dit you try that alu tape i send you ? i wonder what weight you get with that with 12 mic mylar, the foil is a dream to cut! so far, almost all designs came off my plate. cant even remember i had a fail in cutting once. (prob did but out of the amount of tests i made thats great)
Ah, I missed that you sent some alu tape. That is the 14 um alu tape? After I decide what type of membrane backing I'll use I plan to play around more with the alu thickness.
I have some tests right now with 30 and 50 um thickness but I'm also interested in testing 25 um, so 14 could also be interesting.
But before that, I have made some membranes! I haven't measured them yet but so far, baking the 23 um mylar makes it hold corrugations! Without baking it turned into a mess as you can see in my last post.
Here are all the membranes I plan to test tomorrow:
Top blue-ish is the slightly heavy 9/12 composite.
Next 3 are 23 um mylar. The upper 30 / 50 number is the alu thickness. The 140 or 150 is the baking temperature except that the bottom membrane with 50 um alu was baked at 150 degrees, the number on it is wrong (I corrected it after I took the photo when i noticed the error)
All mylar membranes hold corrugations well, which is great! They feel pretty stiff, night and day difference when compared to the 12 um mylar, no bowing with crinkle noises when I push my finger in between the aluminum.
And the keen eyed among you might notice that the border is thinner than my previous plain mylar membrane. It was a bit heavy so I reduced it from 3.5 mm to 2 mm to reduce weight:
First is with 30 um alu, the heavier is with 50 um alu.
Here are some images of me preparing the stiffening aluminum sanwich. I used a fresh coat of ReMount glue on the surface under the 40 um aluminum before I cut it such that when I peel it away there is enough glue residue for it to stick to the membrane.
Here is above and below after corrugation:
After baking when peeling off the stiffening aluminum, worked great.
And since I now baked at higher temperatures I wanted to reduce the temperature error. By itself it varies by ~ +- 8 degrees which is more than I would like. But I could get it down to +- 1 degree by just watching the probe and if it got too hot, I opened the oven door just enough to drop the temperature down a bit. I only baked the membranes for 20 minutes so no problem to babysit it and adjust when needed.
OOh waaait !!! did you use 12 mic mylar as backing on all ? (except the laminate) then used a piece of alu just to hold shape while corrugating and baking ?
and since it is hot the alu just to hold shape can be peeled of easily since the remount has not stickyness anymore ? if so thats a nice method. i never seen mylar holding there shape that well !! that might change my method as well ! since i use coil all over the place to keep it stiff, this might work to have a little more mylar only increasing output.
those foils with only 30% alu look great !! i am stoked !! already !
and since it is hot the alu just to hold shape can be peeled of easily since the remount has not stickyness anymore ? if so thats a nice method. i never seen mylar holding there shape that well !! that might change my method as well ! since i use coil all over the place to keep it stiff, this might work to have a little more mylar only increasing output.
those foils with only 30% alu look great !! i am stoked !! already !
Exactly!
Although for todays 3 mylar membranes I only used the 23 um mylar I got from you. I did use the same technique with 12 um mylar on the membranes I measured 2 weeks ago though.
The 12 um mylar holds it's shape with 30 um alu, but is very floppy and buckles under even very light pressure. The 23 um mylar is a lot stiffer, feels as stiff as the aluminum composite backings so I have a good feeling it will measure great.
i bet you can get away now as well with thinner alu on 23 mylar, like the 15 micron alu i send you. that would be great. maybe not for a long panel but it will be for a small tweeter etc, maybe even thinner. but then we need to use spray glue.. witch might come off just like the backing with the remount, so i gues you need a rather nice stiff foilf as stiffner while baking.
interesting results non the less ! really cool ! i might try that with a tweeter soon !
interesting results non the less ! really cool ! i might try that with a tweeter soon !
Yup, the acrylic adhnesives can handle 150 degrees long term so can easily handle 20 minutes of baking. It is also very convenient to handle, sticks very well to the mylar and very easy to cut.
Thinner alu could work, but would be less efficient since more of the membrane weight, proportionally would be mylar.
But if the 23 um mylar measures as great as I think it will, then I might as well test with 15 and 25 um thick aluminum too and see how it compares. The efficiency will be less but maybe the other aspects will be improved?
