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.
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.
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.
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.
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/spkrbldr/sbbilist.htm
back ussues available for $18 at http://www.audioxpress.com/magsdirx/spkrbldr/sbbilist.htm
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
http://www.torcman.de/shop/index.html?magnete.htm
or
http://www.supermagnete.ch/magnets.php?at=Q
Regards
Charles
I use the AMT 1A and cant do without, so i´d 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, i´ll 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.
Will go for making diaphragms also. Magnets are pretty basic ferit material, assemble from smaler standard blocks is ok, i´ll 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.
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.
They have some exploded diagrams/renderings of their tweeter that might be of use to you
/U.
try here
http://mywebpages.comcast.net/neilandbarbaradavis/DIYHeil/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
http://mywebpages.comcast.net/neilandbarbaradavis/DIYHeil/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
try here
http://mywebpages.comcast.net/neilandbarbaradavis/DIYHeil/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
http://mywebpages.comcast.net/neilandbarbaradavis/DIYHeil/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
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.
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.
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. I´ll post information on suitable ferites, getting reply from supplier tomorrow morning
Suitable polyethylene film for diaphragms i´ve got.
If we start from there i propose we go for fieldcoil instead of magnets once we get it to play.
Suitable polyethylene film for diaphragms i´ve got.
If we start from there i propose we go for fieldcoil instead of magnets once we get it to play.
AMT-freak said:
Well I could suggest it reduces hysteris the same way laminated
inductor and transformer cores do, but I've never seen it in a
loudspeaker magnetic circuit.
In loudspeaker magnetic circuits laminations are definetely
not a good idea, due to losses through the laminations.
Probably the sheets were pressed, not milled, and for
pressing the thinner the material the easier it is.
sreten.
re:laminated pole peices
The pole peices are laminated to reduce Eddy currents. When the magnetic flux changes, due to a signal in the coil, the flux changes, which induces an opposing current in the pole piece. Laminating the poles in conventional speakers reduces the voice coil inductance, so I've heard. Surprised about the comments on neodymium nagnets;- they are used in brushless dc servo motors, and I thought they had such a square B/H curve that they'd be difficult to de-magnetize.
The pole peices are laminated to reduce Eddy currents. When the magnetic flux changes, due to a signal in the coil, the flux changes, which induces an opposing current in the pole piece. Laminating the poles in conventional speakers reduces the voice coil inductance, so I've heard. Surprised about the comments on neodymium nagnets;- they are used in brushless dc servo motors, and I thought they had such a square B/H curve that they'd be difficult to de-magnetize.
Ingvar, I seem to have overlooked you post. Thanks for your input.
So I will definitely try the "whole block" instead of "stack of sheets" approach - easier to mill for me. I consider the probability to accidentally find suitably shaped sheets in large quantities quite low, but you never know...
I also contacted some German suppliers and expect pricing information tomorrow. However, 125 x 50 x 18 ferrite blocks magnetized through the thickness are hard to find.
BTW, do you think an aluminium case instead of the cheapish plastic will have an impact on sonics? I'd like to make the case as rugged as possible. In case the bare metal surfaces harm the sound through reflections, wood, velvet or cork can be used to avoid this problem.
How are you going to apply the conductors?
A light-weight AMT for a change? I think I still prefer magnets as a simple and cheap approach. The field coil's supply noise + hum will couple through to the sound output, even if we connect the coils in a way that power supply issues are cancelled out (to a certain degree, that is).
We would have to read through all the power-supply-which-triple-of-caps-to-chose threads on the forum then.
On the other hand, if we make a full-range AMT, an adjustable field coil supply would make for a perfect volume control, wouldn't it?
So I will definitely try the "whole block" instead of "stack of sheets" approach - easier to mill for me. I consider the probability to accidentally find suitably shaped sheets in large quantities quite low, but you never know...
I also contacted some German suppliers and expect pricing information tomorrow. However, 125 x 50 x 18 ferrite blocks magnetized through the thickness are hard to find.
BTW, do you think an aluminium case instead of the cheapish plastic will have an impact on sonics? I'd like to make the case as rugged as possible. In case the bare metal surfaces harm the sound through reflections, wood, velvet or cork can be used to avoid this problem.
How are you going to apply the conductors?
A light-weight AMT for a change?
