Sorry for being a bore, you are doing such a great job in going to the bottom of things that we all benefit from, but I was thinking:
With more or less the same weight, it seems like the membrane with the 3M film above has an Fs of 200 Hz. So the 3M film is less compliant than the 6 µm.
A heavier membrane means also that greater force is needed to move the pleats, at least for the low frequencies; it is 3 dB slope from Fs and up.
Another way to go is to try to increase the compliance (Cms) of the "hinges".
So perhaps one should try to rub off some of the PET 3M in the bottom of the pleats instead of increasing the weight of the pleats (Mms).
With more or less the same weight, it seems like the membrane with the 3M film above has an Fs of 200 Hz. So the 3M film is less compliant than the 6 µm.
A heavier membrane means also that greater force is needed to move the pleats, at least for the low frequencies; it is 3 dB slope from Fs and up.
Another way to go is to try to increase the compliance (Cms) of the "hinges".
So perhaps one should try to rub off some of the PET 3M in the bottom of the pleats instead of increasing the weight of the pleats (Mms).
Attachments
I have to look at all my latest measurements .
But i like to build!!
My next 2 diaphragms will be 7mm deep 80x 32 double 40my alu.
One with 3m tape and one with 6my pet on oneside and 3m tape on the other .No need to remove glue.
The length of a double conductor 80mm is 4,5meters.
Resistance of the 8mm deep double is 1,4 ohm.
Bernt
But i like to build!!
My next 2 diaphragms will be 7mm deep 80x 32 double 40my alu.
One with 3m tape and one with 6my pet on oneside and 3m tape on the other .No need to remove glue.
The length of a double conductor 80mm is 4,5meters.
Resistance of the 8mm deep double is 1,4 ohm.
Bernt
Plenty of time to do that later!
Yes, you a definitely in the flow right now!
Keep'em coming!
I found some aluminium square tube 100x40mm 4mm thick walls, as i was shopping for my carport.
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Suits my 80mm models.
Diaphragm is 40my alu 3m tape and 6my mylar.Lack of bass
Listened to the 40my alu 3m tape 80x32x7mm. Sounds better than the above.
Measures later.
Bernt
Suits my 80mm models.
Diaphragm is 40my alu 3m tape and 6my mylar.Lack of bass
Listened to the 40my alu 3m tape 80x32x7mm. Sounds better than the above.
Measures later.
Bernt
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Above 40my alu 3m tape and 6my mylar 80x32x7mm measured at 20cm dist .off axis
40my alu 3m tape 80x32x7mm 20cm dist. off axis.
Bernt
I will try with 10my mylar 40my alu.
And 12my mylar 40my alu.
Where can i get it.
Cant find it on ebay.
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Nice work Bernt !!! you are on the roll!!, wich i could cut these tubes nice and square
dont have such nice metal equipment. there the freeflight sites comes by again
hehe we all find the same sites one day or anotherhe is pretty fast and expensive i must add but all comes well packed.
so it seems that thicker alu and thicker mylar results in lower resonance. and what Solhaga mentioned is true as well, it will lower SPL. but if you are int he region of 100db already i dont think that is a major issue
Hi Bernt,
What is the ratio of your width by depth for the pleats of your diaphragm ? As far as I know from the Heil's patents, it seems that a ratio of 10 is good and... sufficient. But have you experimented on this point ?
Do you have an idea of the "Bl" of your AMTs ? In other words, do you estimated the force underwent by the Mylar sheet ? What are the currents involved in the aluminum strips, more or less ?
Thank you for any info.
What is the ratio of your width by depth for the pleats of your diaphragm ? As far as I know from the Heil's patents, it seems that a ratio of 10 is good and... sufficient. But have you experimented on this point ?
Do you have an idea of the "Bl" of your AMTs ? In other words, do you estimated the force underwent by the Mylar sheet ? What are the currents involved in the aluminum strips, more or less ?
Thank you for any info.
I have used the same tool for almost all of my diaphragms.
It is build with 1mm alu plates. It gives 1mm width.
I have tried different depth's From 5-10mm.
My ESS diaphragm is 4mm deep and app.1mm wide pleats.
I have not looked at BL.
Before measuring I use to connect to DC. with a automatic fuse at 2 amp.
Using a variable transformer I turn it up until it cuts off.
At normal audio use it is less than 2 amp.
I can measure it, if you want it.
Bernt
It is build with 1mm alu plates. It gives 1mm width.