Thinner alu could work, but would be less efficient since more of the membrane weight, proportionally would be mylar.
But if the 23 um mylar measures as great as I think it will, then I might as well test with 15 and 25 um thick aluminum too and see how it compares. The efficiency will be less but maybe the other aspects will be improved?
yeah without the baking , thinner alu becomes a problem if its less thick as the mylar.. (like 7 mic and 12 wont hold). in this regard it might work with 15/12 or 15/23 since it is set with a backing while baking. 15/12 would be most awesome. in ur case you might need the 23 to hold shape where there is no alu though. but nice tests !!
Yup, that might work.
The 30/12 baked didn't work, it had a huge dip in the top end.
But maybe that is because the aluminum is too heavy for the thickness of mylar? In that case the mylar weighs 35 grams and the aluminum weighs 72, so 2/3 of the weight is the aluminum. Maybe the problem will go away with thinner aluminum? I think it would be a problem problem if we try to push xmax with it since it will probably buckle but might work great higher up in frequency.
ah that looks like break up. so although it holds shape.. its not acting the same as alu and mylar holding shape. so for your huge gaps without alu, it might not be enough 🙁. you got a dip at 12khz. im pretty sure if you can get that unsuported distance down a little that would rise allot. or add a tiny alu trace (a useless trace) to get that dip out of the passband above 20khz
this is what i had with my rubber magnet panels, the distance between traces makes it do this. now since the mylar had sonme stiffness this is much higher then one would expect but it aint enought by the looks of it.
in my setup with rubber magnets it was a bass panel so not a huge deal, but the same was hapening in the tweeter panel but of course higher in frequency.
this is what i had with my rubber magnet panels, the distance between traces makes it do this. now since the mylar had sonme stiffness this is much higher then one would expect but it aint enought by the looks of it.
in my setup with rubber magnets it was a bass panel so not a huge deal, but the same was hapening in the tweeter panel but of course higher in frequency.
Huh.
If so, then I believe there should be another option: going with smaller magnets! Say going down from 5x3 mm magnets to 3x2 mm, but increase the number of rows to get the same width. The overall area of aluminum traces would be the same, but there would be more but thinner traces. The driver xmax would decrease, but that is probably less of an issue since we won't be pushing it that hard anyway.
And if you are correct that it is breakup then 3x2 mm magnets would push the breakup up to 17.5 khz, but might also eliminate it since now the overall membrane is a lot stiffer since there is less unsupported width.
A lot more magnets to glue though, but when has such things ever stopped me 😆. Might be fun to toy around with after the current planar is done.
We have a new champion!
All hail the baked 23 um mylar!
The polar plots, as I predicted don't have the big dip (the breakup?) that the 12 um mylar has. In fact, it measures great. Of well performing and usable backing membranes, it is the most efficient yet on the top end although the composite is slightly more efficient on the low end.
For my purposes, the efficiency is close enough:
Polars both look great.
And interestingly enough, if I bump the low end on the 23 um mylar membrane then the distortion is as good as the composite.
In conclusion, both are great and I can make a great planar driver with either, so I plan to go forward with the backing that is the cheapest and easiest to buy, and that is most likely the 23 um mylar.
Next is to test if the different baking temperatures made any difference + test varying the aluminum trace thickness.
All hail the baked 23 um mylar!
The polar plots, as I predicted don't have the big dip (the breakup?) that the 12 um mylar has. In fact, it measures great. Of well performing and usable backing membranes, it is the most efficient yet on the top end although the composite is slightly more efficient on the low end.
For my purposes, the efficiency is close enough:
Polars both look great.
And interestingly enough, if I bump the low end on the 23 um mylar membrane then the distortion is as good as the composite.
In conclusion, both are great and I can make a great planar driver with either, so I plan to go forward with the backing that is the cheapest and easiest to buy, and that is most likely the 23 um mylar.
Next is to test if the different baking temperatures made any difference + test varying the aluminum trace thickness.
More data!
I found no significant difference in baking temperature of 140c vs 150c, so I will probably go with 150c to be on the safe side since the acrylic glue on the self adhesive aluminum can handle the higher temperature.
Also, the 50 um aluminum traced membrane is 0.8 dB more efficient than 30 um, which is not a huge difference. And the distortion is mostly similar but a bit higher in the upper midrange.
