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Metalized Mylar/BoPET for planar driver

post #1 of 10
Thread Starter 

I've had an idea for a while of building a set of planar magnetic headphones, completely from scratch, partly to see if I can make something good but mostly for the fun of it. One thing that is really holding me up is finding the things I would need - in particular reasonably thin metalized mylar. The best I've been able to find that is sold in small quantities is 2 inch wide, 2.5mm (~1/10inch) thick tape, but based mostly on looking at plastic films that thick, I expect it would make a terrible diaphragm.


Does anyone know where I could find a very thin sheet of metalized mylar? preferably in NZ or Australia, but if it's good and has a good price I'd be prepared to import.


Also, I don't really know too much about the etching process. From what I understand standard process would be to mask out what you want to keep, then imerse in an etchant (I've heard that the standard is 0.1mol/L FeCl3(aq)). Would this work? What could I use as a mask? Is there anything else I should know about etching (besides standard lab safety for handeling chemicals)?


If what I want can't be had, what other options are there?

I don't want to go half-assed on this project, so I'd rather not go with things like gluing Al foil to cling film, unless that actually makes a good diaphragm. Basically when I'm finished I either want a good set of headphones, or I want to know that they sound bad because my design/build was bad. I don't want to be left thinking that I could have made something good if I hadn't cheaped out on materials, although at the same time I am by no means able to spend stupid amounts on this.


Thanks in advance for your response.

post #2 of 10
If I were you, I would just buy the drivers. Most of your effort should go into making the cups of the headphones, and the over all engineering and design. The drivers generally speaking aren't that expensive, and you can base your general headphone design off of an already well know pair of headphones.
post #3 of 10
Thread Starter 

From the point of view of getting a finished product I would agree with you, but for me this is much more about the process of building and designing than getting a set of nice headphones at the end. Sure, I do want a good set of headphones, however I want to create the whole thing, not just assemble a kit, so to speak.

Thanks for your input.

post #4 of 10

Hey Salmon,


I'm also playing around with etching and such. I want to make planars and AMTs. You can get metallized film out of capacitors, that's one of the things that it is used for. I have some in front of me about an inch wide. Two of these side by side would be a good size. Otherwise look on ebay. 3m sell the metallized film tape. I'm not sure yet how many microns is ideal. Efficiency needn't be high in headphones.

post #5 of 10
Thread Starter 

Hi Symphonic,


Thanks for the advice. I will look into capacitors, although I have managed to find some 2µm and 4µm alumized mylar film from a model plane site. Wont post it here, but if anyone wants pretty cheap alumized or clear 2/4µm mylar PM me and I'll link to it. From looking through the DIY Electrostat thread they seem to go for somewhere between 1.5 and 6 µm, so if I can afford the custom magnets I need I'm likely to get 2µm AL mylar from this store. The only issue I can forsee is having a sheet resistance thats too high for my purposes.

On the topic of etching, I've done more research into this. Aparantly, due to AL being amphoteric, standard etchants are strong acids or bases. Because of this I would go for diluted NaOH from a hardware store, but that could cause problems of its own, as ester bonds are attacked by both acids and bases.

I'd be much obliged if someone who knows more about chemistry/etching than me could suggest an alternative that wont attack the mylar, and is reasonably easy to obtain, or convince me that dilute NaOH wont damage the diaphragm.


Once again, thanks in advance for any help.

post #6 of 10

I missed your reply.


I've also been playing with etching Al and have tried NaOH already. It works and the mylar was left intact but it killed the permanent marker that I wanted to use for the masking.


Check out another thread at DIYaudio entitled 'DIY AMT" or something like that, I am SEdwards there. Another poster mentioned a solution based off of copper sulphate and table salt that is gentler for etching Al. Electrolysis also works (tried that) though I'm not sure if it will leave little islands.


As for traces, I just discovered (yesterday) that IDE cables are an excellent tool for this. The wires are about 1mm apart and the gap between them makes for a nice relief for the pen to fit in.


Magnet wise, the Fostex T50rp have 30 mm x 4 x 2 magnets. I think that this is a good width/depth to copy. Length it is up for grabs. 3 magnets per column is enough. I think that Audeze overdo it.

post #7 of 10
Thread Starter 

From what you've said here I think I might go with NaOH. What concentration did you use? And do youu know any other easy to use masks that work with NaOH?


Thanks for the thread. I'll read through to see if there's anything useful. You mention copper sulphate - any idea as to where to get this?


Not sure that I understand what you mean by using IDE cables for traces. Could you explain what you mean?


As for magnets, I'm going to sound nuts but I'm planing on using a completely different magnet array to the standard (eg T50rp). I'm planing on building a K=2 Halbach cylinder, mounting the diaphragm inside the cylinder, and etching several parallel traces, looped back round using copper wire. Before anyone says, 'Thats a bad idea, just go with the standard method.' I'm more than aware that it could go badly wrong, but the idea will forever be going through my head (as it has been for the last year and a half) unless I try it. It could fail, meaning I can put it to rest, or it could work, meaning my strange idea was actually a good one. Either way I want to try.

post #8 of 10

Ok, that magnetic circuit looks very cool. :D I hope it works out. I suppose you can do a simple planar with the standard push pull at the same time so that the longer R&D time with the alternate circuit is not so painful.


To test NaOH I just put some of the granules from drain cleaner in a jar and added warm water and the Al. Just rough experiments at this point. Nail vanish held up reasonably well to the NaOH but I'm still not 100% convinced.


Copper sulphate can be bought from hardware stores for killing roots I believe.


I'm curious about your source for metalllized film, do tell!


As for the IDE cable, what I mean is that it can be used as a sort of reverse stencil for drawing traces on the film. The well between parallel wires holds the tip of the pen so you don't need to use a ruler. I suppose that you might want to use a printer for the etching, but for testing it is probably easier to hand draw the etch resist. If you have some old hard drive cable laying around you can see what I mean. Place something on the cable and draw lines that go between the individual lines. The tolerance is pretty good.

Edited by symphonic - 12/18/12 at 11:37pm
post #9 of 10
Thread Starter 

I'll just post the link to the mylar. Mods, if this counts as spam then sorry, just trying to help out a fellow DIYer.


2µm and 4µm Al mylar, as well as some similar thicknesses of clear mylar for those intrested in additive etching or electrostatics. The 2µm reportedly weighs 2.6g/m^2.


Found some CuSO4, and learned something new. Apparantly it's sold as fertiliser. Pretty cheap too. Oddly enough my search for CuSO4 in New Zealand came up with a guide on how to etch Al. It's a guide for print makers, not electronics, but there are two good points. Firstly it recomends the etching solution (1L H2O 70gCuSO4 140gNaCl) and makes the point that CuSO4 doesn't etch through Aluminium Oxide, so scratching/scouring the surface gently may be necessary. as for NaOH, I may just experiment a little with CuSO4 first. look to be a solution that wont attack mylar.


At the moment I think I'll just wait for christmas and hope santa brings me some spare cash so I can start getting the things I need to do some experiments.

post #10 of 10

Thanks for the link. No pressure from me to rush along. These labours of love take a bunch of time.


I'll post my experiments here too. I will try electro etching at first since I already have some pens that can stand up to the salt solution.


I'm curious about photo resist methods where you shrink the image from the mask before the light gets to the substrate. This is used in the semiconductor business. I have a magnifying glass....

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