I have tried different depth's From 5-10mm.
My ESS diaphragm is 4mm deep and app.1mm wide pleats.
I have not looked at BL.
Before measuring I use to connect to DC. with a automatic fuse at 2 amp.
Using a variable transformer I turn it up until it cuts off.
At normal audio use it is less than 2 amp.
I can measure it, if you want it.
Bernt
I have had opportunity to look at AMT diaphragms being fed 30 hertz up to 30 watts under a 300 times microscope.
I did not see any movement. Believe me I tried. Then a colleague of mine tried. Again nothing is visible.
They do indeed work. But they are a very strange beast to try and model, let alone quantify how they work.
I honestly expected to be able to see some kind og flex in the diaphragm. But none was evident.
I have another idea to try as it may indeed be the answer.
If I get anywhere with it I will let you guys know.
Solhaga has filmed movement herehttp://www.diyaudio.com/forums/planars-exotics/232634-yet-another-diy-amt-67.html#post4561575
And I see movement as well on my latest models.
Bernt
And I see movement as well on my latest models.
Bernt
Thanks!
DC, ramped up in voltage.
But still movement.
Interesting.
I read a couple of things I noticed that I may be able to help with.
I have researched most available commercial AMT's. The only one that uses Kapton is the Mundorf. And it has the highest distortion.
Almost all the other use polyester. They tint the polyester yellow. Kapton is brown to light brown. Not yellow.
I did fabricate a diaphragm out of Kapton and Copper.
It did not sound very good. And not very efficient.
One other bit of interesting information.
Arum Cantus make a very nice sounding AMT. They say it is made of Aluminum.
Again I have worked with it and analysed it.
It is not aluminum.
Small hint is that it is magnetic.
As far as as I have experienced aluminum is not magnetic!
Thanks for mwmkravchenko your insights. They are of great value for the AMT DIY:ers 
.
I also filmed an AMT at 150 Hz, but perhaps you saw that one as well.
My conclusion on the AMT-movements and the distortion made by their lack of linearity and also the low frequency cut-off, is that one has the work with the Cms. It is by far too low and irregular.
I have some ideas, but I'll take them later in my thread.
Thanks again, Bernt for the passionate work you are doing (for us).
It's a gold mine of research. We all love you for that.
BTW:
The Aurus Cantus AMT you'r referring to for sure cannot be this one?
.I also filmed an AMT at 150 Hz, but perhaps you saw that one as well.
My conclusion on the AMT-movements and the distortion made by their lack of linearity and also the low frequency cut-off, is that one has the work with the Cms. It is by far too low and irregular.
I have some ideas, but I'll take them later in my thread.
Thanks again, Bernt for the passionate work you are doing (for us).
It's a gold mine of research. We all love you for that.
BTW:
The Aurus Cantus AMT you'r referring to for sure cannot be this one?
If you take a tweeter which has at least 2. order roll off at say 2 kHz and feed it with 30 Hz ... would you expect to see much movement?
I think the german magazines Klang und Ton, and Hoppy HiFi have presented measurements of all commercial AMTs over the years. As I see it the Mundorfs has the lowest distortion or on par comparing similar sizes. So it is interesting that you have found the opposite. Which brands and models have you compared?
About the capton ... how can you confirm it is not Kapton?
I'm sure it will feel more crisp and stiff, compared to poly.
I think Kapton by upont is quite yellow in color
http://www.dupont.com/products-and-services/membranes-films/polyimide-films.html
Other brands can maybe look a bit more brown
Croylek | CROYFILM KAPTON FILM 500HN
But I guess it also comes down to the thickness.
And of course I might be wrong.
So you took out the diaphragm of the Aurum Cantus and found that it was magnetic? .... interesting info if this is the case.
BR Baldin
hmmm i dont htink they colour polyester to Kapton colour. that would be stupid. i made a few Kapton version and they sound perfectly fine. for me the problems is the glue on my tape witch adds weight. and the fact that Kapton cant be heat set. or at least not on a temperature my jig can handle. the Kapton sounds less crispy more damped. this could be because of the glue on my tape or the Kapton itself.
magnetic ?? that would suggest a sort of metal.. it might be me not getting the reason behind it but with the information i have at this moment i cant believe it has metal in it. weight wise not useful and conductivity is also not the best.
magnetic ?? that would suggest a sort of metal.. it might be me not getting the reason behind it but with the information i have at this moment i cant believe it has metal in it. weight wise not useful and conductivity is also not the best.
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