I think I still prefer magnets as a simple and cheap approach. The field coil's supply noise + hum will couple through to the sound output, even if we connect the coils in a way that power supply issues are cancelled out (to a certain degree, that is).We would have to read through all the power-supply-which-triple-of-caps-to-chose threads on the forum then.
On the other hand, if we make a full-range AMT, an adjustable field coil supply would make for a perfect volume control, wouldn't it?
To keep you updated...
I was offered ferrite block magnets, 131 x 51 x 17.5 mm, "Oxyd 300", anisotrop, axial magnetized for about 12.50 Euros per piece in single quantities (including VAT, excluding P&P).
So we would get away with 50 Euros for the magnets plus 60 Euros for original ESS diaphragms. The iron and aluminium comes from the junk yard. Add some bucks for good looking screws, and that's it!
Hopefully I'll be able to post some pics from my disassembled original AMTs this week.
I was offered ferrite block magnets, 131 x 51 x 17.5 mm, "Oxyd 300", anisotrop, axial magnetized for about 12.50 Euros per piece in single quantities (including VAT, excluding P&P).
So we would get away with 50 Euros for the magnets plus 60 Euros for original ESS diaphragms. The iron and aluminium comes from the junk yard. Add some bucks for good looking screws, and that's it!
Hopefully I'll be able to post some pics from my disassembled original AMTs this week.
The cat cot tangled up in my first attempt for diaphragm, thin alluminium wire, sprayglue, polyethylenfilm and cats makes a mess. I´ll go for replacement diphragms for start but try with heat laminating film and wire instead of glue, anyone want a cat for loan a coupple of days give me a note.
Rumours in the late seventies said Oscar Heill actually made a fullrange AMT, large, about 500Kg.... so either we buy forklifts or go for fieldcoils
Rumours in the late seventies said Oscar Heill actually made a fullrange AMT, large, about 500Kg.... so either we buy forklifts or go for fieldcoils
Re: To keep you updated...
Gedday AMT man,
I also am an AMT1 (Heil) owner and would like to
experiment with building more / optimisation of design.
Your idea of rare earth mags sounds good, maybe alnico
better (if you can find appropriate size).
The ticket for this party is to CAD design the "sandwich" plates
to perfectly fit magnets and form an appropriate short
horn section. The original ESS AMT's were turret punched
mild steel which is somewhat restrictive to shape or "form"
however these days Laser cutting is the go. The gen tolerances
acheivable with Laser is 0.1mm, and any shape is possible.
So if you are interested, myself being a design engineer,
can do the CAD work and generate the sections and lay them
out on a typical 1800x2400 sheet, generate a DXF and all you
do is give it to your local laser cutter
The sections can accomodate the magnets or whatever horn
form is desirable for the "mouth" of the AMT. You can also cut
some internal tooling holes to slide a vertical aluminium dowel
for alignment of the plates or maybe just use some SS threaded
rod with nuts on top bottom.
Let me know if you are interested, however currently I am
*very* busy with large projects. So you guys have to do a lot
of the nutting out and sourcing of stuff. I can do design and
generate the profiles but only when I can fit it in.
PS what is the situation with patents on this design?
Cheers,
Terry
AMT-freak said:
Gedday AMT man,
I also am an AMT1 (Heil) owner and would like to
experiment with building more / optimisation of design.
Your idea of rare earth mags sounds good, maybe alnico
better (if you can find appropriate size).
The ticket for this party is to CAD design the "sandwich" plates
to perfectly fit magnets and form an appropriate short
horn section. The original ESS AMT's were turret punched
mild steel which is somewhat restrictive to shape or "form"
however these days Laser cutting is the go. The gen tolerances
acheivable with Laser is 0.1mm, and any shape is possible.
So if you are interested, myself being a design engineer,
can do the CAD work and generate the sections and lay them
out on a typical 1800x2400 sheet, generate a DXF and all you
do is give it to your local laser cutter
The sections can accomodate the magnets or whatever horn
form is desirable for the "mouth" of the AMT. You can also cut
some internal tooling holes to slide a vertical aluminium dowel
for alignment of the plates or maybe just use some SS threaded
rod with nuts on top bottom.
Let me know if you are interested, however currently I am
*very* busy with large projects. So you guys have to do a lot
of the nutting out and sourcing of stuff. I can do design and
generate the profiles but only when I can fit it in.
PS what is the situation with patents on this design?
Cheers,
Terry
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