VT-4): My favorite exciters thus far have been the DAEX25FHE-4. I bought four of the VTs recently because they seemed similar but a little lighter and without the superfluous (for me) ears on the frame. In the FR comparisons I have done, the two are virtually identical. I still kind of prefer the FHE version for prototyping, but only because it's easier to attach alligator clips to the larger tabs on the FHE than the tiny tabs on the VT. For a final build, I like the VT but only because it looks a little cleaner.
Eric
Christian. yeah good questions.
I did coat the ply. My intention of course was to add minimal weight, while making them look nice and minimize how much they might warp due to changes in humidity. On the front faces I put 2 very light coats of tung oil finish and two coats of wipe-on polyurethane. On the back only one coat of each, except I added a second coat of the polyurethane in the area of the exciters. I like the area of the exciter to be very well finished. I think it makes the bond to the exciter better, but also makes the wood a bit stronger so it's not damaged if you have to eventually remove the exciter for some reason.
I used the original VHB. It has always worked well enough for me. I have not tried other methods (except double sided tapes for prototyping). I'm very leery of gluing an exciter on for fear that later I might want to take it off!
Eric
Eric
Have you considered using fibreglass tissue instead of CF?
It's very light, about 25gsm, and can be purchased cheaply in thicknesses from 0.1mm upwards
It may be a good balance in terms of stiffness to weight with a suitable core
Eucy
Eucy
Yes for sure. It is easier to get thin FG and inexpensive. I have tried it with balsa core with decent results. Definitely worth considering.
Eric
I tried fibreglass on nomex core. I had some demoulding issues, so only got a small plate to test, but that was not impressive at all and had low efficiency. Still learning the process and could be that it is possible to make good glassfiber plates, but my impression was that it is not worth pursuing.
Leob,
At first glance, I can't see why it would be inferior to CF unless it's too thick. CF is stiffer than glass, but may in fact be too stiff, and the bending loads applied certainly won't reach stress limits of either material. Did you use epoxy or polyester binder? The binder would conceivably have the biggest effect on the finished properties at low load levels
Eucy
EucyDome ...Final Episode 👍😁
After some unavoidable delay, I made time to reveal and detail the process involved and rather than draw it out in more teasing posts I've put it together in the document form attached
YRMV, but I do recommend you try it.
After some unavoidable delay, I made time to reveal and detail the process involved and rather than draw it out in more teasing posts I've put it together in the document form attached
YRMV, but I do recommend you try it.
I used laminating epoxy from easycomposites and managed to make the skin very thin...perhaps too thin. Certainly a lot of variables that has to be checked, but my initial impression was really that it was going nowhere in terms of result compared to effort and cost.
any advice on how to build a frame for my tectonic copy attempt? what to put on the perimeter of the carbon plate to isolate it and avoid vibrations and squeaking
You can look at the solution I use in my earlier posts. I used a 3D printer to make the parts needed for assembly though. I'll be happy to send you the files if you have access to a printer or could perhaps even help out with printing them for a reasonable cost.
I suspect the carbon composite plates will be quite different than the EPS plates I use when it comes to suspension required. I use self-adhesive foam strips to suspend the plate in the frame, and found that at least my thick EPS needs minimal suspension. Initially I had them clamped everywhere except for the corners, similar to how it looks like Tectonic does on DML500, but that resulted in reduced sensitivity and a very mid focused response. Now I just have 8 points per plate where I have 20mm strips clamping the plate from both sides which was a massive improvement.
I think tweaking how far those points are from the corners will give me some ability to fine tune the response a bit more when I get some time.
Regarding vibration, if you high pass at 90-100hz you be surprised how little the frame and even exciters vibrate. It is quite fascinating how they can blast at really high levels, and nothing but the actual plate seems to move. Sure, you need a solid construction, but the vibration stress on the material is nothing close to that of a conventional speaker where anything slightly loose will case audible squeaking.
Perhaps we should start a separate thread in the PA forum regarding DML PA systems?
thank you
any help with photo 3d models and more would be very useful to start understanding how to assemble everything, assuming that everything is fine as soon as the exciters arrive.
As for the PA specific forum it would be very interesting, it seems like a very good idea
My main advice is to try more than one different mounting technique. But that said, my preference is to attach the plate around virtually the entire perimeter (except the corners), using a double sided tape with good damping properties. And the only reason I don't go all the way to the corners is because if you go all the way to the corner it's really hard to separate the plate from the frame to try something different using the same plate and frame.
