Microphone diaphragm tensioning set-up & diaphragm sources?

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gentlevoice1

Well-known member
Joined
Jan 14, 2008
Messages
141
Location
Aarhus, Denmark
Hello,

I'm currently in the process of evaluating various microphone options (as some of you may know) & to that end recently heard about Stephen Paul Microphones in California (thanks to Tim Campbell for this. Their website is not comprehensive but is http://www.spaudio.com/).

It is inspiring to learn that they use e.g. 0.9, 1.5 & 3.0 umeter thickness membranes  8) I have also been reading a bit (to the extent that I understand it  ???) in AIP's "Handbook of Condenser Microphones" and note that a capsule's main resonance frequency depends e.g. on the tensioning of the membrane. On page 43 there's a value given of 2000N/m for a typical 1 inch microphone.

My question is what 2000N/m corresponds to in practical terms? E.g. let's say that I hang a:  1 umeter thick membrane - 10 mm wide - at the top tied to my kitchen table and drawn towards the floor with a weight at the other end: How much weight do I have to add to the bottom end of the membrane to get 2000N/m? Is there a - preferably simple - formula for calculating this?

Also, I have some 0.9 umeter membrane that I'd like to add a thin gold layer on top of so that I can use it as a membrane. Any of you have tried this and have tips on a feasible way to do it? Or maybe one of you know of a source of superb & thin (1-2 umeter) microphone membrane material (with gold)?

Thanks for reading & maybe replying :)

Jesper
 
Wow,
Let me warn you, the rabbits hole you are about to go down is very deep my friend!
That being said getting gold on to Mylar isn't a trivial process. Doing it yourself id out of the question unless you want to spend a boat load of money on complicated equipment.
The process is basically evaporating gold in a vacuum.  The vacuum is really hi and requires specialized pumps, and evaporating the gold in the vacuum is very tricky. Do a google search for
thermal evaporation or thin film coating. You will find company's that specialize in the process.
Also its my opinion that anything less than 3 micron is pretty silly.most not all modern capsules use six micron Mylar.
Eric
 
My question is what 2000N/m corresponds to in practical terms? E.g. let's say that I hang a:  1 umeter thick membrane - 10 mm wide - at the top tied to my kitchen table and drawn towards the floor with a weight at the other end: How much weight do I have to add to the bottom end of the membrane to get 2000N/m? Is there a - preferably simple - formula for calculating this?

N/M  is Newton per Meter is a ratio of Force on surface wich is coresspond in a pressure data , 

if you follow or Newton Friend Equation F=ma  //// Force = Mass * Acceleration ,  you can determine a certain weight disposed on a 1M surface to do the calculation,  this is some not so hard funny Mathematics,

Cheers ,

Dan the Chemist Man,

Dany,

 
 
Here are some pictures of me actually getting some mylar coated.

http://www.groupdiy.com/index.php?topic=48030.msg620306#msg620306

Eric
 
http://www.10000cows.com/DiaphragmTensioning.htm The 120 or 60gm is distributed around the circumference of the capsule to give the tension.

http://www.10000cows.com/deposition_system.htm Les Watts at MicBuilders gave a fuller explanation in a recent series of posts.

While I have a lot of respect for Mr. Paul's work, the idea of extra thin diaphragm material will have most genuine mike designers ROTFL.  especially if you want 2kN/m

There are Links in MicBuilders to suppliers of Aluminium flashed Mylar.  I used that at Calrec.
 
@tskguy: Hmmm... I appreciate your consideration in warning me about what I may potentially be going into  ;) As it is I'd right now rather NOT have to coat a membrane, on the other hand I do have a favorable "inclination" towards very thin membranes (gold coated), so from where to I source them?

I'm also thinking that if I make the microphone capsule myself (or at least mount the membrane) it is of less importance to me if it doesn't last more than a year or so ... Making things for a more or less personal use (adding the musicians as well) allows for solutions that may work outstandingly (sound-wise), yet for sure could not be sold  8)

I'm currently investigating various microphone solutions, and in the first round - to start up recording - I'd prefer to not make the microphone capsule myself, but it is most likely that in time I will venture into this field. To that end - when I do so is it then possible that I can pay you to coat some membranes for me - should that be necessary? Or maybe you know of a vendor that sells 0.9 or 1.5 umeter membranes will a gold coating?

@ricardo: Hi again ;-) Very interesting links you have attached - the diaphragm tensioning method seems very simple indeed ... Yet, since I'm also in the process of building an electrostatic headphone I've decided to go for a tensioning rig similar to this:

http://www.diyaudio.com/forums/headphone-systems/132573-has-anybody-made-els-headphone-6.html#post1826010

As I see it this rig will give me quite good control of the tensioning force while testing e.g. for the capsule's resonance frequency. But I still need to know how to calculate the tension of the membrane (see also below).

