Sorry - I dont get this - it seems a bit contradictory - "nothing sticks to mylar" vs. "demolish half press to get PU off mylar"...
Please explain...
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Andre,
I agree 90%. The only part I'm not so sure about is the part I bolded. I'm pretty sure the apparent elastic modulus of a laminated composite will always be less than its stiffest component. For example, a CF/Foam/CF composite won't be quite as stiff as solid CF. The main advantage of the sandwich though is that it can be nearly as stiff (especially in bending), but much lighter. Which is great for airplanes and tennis rackets and perhaps even better for DML panels.
Eric
Andre,
Have you tried Dyneema with epoxy? I'm not familiar with it (until now). It's low density is interesting, and some quick modeling suggests it could be about equivalent to CF/epoxy at similar thicknesses. And it looks like it's available at lower weight than CF fabrics, which should be an advantage. But I don't see it sold by composite suppliers (who sell CF and FG). Rather, it's marketed as a fabric for sails and camping gear and the like. I'm wondering how/where to buy it if I want to use it like a composite reinforcement rather than a "fabric". Any thoughts?
Eric
Thanks for that Eric.
You're probably right... A soggy piece of fabric glued to a floppy piece of EPS becones a hard board when cured, which is counter-intuitive. But you're pointing out that the elasticity of the individual materials does not change.
I got sample quantities from UTEK Composites on China.
https://www.utekcomposites.com/tag/keyword/33400
I'll send more detail when I get back to my computers.
You have to really dig around on that site to get to the ultralight weight stuff.
They call it UHMWPE-- UltraHighMolecularWeightPolyEthylene.
Polyester resin does work with it, but the fibre itself does not take easily to adhesives. It's very slippery, so it must be fully embedded in the resin.
Perhaps a woven material is preferred as it will be much easier to see that no air is trapped in the joint... poor contact between the skin and core is probably not good...
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It's similar when anything with thickness is bent . Compared with it's centre line the surface on the outside of the bend is stretched and the surface on the inside compressed. That then has the expected effect on the inner material of a sandwich which also suffers the same thickness effects.
@Veleric
Eric have a look at this MadeInChina website.
https://utekcomposites.en.made-in-c...-for-Safety-Protection-Protective-Helmet.html
This is where I originally found Utek and chatted with their sales people (very helpful, very polite). They specially prepared ultra-lightweight samples for me.
Just a heads-up: I'm not sure how inquisitive the URL snoopers are in different parts of the world, but Utek manufactures these lightweight high-strength fabrics for use in bullet-proof body armour, explosion-proof webbing and police riot gear. You might get somebody in a suit and dark glasses with a bump under his armpit knocking on your door asking questions?
Did anyone consider a rubanoide style of ‚dml‘ ?
I know this will never be Fullrange so this is the wrong thread.
But I just wanted to post this idea.
I made a very quick and dirty test model.
it is just a sheet of copy paper 15x20cm stuck on a dayton exciter.
this is in no way optimized. It leaves much room for investigating in best size, best material/coating, coupling, damping.
I think the rubanoide looks very promising.
even this one does sound quite nice
paired with an ob bass
I have allways been a fan of Linaeum speakers.
I know this will never be Fullrange so this is the wrong thread.
But I just wanted to post this idea.
I made a very quick and dirty test model.
it is just a sheet of copy paper 15x20cm stuck on a dayton exciter.
this is in no way optimized. It leaves much room for investigating in best size, best material/coating, coupling, damping.
I think the rubanoide looks very promising.
even this one does sound quite nice
paired with an ob bass
I have allways been a fan of Linaeum speakers.
Attachments
Hi jamienelson
I have a question
Can you record the "Free No Load Curve" of this high frequency Exciter?
Record it at the same distance as "Triarm Shape"
I'm also thinking about how to test high frequency
Can you share your Exciter model number?
Thank you very much~
Hi Spassgeneral
Can you record the "Free No Load Curve" of this Exciter?
Thank you very much~
This was greatly promoted by member @chdsl, who has since disappeared. Starts around post #7,527. Search functions can help you.
yes I know, but all these are based on the self wound flat coil which makes it difficult to build. I coupled the paper to an exciter. Paper is much lighter than the dml panels regularly used. should give plenty hights. The curved shape gives some practical stiffness.
what is the free no load curve?
what is the free no load curve?
The Rubanoid drives the whole long edge of the active surface.
The problem in this design is that the paper is being driven by only one point. It looks like it cannot deliver bending wave action, and probably not HF.
It might work better if you used a light but stiff structure along the edges that touch the driver?
might work better if you used a light but stiff structure along the edges that touch the driver
yes, that is my intention. This is one of the things to elaborate. a proper coupling to the exciter. and also to fix the outer edges. This was really a 2 minute check if this is possible at all. exactly the paper is driven at two points as the exciter couples with a ring.
yes, that is my intention. This is one of the things to elaborate. a proper coupling to the exciter. and also to fix the outer edges. This was really a 2 minute check if this is possible at all. exactly the paper is driven at two points as the exciter couples with a ring.
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I'm very sorry that I described it too briefly
Exciter moves freely in the air and without any panels or paper
Then use the same distance to measure the SPL curve
Thank you so much for sharing
I feel that this approach is similar to "Air Motion Transformer Tweeter"
The difference between them is the number of folds and the direction of movement.
Air Motion Transformer Tweeter - Wiki