We just had a big flat-screen tv go black on us, and being the inquisitive person I am, I completely disassembled it. There is a very large light-producing panel, followed by a hard plastic but flexible white translucent sheet the size of the screen, used to uniformly spread the white light across the screen, then a clear sheet the same size. I haven't had to time to test them yet, but it looks like they might be good material for DMLs. They are about as thick as card stock and a bit more flexible. Any thoughts on if they would be good materials to use? They're free and if they work, there is a ready supply of them to be had at the electronics recycling yard for free. It will take undoing a lot of screws, but free is free.
Some of my best results so far have been with EPS skinned with Kraft paper. Kraft paper is quite heavy though (95gsm) and has nice damping properties depending on the adhesive. It seems this very thin paper might be very interesting. Lighter, and maybe different damping properties.
The only reason I don't use paper skins is because the finish is fragile and subject to damage from gefingerpoken from das rubbernekkin. I'd have to put a grille over it for protection purposes.
The only reason I don't use paper skins is because the finish is fragile and subject to damage from gefingerpoken from das rubbernekkin. I'd have to put a grille over it for protection purposes.
Do you mean "DAEX25FHE4 Framed High Efficiency 25mm Exciter"???
https://www.daytonaudio.com/product/1177/daex25fhe-4-framed-high-efficiency-25mm-exciter
https://www.daytonaudio.com/images/resources/295-224--dayton-audio-daex25fhe-4-specifications.pdf
I get nice highs with these exciters on EPS and Polyfoam. Hybrid's as well, wood/EPS.
JohnnoG
https://www.vegware.com/uk-en/page/our-materials/#materials-plants
I came across this tea cup lid Made by vegware.
Although it says it has a shelf life of about one year.
Steve.
https://www.vegware.com/uk-en/page/our-materials/#materials-plants
I came across this tea cup lid Made by vegware.
Although it says it has a shelf life of about one year.
Steve.
Attachments
Just putting this idea out there for comment:
I think this is what's happening with the whole bandwidth vs efficiency problem.
The simulation below represents different system Q's (Quality factor) for the same cut-off frequencies. I think the Q is analogous primarily to the density and weight of the panel. The highest efficiency and narrowest bandwidth seems to correspond to very lightweight panels—EPS, XPS etc— and the seemingly widest bandwidth corresponds to heavier panels such as plywood, glass and acrylic.
The top end of the response can be extended by using harder panel materials, and the lower end can be extended by larger panel size and the correct edge damping. But of course the harder materials are generally heavier too, and so the general principle seems to stay the same.
Unfortunately I've blown up the mixer that I was using to phantom power my measuring mic, and I cannot prove the above. So I've resorted to modelling the curves while I look for a replacement interface.
I think this is what's happening with the whole bandwidth vs efficiency problem.
The simulation below represents different system Q's (Quality factor) for the same cut-off frequencies. I think the Q is analogous primarily to the density and weight of the panel. The highest efficiency and narrowest bandwidth seems to correspond to very lightweight panels—EPS, XPS etc— and the seemingly widest bandwidth corresponds to heavier panels such as plywood, glass and acrylic.
The top end of the response can be extended by using harder panel materials, and the lower end can be extended by larger panel size and the correct edge damping. But of course the harder materials are generally heavier too, and so the general principle seems to stay the same.
Unfortunately I've blown up the mixer that I was using to phantom power my measuring mic, and I cannot prove the above. So I've resorted to modelling the curves while I look for a replacement interface.
This somewhat matches my experience.. Using thin but relatively heavy 5 ply Blackwood resulted in a reasonably flat and extended response over that of Poplar, particularly at the LF end, but at the expense of lowered output levels, to the point where I put it aside.
Eucy
Hi André
In DML, The efficiency and the HF extension (low pass) seem linked as you mention.
The LF extension is driven by the geometry (larger panel, lower resonance). In a certain way, even if there are some limits, the area is a variable that comes in addition to the material.
At this step, I won't choose a band pass (my understanding of what you describe) as model but more as a product of a low pass (efficiency and HF extension) and a high pass (area driven).
