Microphone membrane.

Hi diy'ers,

I hope one of you may be able to help with a tip on where to find this in not too large amounts:

As it is I'm looking for a source of very thin membranes preferably coated with a thin gold layer. Membrane thickness preferably between ? - 2 umeters and then as thin a gold layer as practically possible while considering good and stable conductivity also in the long run. The membrane will not be bent. Sizes should be a minimum of 20*20 cm (for a headphone).

The membrane is not to work under much tension so long-term mechanical stability under tension is not important.

For a start it may also be a membrane covered with e.g. aluminum but gold/a gold alloy is preferred.

Also, in this context, if one of you knows of a not-too-complex "paper" or link describing the qualities of various membrane materials' I'd be pleased to hear about this as well.

I'd appreciate any links/connections you may be able to share 

Cheers, Jesper

More info needed:

How much conductivity do you estimate you really need?

Some of the thin-sputtered films that I have seen measured in the range of 50-100 Ohms per cm (!)

In condenser microphones this is not a problem, but if you're planning to send in any significant current, it may obstruct operation.

Jakob E.

Hi Jakob 

Thanks for your quick reply and relevant questions ... And, yes, I should specify the approximate conductivity needed as some current - albeit in the mA range - will be sent through the membrane. Will need to calculate and hopefully will get back later today.

Jesper

So I have some experience getting thin films coated with gold for my capsules. I actually have 6 micron sheets coated with gold for my CK12 capsules.  The only film that's practical for this application in the states is Mylar. You can get it all the way to 1.6micron thin but its a son of a gun to work with!  6 micron is my choice for capsules but I'm not sure what you would need for some electrostatic headphones. I would think 6 micron would work just fine. Now getting even uncoated Mylar in quantity is a big challenge and then getting coated is small batches is a bit cost prohibitive.  This is a big reason why you don't see a large number of guys building capsules!!  Please contact me privately and we can discuss further if you like.

Eric

Hi Eric,

& thanks for your reply 

As it is I'm actually not doing an electrostatic headphone but will be using magnets - so the tensioning of the membrane just needs to be sufficient to keep the membrane free of the magnet assembly. And with this in mind I'd like to go with as thin a membrane as possible. I already have some 0.9 um membrane which is utterly, utterly light (it almost flies ;-)) and it is tricky to work with but I intend to make a tensioning device to make this feasible. I'm pretty confident it should be possible even to remove some of the gold to make the tracks.

However, the 0.9 um membrane is not yet covered and it really would be a magnificent help if you or another of the diys have access to such equipment (the cost is a bit high to have it made the business way) ... FYI I'm taking some days off now (weekend +) so I won't reply (or send you a PM) before probably some time in the middle of next week.

Best wishes from over here 

Jesper

I don't think that ultra-light membrane material will do any real difference in a magneto-dynamic setup: Significant current is the only thing that will generate a strong-enough magnetic field to move anything.

Try to estimate the mass of the needed conductive material (length x area) - my intuition tells me that you will end up with MUCH heavier coil than membrane, no matter how you choose conductive materials for it..

Extremity: Maybe with carbon nanotube for conductor (what is conductivity - and availability)? Laminated between two layers of polyethylene or HDPE?

I worked with this type of headphone in da previous Millenium.

Max. sensitivity & other good stuff is when the mass of the conductor is roughly equal to the other masses.  The most significant of the other masses is the air load.  Diaphragm material is almost inconsequential.

What IS significant is the conductor material.  Aluminium is BY FAR the best in this regard cos its high conductivity and low density. 

Hi all,

So I'm back after a longish audio "weekend" ... Thanks for your many replies which I've been pondering for the last couple of days. As it is I have decided to go with what is readily available in the first round - just to get started.

So in case one of you know of a source/vendor for mylar/other + aluminum membrane I'd really appreciate to hear about it/get a link. (Width must be no less than 15 cms. Aluminum thickness no more than 1um and no less than 0.2 um).

Somehow my intuition stills tells me that - for my audio preferences - a thin membrane is preferred ("0" - to 2 um incl. aluminum) so if this is somehow available that may also do for a membrane to actually be used in a more finalized design ...

