Thank you for this informative experiment and measurements.
I would have guessed that Sorbothane would perform better than Poron. Of course, Poron comes in various different types and properties. Clearly the damping of a dml panel is more than just about the mechanical absorption of energy and I must confess – I have not studied all the posts in this thread (yet). The rate of absorption is probably different for each kind of foam (and depends on thickness too). But I was wondering about another characteristic. I read that certain Poron foam varieties are lightweight and are well-suited for absorbing sound waves. Could that be why you are getting good/better results with thicker Poron foam? Absorbing some sound waves around the edge of the panel?
I am hoping to build more DML panel speakers early next year, and I am considering using latex rubber as damping. But I might change my mind after Eric's post.
Anyway – I have not seen mention of the ODA panels on the main DML thread yet but have a look at how these guys mount/suspend their panels. Looks like ½ inch (or thicker) weather strip on the corners. I am sure they got the idea from Veleric, who was one of the pioneers in mounting panels with double sided weather strips to a frame.
ODA speaker system website:
https://andysigler.com/products/oda-speaker-system/
These panels look much too small and too square to my liking. Also the exciters (Dayton Audio DAEX25X4-4 Bullfrog Vented Disc Spider) looks much to centered on the panel. Wonder what they sound like?
Thank you for the link Twocents.
Those ODA speakers were pointed in the thread : Oda wood planar speakers. Not many information.
Somewhere it is said "3LP box" which is about 31.5cmx31.5cmx3.5cm
The structure in the picture you posted is interesting.
If the membrane is thin and orthotropic (like a 3 layer plywood is for example), this speaker may no be too small and too square.
There is a video showing the displacement.
Seems also M Zenker is cited in the development.
Christian
If they're doing wood like that, one would think a lot could be learned from the top of an acoustic guitar. That can be solid or laminate, it has patterns of bracing (that doesnt just hold string tension) all of which contributes significantly to the sound of the instrument. With the idea being that if you can get a good laminate to sound on par with a solid wood, if you can arrange bracing in such a way as to enhance the sound - all problems / issues common to driving a wood panel with an exciter - versus taught strings.
It's interesting how they take that exciter, plop it onto the back of a piece of wood, suspend that in a frame, make it pretty and - 1000 unit bet product! I like how they show "how it moves". Yeah.
The thing is that the top of an acoustic guitar has to fight against string tension as well as acoustic efficiency. And these two factors oppose each other.
A thin belly is loud and dynamic, but the bridge will bend upwards after a while. Hence bracing to prevent this bending.
But the bracing also has to transmit sound from the bridge to the whole soundboard, so it has to be similarly lightweight but very rigid.
Lots to learn. It's a magnificently complex integration of art and science.
A thin belly is loud and dynamic, but the bridge will bend upwards after a while. Hence bracing to prevent this bending.
But the bracing also has to transmit sound from the bridge to the whole soundboard, so it has to be similarly lightweight but very rigid.
Lots to learn. It's a magnificently complex integration of art and science.
I actually (I think...) tested resonance of a guitar top/body strung and unstrung and was surprised that it's not that different. I mean, it's not like resonance goes up to a crackly crunch with the increasing string tension. Fascinating, as Mr Spock would say...
I'd expect as DML speaker panels approach their limit of what can be done and how it's properly done, they'll share that.
twocents,
You're most welcome, my pleasure.
I too was surprised that the Sorbothane wasn't better, based on its reputation. But the data is the data....
Regarding the Poron, you are correct that there are many grades. The one I used is 4790-92 (Slow Rebound), which comes in two densities (12 or 15 lb/ft3). I used is the 15 lb/ft3 version, but I doubt that they are much different. Also, I actually do believe that the damping effect from the poron is indeed mainly due to the mechanical absorption of the panel energy and not the absorbtion of airborne sound waves.