Thanks also for your reference to Micbuilders & aluminium flashed mylar. For various reasons, though, aluminium is not a material I would use (I'm not sure I can explain this, Ricardo - might I ask you to just indulge me on this ...) but if you know of a source of gold coated 0.9 or 1.5 umeter membrane then I'd be interested ...

BTW - I looked up ROTFL on the internet & without getting into specifics about Stephen Paul's work it sounds very attractive for me to roll on the floor laughing ;-) Don't know if you've heard about the international laughter movement? It was started by an Indian medical doctor & some years ago spread to Denmark (where I live) and I used to go there & occasionally still go there. It's about laughing  ;D for no reason whatsoever - or for good reasons and to me it's really fun & releasing to let go of being a grown-up (or other "have to be's") and just do - apparently - silly things that make 20-30 people laugh freely together ...  ;)

@poctop: I'll try to do some calculations but Newton's law doesn't take into account the thickness, width or other parameters of the membrane. Shouldn't they be somehow be included?

Best regards to you all ;-)

Jesper
 
Good luck finding any material that thin already coated in gold. It was hard enough finding 6 micrometer material! most places either sell it in to small a quantity for to much money or the want to sell you a thousand pound roll!! And yes a thousand pound roll at 3 feet wide can travel to the moon. Way more than I will ever need. So here is the deal on me coating something for you. Its a huge pain in the ass and just the cost to run the machine is 600 dollars you then need to purchase 2 troy ounce of pure gold, it only uses around a gram but they need the amount for the process. You also need to have the masks made acording to what you desire. My needs were 23mm round targets of gold. that explains my funky rig in the pictures. They are also close to me so I drove to the facility and waited for them to coat the mylar and then I took the finished material with me. So for me to do this for you would require exrtra payment for my time as well as getting it prepared for shipping. I would highly recommend searching for a local company like I did that is willing to work with you to give you exactly what you want. I did see some mylar that thin during my hours of searching but I have no idea where. And it wasnt coated.
 
gentlevoice1 said:
http://www.diyaudio.com/forums/headphone-systems/132573-has-anybody-made-els-headphone-6.html#post1826010

As I see it this rig will give me quite good control of the tensioning force while testing e.g. for the capsule's resonance frequency. But I still need to know how to calculate the tension of the membrane (see also below).
This is a terrible way to tension a diaphragm.  It is no way consistent enough for a microphone.  I think you will find that practically all mike makers including the big Germans and Harman use a similar method to Dale.  I used this method at Calrec for the Soundfields.  The same jig tested resonance, capacitance and collapse voltage.

The important factor isn't tension but the resonance.  There's a good PDF book on microphone design on the Neumann website.  It's the ONLY accurate and useful text on mike design I've found.  Link to it in MicBuilders.

For various reasons, though, aluminium is not a material I would use (I'm not sure I can explain this, Ricardo - might I ask you to just indulge me on this ...) but if you know of a source of gold coated 0.9 or 1.5 umeter membrane then I'd be interested ...
Before you sneer at Aluminium, you need to look up Les Watt's posts on Gold Flashing in MicBuilders.  He'll probably sell you a small quantity but it might be as expensive as tskguy.  Josephson or Peluso may also sell you some.

Don't buy any Gold flashed stuff that doesn't come already stretched & mounted or isn't made by a reputable mike maker.  Again see Les Watts.

I'm assuming you want to make something which works and sounds good.  If not, just ignore anything I say.

Oh!  And good luck on finding 0.9um material.
 
in AIP's "Handbook of Condenser Microphones" and note that a capsule's main resonance frequency depends e.g. on the tensioning of the membrane. On page 43 there's a value given of 2000N/m for a typical 1 inch microphone.
gentlevoice, Can you scan page 43 and some of the pages around there and post?  2000N/m sounds very high.  You certainly can't do that with 0.9um Mylar.
 
@ricardo: Yes, I'll do some scannings (or photographies) of p. 43 and adjacent pages (I'll send you a PM). However, in the meantime can you help with a formula on how I calculate the tensioning of the membrane? It can't just be hanging ~200 kilos of weight at the bottom of the membrane (somehow must relate to cross-sectional area & maybe more of the membrane) ...

And, yes, if I go into microphone building, it'll be to make something that is extraordinary (to my senses). So I am very interested in solid information about this - also as preliminaries in evaluating whether or not to enter this field. About Micbuilders, I joined the group, but immediately got many mails about various topics which is less feasible to me. I'd rather join in when I'm so inclined. Do you know if I can be a member yet not receive these mails?