I'd also be very interested in a link to a low-volume vendor that sells e.g. polypropylene or polyethylene films in ultra-low thicknesses possibly coated with either a thin gold or aluminum layer - or someone who can thinly coat a membrane with aluminum, copper, silver and/or gold. 

BTW mylar's density is 1.39 g/cm3 and aluminum's is 2.7 g/cm3 whereas gold's is 19.32 g/cm3. So the balance between mylar/aluminum should be less decisive, whereas gold (if for no other reason then price-wise  ) needs be a thin layer.

@gyraf: The laminated membrane you mention is a very interesting suggestion - I've actually considered it myself also as a possible means of reducing distortions in the membrane. Maybe for a future investigation?

@tskguy: Now I don't know if you are interested in very thin membranes but I just found some 0.5 um mylar on ebay. I can send you a link if you are interested?

@ricardo: Thanks also for your feedback ... It makes me think that I would like to know more about the physics of this so might you have a link to a not-too-complex article/source that describes this:

Max. sensitivity & other good stuff is when the mass of the conductor is roughly equal to the other masses.  The most significant of the other masses is the air load.  Diaphragm material is almost inconsequential.

Click to expand...

Best wishes & thanks for any feedback you may be able to give 

Jesper

> 20*20 cm (for a headphone).

20cm is, what, 8 inches? My dogs' ears are not that long!

> the air load.

Right. For lows, there is a mass of air which moves with the diaphragm, and may be approximated as a hemisphere with base the area of the diaphragm. Light paper loudspeakers may have as much mass in this air as in the paper! For highs the moving air only extends maybe a half-wavelength, so about an inch thick at the top of the audio band. I don't have density of air at hand, but I bet this is far more than your micron of Mylar. That you could go 2, 4, even 10 micron without much effect. But much more local stiffness and less trouble from local resonances.

Now the conductor.

Gold is dumb. Its conductivity is similar to Aluminum, but (as you say) it is SEVEN times as dense as Al. Sensitivity will be a lot about conductivity per pound.... at higher frequencies your weight is your main problem, at any freq Ohms are a drag, you want lowest Ohms/Pound. Lithium is good except it burns on contact with air. Aluminum is next, and THE metal for tweeter voice-coils. Copper is not much worse, generally used in speakers which do not want to fight Al's poor solderability for a few dB more treble. Gold is much worse. And mass generally appears as M^2, so 7X mass is 47X less output.

I have other frets. All the topologies for planar dynamic have either poor magnetic paths or poor conductor paths. Yes, the super-energy magnets now allow ideas we could not tolerate in the old days.

> mass of the conductor is roughly equal to the other masses.  The most significant of the other masses is the air load.

ricardo is not as stupid as he sounds. All engineering comes to problems of proportions.

Sometimes one factor is "cheap". When we run electric power, it is affordable to make wire-loss very small. We do not "match". Wire loss is like 2%-5% of total power. A 1 Ohm circuit feeds 100 Ohm lamps.

But in dynamic speaker, we need conductor (to get much energy through the electric side), we need area (to paddle a lot of air), and this means we have Air-Mass. We may generally make all three factors roughly equal. JBL E130 speaker has about 20g of Al, 15g of paper, and faces about 30g of air-mass. Speakers with 100g of coil+cone exist but are deliberately VERY low efficiency. (They want to depress midrange to match the small bass of a too-small cone.)

So estimate your air-mass. Plan total diaphragm similar. Decide how you split that budget between Al and Mylar.

In the E130, the conductor (coil) is a lousy diaphragm, so it needs big paper. In your construction you want to make the most of your magnetic field, so your Al will be spread-out and give some diaphragm action. But a solid leaf would have embarrassingly low resistance (and audio impedance), also poor use of mag field, so your conductor will be many ribbons. So you need some Mylar to tie it together.

I do think you should be looking at Al foil. That you'll never sputter enough Al onto Mylar to get any real power into the system.

My estimates of air-mass are for a circular diaphragm without obstruction. I bet you'll have a lot of iron in the air path. This will add some resistance to the acoustic impedance, maybe some inductance, but no free lunch. Moving air IS moving mass, and sticking objects in the way doesn't make it easier.

(One exception. Instead of a large diaphragm, a small loudspeaker can lever large air area with a horn. In a good horn the mass is masked by up-levered acoustic resistance, useful loading. But over the audio band a horn must be HUGE, and I don't see a broadband application to something that sits entirely on the head.)