Christian
Just joined and very interested in this topic but have a lot catching up to do. So rather than show my ignorance and not sure if it has been posted. But there may be some interest in thin layers of this material.
https://www.scientificamerican.com/...-speeding-bullet-mdash-it-rsquo-s-super-wood/
https://www.scientificamerican.com/...-speeding-bullet-mdash-it-rsquo-s-super-wood/
Agreed. The model I presented is simply a combined HPF/LPF, with the passband Q's adjusted from around 0.7 to 1.2 (just to make the curves look nice.)
The background to the example comes from designing double manifold sub-woofers. I noticed that the efficiency/bandwidth product in double manifold subs seemed to reflect exactly the same problem as with DML panels.
Hi Andre
Can you show the frequency for reference?
The composite board shared by @jamienelson before should be the right way
I have tested different densities of EPS stacked together
The frequency band of the loud volume has been widened
The above is for your reference~
But the material I have is too small
So there is no way to continue testing
@homeswinghome @toddincabo
Then I am more curious about the shape of "ears" and "irregular"
Does the shape make the frequency response flatter?
Have you done any testing on this?
Thanks everyone for sharing~
I used the spring-steel spider Tectonic TEAX32C30 drivers for both of the panels below. They are expensive drivers, and seem to have a better HF than all of the Daytons I've tried so far (0.1mH inductance!) but I was not impressed with their buzzing and rattling that I had to deal with.
I've tried several different shapes. This star shape was okayish. I had been working on baffle diffraction simulations for the tweeters on an open baffle system for a customer, and this shape was very good for a baffle. So I thought I'd see what the results would be as a DML panel of the same dimensions. This was a foam-core paper panel.
Ovals are also quite good, but driver positioning is more critical than for rectangular panels.
This one was a single sheet of polycarb TwinWall, 900mm x 400mm, glued to a single sheet of 10mm EPS of same shape and size. Of course 2nd-harmonic distortion was too high because it's all unbalanced due to the elasticity/compressions of the front and back faces being asymmetrical.
These are both rabbit trails worth further investigaton. The oval needs to be put into a symmetrical construction and re-tested and optimised if the FR is good enough.
Looking at these old files, maybe I should test Tectonic drivers again. Maybe I got duds the first time.
I learned a new knowledge "inductance" and "high frequency" today...
I just happened to be testing "Edge", "Basta" today...
But I want to put an OB tweeter on it first
Wait until the DML high-frequency test is completed before replacing it.
Not happy listening to music every day without good high frequencies
How to judge "Second Harmonic Distortion"?
Waiting for your good news~
Thank you so much for sharing~
Those who think their ears are the best judge of speaker performance might comment on the "warmth" of the sound when they hear even-harmonic distortion.
Guitar over-drive circuits are made to produce 2nd and even harmonic distortion... And maybe Beethoven's fifth might sound better like that, maybe not. I suppose it depends what one likes.
Measurements will expose different kinds of distortion better than the ear will.
Hi André
Would you share more data about this EPS skinned : EPS density, thickness, glue, glue quantity, final weight, frequency response in HF ?...
Thank you
Hello Xsuper,
Few tests for now on my side with this "ear" shape but no evidence of a big advantage. To be continued.
I forgot to comment on your ear shaped design when you posted it a while back.
Bertagni came up with that shape and if not mistaken was licensed to Yamaha. In both Bertagni and Yamahas design the ear shaped is used as a mid/woofer. That shape is not intended to be used for higher frequencies.
Bertagni came up with that shape and if not mistaken was licensed to Yamaha. In both Bertagni and Yamahas design the ear shaped is used as a mid/woofer. That shape is not intended to be used for higher frequencies.
Poor old trees!!!...We can't grow enough of them now, let alone if we make more stuff from wood!
And what an indictment on the human race that the making of bullet proof vests is a testing priority..
Note that it doesn't stop bullets quite as well as Kevlar, but it only costs a fraction as much... So who gets the Kevlar vests??
Ah me oh my