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Old 8th March 2004, 10:08 AM   #1
OliverD is offline OliverD  Germany
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Cool DIY Air Motion Transformer

The original ESS Air Motion Transformer (see my avatar) has a very smooth and sparkling sound and its resolution is about the best you can buy. Once you've built speakers with them, you wouldn't want to go back. However, a new pair of these drivers costs about 1000 Euro (about the same in US$). Sure, you can look on ebay, but they are still pricey as you are competing with all the other audio fanatics. Plus you never know what you get, as the diaphragms can fail in many subtle ways.

Hence my plan: DIY Air Motion Transformers. As I took one of my old ones apart, I realized there is really nothing special about them. No part that I couldn't replicate in the workshop I have access to. Except for the magnets, and the diaphragm. The ESS diaphragm is available as a replacement part for about 70 US$, so I decided on using the original ones. The magnets (you need 4 of them per driver) are about 125mm x 50mm x 18mm in size and I don't know any further specs.

I think I will give it a try. In case anybody is interested joining in, what I need to figure out is a way of getting / measuring the magnet's specs (material, force factor) and a cheap source, preferrably in Germany, for buying them.
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Old 8th March 2004, 11:24 AM   #2
sreten is offline sreten  United Kingdom
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http://www.indigo.com/magnets/ferrite-magnets.html

One way of approaching the problem is to assume fairly standard
ferrite material, and build up the magnets from a large number of
smaller magnets.
I think you would also need some special magnetically loaded
adhesive / epoxy but no idea where to source this.

You need the type that are magnetised through the thickness.

sreten.
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Old 8th March 2004, 12:05 PM   #3
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Speaker Builder had an article on building an AMT in the 1982 volume. It was a front radiating, rather than bipolar design that the author mated to a home made horn. The AMT build cost him about $550 back then.

back ussues available for $18 at http://www.audioxpress.com/magsdirx/...r/sbbilist.htm
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Old 8th March 2004, 12:33 PM   #4
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Instead of "boring" ferrite magnets you could also use Neodymium like:

http://www.torcman.de/shop/index.html?magnete.htm

or

http://www.supermagnete.ch/magnets.php?at=Q


Regards

Charles
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Old 8th March 2004, 07:31 PM   #5
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I use the AMT 1A and cant do without, so iŽd like to build my own too.
Will go for making diaphragms also. Magnets are pretty basic ferit material, assemble from smaler standard blocks is ok, iŽll check with a coupple of our magnet suppliers. Neodymium would make a smaller magnet but wats fun with that? The problem with neodym is it werry easily gets demanetized, many professional users switch to ferite models after their neodymium monitors stop working when dropped once.
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Old 8th March 2004, 08:04 PM   #6
Nisbeth is offline Nisbeth  Denmark
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AMT, I hope you are familiar with www.adam-audio.de
They have some exploded diagrams/renderings of their tweeter that might be of use to you


/U.
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Old 8th March 2004, 08:21 PM   #7
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Default try here

http://mywebpages.comcast.net/neilan...il/DIYHeil.htm

good source of info .

btw if you're interested in the audio amateur article i could scan and email it for you...it covers making your own diaphragms plus building three different layouts of magnet structure including the classic dipole type

i'm too lazy to build one but i'd like to see someone else try!

gary
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Old 8th March 2004, 08:29 PM   #8
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Default try here

http://mywebpages.comcast.net/neilan...il/DIYHeil.htm

good source of info .

btw if you're interested in the audio amateur article i could scan and email it for you...it covers making your own diaphragms plus building three different layouts of magnet structure including the classic dipole type

i'm too lazy to build one but i'd like to see someone else try!

gary
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Old 8th March 2004, 09:20 PM   #9
OliverD is offline OliverD  Germany
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Thanks for all the info!

I will limit my first try to more or less replicate my old 70's AMT-1. If it sounds at least as good as the original, I might feel motivated to experiment a bit.

For the moment, I'll definitely stick to the original diaphragms and do only the rest.

Can anyone think of a technical reason why they stack metal sheets for the pole piece instead of using a milled iron block? If the reason is only a cost / production issue, I think it will be easier for me to mill the pole pieces from an iron block instead of milling hundreds of small pieces.

I decided to use standard ferrite magnets. My motivation is to get the same sound for less money rather than making marginal improvements by spending hundreds of euros.

The "case" will be milled from aluminium, any technical objections? I could switch to composite materials, too.
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Old 8th March 2004, 10:03 PM   #10
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The "polepiece/difraction lens" was punched out of sheet metal for production cost, nothing else. Neodymium magnets are not better than ferite, just smaller and slightly poor reliabillity, alnico would make a difference ok but impractical. IŽll post information on suitable ferites, getting reply from supplier tomorrow morning
Suitable polyethylene film for diaphragms iŽve got.
If we start from there i propose we go for fieldcoil instead of magnets once we get it to play.
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