Currently I´m pursuing a better hf response so the baffle size is not significant
A 2 um foil will mean a too high resistance, around 16 ohm. And, as you said, it is impossible to handle.
Made a membrane with 8/2 folding ratio and 5/5 alu ratio, approximately 4 ohms (blue with a wave guide):
Still no better hf response although lf response was extended.
I guess the depth of the folds, 8 mm, turns out to be a Helmholtz resonator.
If that is the case, next try with 6/2 folding ratio (that is, 6 mm deep pocket) and 4/4 alu ratio will show a better hf response.
An externally hosted image should be here but it was not working when we last tested it.
Still no better hf response although lf response was extended.
I guess the depth of the folds, 8 mm, turns out to be a Helmholtz resonator.
If that is the case, next try with 6/2 folding ratio (that is, 6 mm deep pocket) and 4/4 alu ratio will show a better hf response.
These types of foil can be found in Denmark and Norway as "frokostfolie".
One type (rul-let) with 7 um alu has a paperback that can be removed by water and another (Vita) with 10 um alu has a peelable paperback.
Look for them in super markets.
Doh. I was looking for them in India. I guess 7um is preferred? Which membrane won your shootout? I guess there is still no clear winner since you are making new designs still.
If you use a waveguide instead of EQ you will improve the fidelity as the distortion will be much lower. And the directivity and soundstage improves also...
Picture shows the first prototype with AMT "midrange" and AMT "super tweeter" in a CNCed Corian waveguide, and three 8" drivers in a combined CNCed Corian baffle / basket..
I compaired homemade waveguides for the TPL-150. I prefer a straight wall, using 15cm wide wooden planks, instead of a waveguide based on the curvature of the Avantgarde Trio smallest horn, that is similar to yours. I angled the curved walls more open than the Trio horn. I used the same waveguide for a 50cm true ribbon, that is better at frequencies 5000Hz and up, and here the curved waveguide works better.
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I don't like the TPL-150 above 10kHz anyway. Maybe you should consider True Ribbons crossed at 3-5kHz? Much lighter membrane and produces HF perfectly.
I remembered something from my ribbon mic project. Someone wrote that they treated their aluminum foil first by gently hammering out imperfections, using a cloth as protection on top of it. It did not really work with 2 micrometer foil, but worked great with kitchen foil. That did not matter since kitchen foil was too thick for ribbon microphones but it is not for speakers. It may improve sound slightly.
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Yes, the 7 um is the winner. But one has to take great care when cutting.
The angle of the knife is crucial, wrong angle and you have ripped instead of cutted.
The paper on 7 um is also more easy to get rid off, just soak it in water.
Yes, I have thought about that. I don´t see how it can easily be used with the diy AMTs using a folding tool and then bake though.
Again, the rationale for using a wave guide is for me to get better lf response.
Hopefully it will not affect the hf response too much.
But it is still work in progress.
Changing the verdict; the whole process starts with the cutting and the high friction paper of the 7 um foil makes it too error prone.
Even if the peeling off with the 10 um foil is more tedious the "oily" paper is not error prone when cutting, so the overall yield is better with the 10 um.
BTW, I´m using an Xacto #16 blade on glass and not a rolling knife; a rolling knife doesn´t give the control needed.
I would use a rubber hammer, hitting the aluminum foil repeatedly with a cloth as protection. I don't mean you should hit it when it is in the finished membrane. Do it before you do anything with the foil.
I have experienced and have read from others that waveguides, like the standard one for TPL-150, gives distortion to high frequencies, maybe because of compression, like in the compression driver horn. Or, it focuses the sound, and you can better here the distortion that was already there, due to increased volume. Or a combination of the both.
Doesn't matter, I was in both Rimi and Meny in Oslo and found neither. They just have regular aluminum foil. Would you care to sell me some paperback alu leftovers?
It is hard to get the embossing done that way, the paper is too thick.
And when the film is applied any remains are wiped out as the film has to be rubbed to the alu. In the folding tool the surface is even more flattened.
Maybe the rods in the folding tool can be embossed, but then you´ll have to match positive/negative embossing.
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