I've had pretty good success with these:
1) 3M Extreme Double Sided Mounting tape
https://www.amazon.com/Scotch-Extre...ocphy=9007449&hvtargid=pla-307252020700&psc=1
and
2) Butyl tape like this
https://www.amazon.com/Second-Skin-Multipurpose-Butyl-Rope/dp/B0155KELRW?ref_=ast_sto_dp&th=1&psc=1
The butyl tape I actually used was thinner (1/8" instead of 1/4"). I don't really know if one is better than the other. It probably depends on the plate. The 1/8" version is not currently available.
This is the one I used:
https://www.amazon.com/gp/product/B005UPLJCS/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1
For me the 3M stuff is slightly easier for me to get, as it's available at the big box hardware stores (Lowe's and Home Depot). In the comparisons I've done my impression is that the Butyl tape provides slightly more damping, but not a lot more.
Eric
Thank you Eucy
Very clear and seems not too difficult.
Thank you for the effort to put it in a pdf file format with the pictures.
Christian
PS : up date of the history file to come with all those last good posts
Thanks Christian
I hope a few will try it out and report back
A few extra points
1/ If your exciter is centrally vented you can use the vent to centre the exciter on the drilled hole using a fine stiff wire passed through the hole. In this case the exciter is attached prior to the dome
2/ There may be some tolerance in centring due to the panel stiffness
3/ due to 2/ above it may also be possible to use a 25mm dome on a 32mm dia exciter.
4/ Multiple exciters > multiple domes?
5/ Again due to the panel stiffness, the possibility exists (untested) for an array of domes surrounding a single one on the exciter axis. Totally unnecessary I'd venture to say but enticing to try 😜
6/ Fold-back testing.. To do this I peel off most of the masking tape leaving a top and bottom piece. While playing test music or tones you can peel the top tape off and holding it, flip the dome away and back again and you will hear the effect... Fingers and tape won't kill it as long as you don't put your fingers on the dome
7/ Whetstone alternative... Glue a piece of fine grit sandpaper or preferably wet and dry paper to a flat board. This can also be used on the edges in lieu of a file.
Eucy
Stiffness
I did some reading and regarding the question about stiffness and material choice; from what i understand mainly from this¹ paper I understand that material choice is always related to size and distance from the exciter from the edges. Again from what i understand is that this comes from two different effects; 1: the absorption/dampening from the material itself and 2; the transfer from panel to air. So if the question about material is always answered with CF or CF-sandwich as the best material to go to, the second question should be how big a distance is needed from the exciter to the edge to fully absorb or transfer all the energy for all frequencies? Because if there is energy left on the edges and gets reflected back onto the panel this can modulate other newly introduced frequencies.
Related to this question of size is the effect of waves traveling in the DML is not the same for every material, more important the speed is not the same for each frequency². It appears that lower frequency travel more slowly then 340 m/s, higher frequencies travel faster then 340 m/s.
If i interpreted this correctly it the following goals should be targeted: Balans between stiffness, absorption and size should be matching.
So in some cases it is better to choose carboard above CF. Correct or not?
Reflections/material impedance
Although problems related to reflections within the panel could also be solved by adding dampening on selective places, most probably on the outer edges. A second option could be to add or remove weight a few cm's/inches from the edge to induce a impedance matching towards the edges so the transfer to the air is optimized. (like an RF antenna that is engineered to transfer all energy into the air) The last options has the advantage with increasing the efficiency, the first option lowers the efficiency.
Simulate
To simulate, I asked some college's of mine specialized in FEM, the answer was simple, this can not be done by any free FEM software package on the marked. You need to use a professional tool with some expensive add-ons.
Experiment
So that leaves me with experimenting. The only thing i could think of is measuring the impedance of the transducer, unrelated to the material and size used, this should be resistive for each frequency. I also ordered some accelometers with the hope the don't add to much mass into the measurements. Maybe something optic should have been better..
¹ https://riunet.upv.es/bitstream/handle/10251/3347/tesisUPV2873.pdf
² https://publications.lib.chalmers.se/records/fulltext/154618.pdf
Hello Eucy
1/ good trick. here I made some tooling in 2 parts to improve the precision while gluing the exciter. Not fully satisfied. Your trick sounds more simple.
4/ For my applications, I am in the opinion of only one HF source due to small wavelength. So if multiple exciters, I would suggest one dome and a cross over to keep only one HF source. Answer for a PA application might be a bit different due to the power to handle and the more limited bandwidth (need of domes?)
7/ I am also on this idea