About the membrane tensioning device I think that what Philippe Hiraga (of past L'Audiophile) did was to mount rollers inside the box with weights distributed on a wire that went from roller to roller. The rollers were then at the other end of the clamps that are attached to the membrane. In this way he insured (as I remember understanding it that) all clamp points had an identical tensioning. Could that work?

Thanks for suggesting Josephson & Peluso for membranes ;-) (Do they also sell this thin membranes?)

@tskguy: .... Sounds expensive :-( As it is I actually have meters of 0.9um membrane so that may be solved. A source is:

https://www.a2zcorp.us/store/category.asp?Cguid={09226D2B-50FF-40F8-9EA2-DC9CA9D6ADD4}&Category=BuildingMaterials:Covering

- the top right and left products. I can also send you some if you are interested ...

Yet I need a way of coating it. I've considered putting some gold leaf on the membrane - I have some that I have measured to be ~ 0.04 umeter thin (amazing that it can be so thin!) and I'm considering ways of putting in on the membrane ... But could I find some already made membrane that might just be easier ...

Thank you both for replying ...

Best for your day - wherever you may be ;-)

Jesper



 
gentlevoice1 said:
About the membrane tensioning device I think that what Philippe Hiraga (of past L'Audiophile) did was to mount rollers inside the box with weights distributed on a wire that went from roller to roller. The rollers were then at the other end of the clamps that are attached to the membrane. In this way he insured (as I remember understanding it that) all clamp points had an identical tensioning. Could that work?
No.

Thanks for suggesting Josephson & Peluso for membranes ;-) (Do they also sell this thin membranes?)
No.

https://www.a2zcorp.us/store/category.asp?Cguid={09226D2B-50FF-40F8-9EA2-DC9CA9D6ADD4}&Category=BuildingMaterials:Covering
Yet I need a way of coating it. I've considered putting some gold leaf on the membrane - I have some that I have measured to be ~ 0.04 umeter thin (amazing that it can be so thin!) and I'm considering ways of putting in on the membrane
It will fall off.

Why don't you try Aluminium coated Mylar?  This is MUCH easier to handle. There is no performance difference unless you use too heavy a Gold layer like Gold Leaf.  Once you get your capsule going, you can start looking for Gold flashed stuff.

Your questions tell me you haven't bothered to read Les Watts on Gold coating.

Also have a look at Debenham, Robinson & Stebbings.  There is a link on MicBuilders in Files.  Bernhard Weingartner, who designed the C12 for AKG, says good things of it.  It is also suitable for 0.9um film though there is no advantage except Golden Pinnae cred.

You need to build something which works and preferably sounds good before you plan your ultimate mike.  This means following a good known design exactly.
 
Your questions tell me you haven't bothered to read Les Watts on Gold coating.

Just briefly now as I'm underways to something else ... I can't get into Micbuilders right now as I happened to make an unsubscribe to Micbuilders instead of only to the emails. So will have to sign up again.

Greetings,

Jesper
 
@Ricardo: I signed up to Micbuilders again and have read up a bit on the names and suggestions you gave me, and also on what you wrote in the last post. For now I'll have to ponder what to do next and in which direction to move ... I've sent you a PM with the photographs of the pages close to p. 43 in the AIP book.

... Yet to briefly revert to my OP question, I'd appreciate if one of you have a formula on how to calculate the tensioning of a membrane in N/m based on the membrane's thickness and other relevant parameters ...

Best regards,

Jesper
 
gentlevoice1 said:
I've sent you a PM with the photographs of the pages close to p. 43 in the AIP book.
Thanks for this Jesper.  Table 3.1 describes a 1" omni like B&K4145.  The diaphragm has 8900kg/m3 density; ie its solid Nickel.  That's why 2000N/m is no problem.

I'd appreciate if one of you have a formula on how to calculate the tensioning of a membrane in N/m based on the membrane's thickness and other relevant parameters ...
On Dale's Diaphragm Tensioning rig, when you place the ring with the diaphragm over the capsule, the diaphragm will form a small angle between where its clamped to the edge of the ring to the capsule rim and the horizontal, eg A radians.

Divide the weight of the ring by Cos(A) to transfer it to the Diaphragm Tension.  Divide by the circumference of the ring clamp and you have your N/m.

Divide that by thickness to get stress in your material which must not exceed the plastic limit.

I would use a much larger clamp diameter for more even tension.  This is vital as Dale says.

His capsules have a resonance around 800Hz.  For a good omni, you need to raise that to at least 10kHz.  MUCH more tension (and material stress) required.  0.9um Mylar may be ju..ust OK for him but will stretch beyond the plastic limit for you.

You need to stretch the diaphragm on the tension rig clamping ring to about the right tension before you deposit Gold or it will crack.  Aluminium can be pre-coated before mounting on the clamping ring.
 

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