Hi PRR,

Hmmm ... "long time no hear" but once more I appreciate your input. I'll keep your more theoretical considerations in mind when moving onwards - very understandable to me - so thanks 

20cm is, what, 8 inches? My dogs' ears are not that long!

Click to expand...

SMILE ... weeeelll, it's because I would also like some length/width to fasten the membrane to the tensioning device ... But could be quite interesting e.g. to answer someone knocking on my front door with a couple of small loudspeakers on each side of my head  :

However, as it is it seems that the practical aspects of getting membrane materials is the most challenging. I contacted Mundorf (capacitors, coils etc.) the other day and they actually were as helpful as to offer me some of their capacitor film - but the width was a maximum of 48 mm. I will be contacting other capacitor manufacturers but somehow need "THE" hint that puts me in a useful direction. Like a link to a vendor/manufacturer that sells membranes to e.g. microphone manufacturers in small amounts ... I've also contacted Thiersch microphones & Mr. Thiersch was also very open to helping me with some membrane material, however, not available in these sizes.

Aluminum foil I also can't seem to find in these thicknesses.

So that's where it is right now ... Interesting that often finding the materials/components can take so much time ...

Yet, thanks once more PRR - & best wishes from over here ...

Jesper

gentlevoice1 said:

I contacted Mundorf (capacitors, coils etc.) the other day and they actually were as helpful as to offer me some of their capacitor film - but the width was a maximum of 48 mm. I will be contacting other capacitor manufacturers but somehow need "THE" hint that puts me in a useful direction. Like a link to a vendor/manufacturer that sells membranes to e.g. microphone manufacturers in small amounts ... I've also contacted Thiersch microphones & Mr. Thiersch was also very open to helping me with some membrane material, however, not available in these sizes.

Aluminum foil I also can't seem to find in these thicknesses.

Click to expand...

The aluminium on Capacitor film is far too thin to be of use in practical headphones.

The ideal is Mass of Aluminium equal to Air Mass.  The diaphragm & other mass should be inconsequential in a good design.

On the Wharfedale/LEAK Isodynamic headphones, we used flexible PCB material, Cu or Al on Kapton.  You also need to dream up some way to get as much length of conductor in your magnetic field.  The force generated by an electrodynamic transducer (your Isodynamic headphone) is F = B l i
B: flux
l : length of conductor
i : current

Look at other 'ribbon' headphones to see what they use.

Buy a copy of 'High Performance Loudspeakers' - Martin Colloms.  Can't remember if it has a chapter on headphones but the rest is useful & pertinent info  ..  especially the stuff on treble units.

But there's no good book that's as accurate & useful on speaker design ... like the Neumann book on Microphones.

Hi all,

So now it seems I have been really!!! lucky (gifted  ). This morning I called a company close to where I live where they do vacuum metallizations and asked if he could help with metallizing some membrane material. And, yes, he could - if I just brought and picked up the material he could metallize my membrane as part of what they otherwise do  ;D Some help indeed!

So I've been doing some calculations on which resistance I'd end up with various thicknesses and widths of aluminum as the conductor material. And although I've checked my calculations several times, based on your comments here about thicknesses of relevant materials, I wonder if there's a mistake somewhere ?? So I hope one of you will comment if it's incorrect ...

Aluminium specific resistivity (called @):  2.82 * E-8 (Wikipedia data)

Resistance of a given conductor:    R=  @ * length/cross section area

So assuming that the conductor's data is:

Conductor width:  5 mm

Conductor thickness:  1 um (1*E-6)

Conductor length:  1 meter

... then I get the resistance of this conductor to be 5.64 ohms. Would this be right (should be ...)?


@ricardo: Thanks for your comments & suggestions. Reading your post made me remember that I saw your force formula during high school time - interesting how such "old" information sometimes remains valid ...

Look at other 'ribbon' headphones to see what they use.

Click to expand...

  .... thanks for the tip ... I already am 

Cheers,

Jesper

Hi again,

... found a link to some metallized mylar in another thread here at groupdiy:

http://groupdiy.com/index.php?topic=57782.0  (post #3)

So will try out things with this membrane and some other mylar I am getting.

Cheers,

Jesper