Thanks for the Oda link. Interesting. It would be fun to think they got their mounting idea from me, but I doubt it. From the way that panel moves in their video, it looks like the support is much more compliant than anything I've ever used. But it would be interesting to know more about the panels (number of layers, thickness, etc), and suspension. But it would apparently cost $299 plus a $79 subscription to find out. At least according to this from 2020:
https://www.google.com/search?sca_e...4kEHZffBhMQzmd6BAgVEAY&biw=1920&bih=931&dpr=1
My gut feeling is that it's more gimmick than substance at least from a sound quality perspective. But it would be fun and pretty easy to copy, especially if we knew a few more details....
Eric
In this earlier post I described my "anti-xylophone" and showed how I used it to compare the damping performance of several materials.
https://www.diyaudio.com/community/...ing-of-dml-speaker-panels.394465/post-7258557
In those tests I used a "close mic" to sense the peaks due to the natural frequencies. It worked pretty well, I thought. But since then I have built my REW impedance jig and learned how to make electrical impedance measurements, and confirmed that the peaks in the impedance curves correspond to the natural frequencies of the panel (or beam). So I thought it would be interesting to try comparing different damping materials again, still using my "anti-xylophone" test unit, but using impedance to compare the damping instead of the "close-mic method". As it turns out, it works pretty well, perhaps even better than the original test.
Some example results are shown below, for three different damping materials. In particular, the impedance data is much smoother than the previous data, especially at the low frequency end, so it allows a better assessment of the low frequency damping performance than the earlier method.
As in the previous version of the test, smaller, wider, peaks should be an indication of better damping. So the results below suggest that the EPDM and Poron are similar below 400 Hz, but at higher frequencies, the Poron is a better damping material. Interestingly, however, the 3M 411 tape, performs a little better than both of the others at 80 Hz, but worse than either of the others at higher frequencies. The good performance of the 3M 411 at the lowest frequencies was something I would not have been able to see in the old test, since the results below 100 Hz were too weak and noisy.
All the tests were made using a plywood beam (5 ply), 16.25" long and 1.5" wide. Each curve below actually represents the average of 8 individual measurements, with the exciter placed at 8 different spots along the length of the beam (center, 1" offset, 2" offset,....,7" offset). Placing the exciter at different positions ensures that all the natural frequencies will be excited/sensed.
Eric
https://www.diyaudio.com/community/...ing-of-dml-speaker-panels.394465/post-7258557
In those tests I used a "close mic" to sense the peaks due to the natural frequencies. It worked pretty well, I thought. But since then I have built my REW impedance jig and learned how to make electrical impedance measurements, and confirmed that the peaks in the impedance curves correspond to the natural frequencies of the panel (or beam). So I thought it would be interesting to try comparing different damping materials again, still using my "anti-xylophone" test unit, but using impedance to compare the damping instead of the "close-mic method". As it turns out, it works pretty well, perhaps even better than the original test.
Some example results are shown below, for three different damping materials. In particular, the impedance data is much smoother than the previous data, especially at the low frequency end, so it allows a better assessment of the low frequency damping performance than the earlier method.
As in the previous version of the test, smaller, wider, peaks should be an indication of better damping. So the results below suggest that the EPDM and Poron are similar below 400 Hz, but at higher frequencies, the Poron is a better damping material. Interestingly, however, the 3M 411 tape, performs a little better than both of the others at 80 Hz, but worse than either of the others at higher frequencies. The good performance of the 3M 411 at the lowest frequencies was something I would not have been able to see in the old test, since the results below 100 Hz were too weak and noisy.
All the tests were made using a plywood beam (5 ply), 16.25" long and 1.5" wide. Each curve below actually represents the average of 8 individual measurements, with the exciter placed at 8 different spots along the length of the beam (center, 1" offset, 2" offset,....,7" offset). Placing the exciter at different positions ensures that all the natural frequencies will be excited/sensed.
Eric
The 8 individual curves that go into the average look like this (the Poron 92 case). The peaks below 40 Hz are those of the exciter itself, while the remaining peaks are the natural frequencies of the beam. The position of the exciter on the beam influences the exciter's natural frequency. Likewise the exciter's position has a significant effect on the fundamental frequency of the beam (at 80 ish Hz), but virtually no effect on the higher order natural frequencies.
Eric
Eric