In practice, both alu thicknesses work just fine so I might go with the one that is the most convenient based on other reasons. Like if I decide to split the coil and run it on both sides to make the shading network easier, then I'd probably use 2x25 um aluminum.
But if I only do one side the 30 um is easier to cut since my roll is 50 cm wide vs the 50 um alu tape which is 7.5 cm wide. The wider roll can easily handle if the membrane starts to tilt slightly over the length when cutting, where the more narrow tape has to be exact.
I found no significant difference in baking temperature of 140c vs 150c, so I will probably go with 150c to be on the safe side since the acrylic glue on the self adhesive aluminum can handle the higher temperature.
Also, the 50 um aluminum traced membrane is 0.8 dB more efficient than 30 um, which is not a huge difference. And the distortion is mostly similar but a bit higher in the upper midrange.
In practice, both alu thicknesses work just fine so I might go with the one that is the most convenient based on other reasons. Like if I decide to split the coil and run it on both sides to make the shading network easier, then I'd probably use 2x25 um aluminum.
But if I only do one side the 30 um is easier to cut since my roll is 50 cm wide vs the 50 um alu tape which is 7.5 cm wide. The wider roll can easily handle if the membrane starts to tilt slightly over the length when cutting, where the more narrow tape has to be exact.
Because the baked mylar membranes feel a lot more springy, but still stretchy I decided I wanted to revisit EPDM rubber suspension to see if the mylar can mitigate the weaknesses when using an aluminum composite backed membrane.
And it does, somewhat, but not completely:
As before, the low end distortion is lower, but the top end is a lot more rough. Since I am more interested in a jack of all trades full range membrane than a master in a specific frequency range, I will keep using the foam since it looks to me to be the best overall compromise.
And it does, somewhat, but not completely:
As before, the low end distortion is lower, but the top end is a lot more rough. Since I am more interested in a jack of all trades full range membrane than a master in a specific frequency range, I will keep using the foam since it looks to me to be the best overall compromise.
And to clarify, I didn't use ReMount glue directly on the structural sandiwch support foils, but rather that the residue after peeling it off from the cutting mat was enough to make it stick just enough to the membrane. And little enough glue that it was easy enough to peel away after baking. Also, I guess that the little adhesive also helped to keep the mylar in place during baking to prevent shrinkage.
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although nicely illustrated! i dont get it. you cut your foil attach the mylar (23 true carrier). then add 40 mu al with remount ? problem i have getting that 40 mu of without screwing up the whole foil again, since you bake after corrugation... it screws up the corrugation. ? at least for me. and i dont want to have a sticky membrane 🙂 after all is done. i might miss something there. the problem might lie in the different ways we make foils. i believe you use a cameo as well ?
sorry i dont get it, you made such nice images !!!!
by the way did you read my message ? if you cant get hold of the mylar we can fix something for sure !!
First I cut a coil with border out of 30 um self adhesive aluminum, then attach it to 23 um mylar, such that I get a typical membrane like this:
Then I cut some 40 um aluminum foil and remove the excess. And in this image I have already flipped one of the 40 um cut pieces such that the residue from the ReMount is facing up, then I carefully aligned the membrane and pressed it into the piece with a roller.
The green is the membrane, and the orange dots is the glue residue from the cutting mat.
After placing the second layer of 40 um alu on top to enclose the sandwich, I also decided to fold the top and bottom edges:
And apart from marking with a permanent marker where the extra structural support alu is on the top and bottom, it is ready for corrugation and then baking.
And it didn't take that much force to peel it away after baking. There was some force, but nowhere enough that I was afraid of damaging the membrane.
Perfect get it ! good idea folding the edges 🙂 dont want sticky stuff in your roller !. but you never have the remount sticking to the middle (actual foil)
since i hoped it would come off so easy since it does not like heat but that was not the case. for me ! must admit i needed tpo use 160c since my **** oven goes 160-130 40.... or something (thank god i kept my old oven in the shed so i can try that one , since it is not digital its just playing with it with a probe in there then leave it)
since i hoped it would come off so easy since it does not like heat but that was not the case. for me ! must admit i needed tpo use 160c since my **** oven goes 160-130 40.... or something (thank god i kept my old oven in the shed so i can try that one , since it is not digital its just playing with it with a probe in there then leave it)