AMT (Air Motion Transformer)

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arivel

arivel

Member
Joined 2014
#1
hello everyone .
I would like to understand in detail how to build an AMT (Air Motion Transformer) .
I visited some links but they make a summary description both in words and images and it is not clear. more than anything they describe the operating principle .
can you tell me where to look for images or videos in which it is clear?.
hi thanks .
 
#3
apparently there are two schools of thought and two ways to build it.
using the magnetic field parallel to the folds of the membrane and the other one that uses the magnetic field perpendicular to the membrane.
i understood how the first method works but not so much the second method.
 
#4
I'm not clear on which orientation you are describing when you say: "magnetic field parallel to the folds of the membrane."

Heil patent
https://patents.google.com/patent/US3832499A/en

There was an article "An Amateur's Version of the Heil Air Motion Transformer" in Audio Amateur Loudspeaker Projects by @Neil Davis that shows several pole arrangements (though the magnetic orientation is the same for them).
 
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#6
mattstat said:
I'm not clear on which orientation you are describing when you say: "magnetic field parallel to the folds of the membrane."

Heil patent
https://patents.google.com/patent/US3832499A/en

There was an article "An Amateur's Version of the Heil Air Motion Transformer" in Audio Amateur Loudspeaker Projects by @Neil Davis that shows several pole arrangements (though the magnetic orientation is the same for them).
Click to expand...
There are many ways to achieve a magnetic field, but it MUST be normal to the current flow. The force vector (movement of the pleats in the diaphragm) is the cross-product of the magnetic field vector and the current vector. You can use the right-hand rule to predict the force. The Audio Amateur article shows the diaphragm before folding (see page 2 of the article). When folded, the current flow will alternate between "up" and "down" for adjacent tracks. You can apply that right-hand rule to see how pleats will either move toward each other, forcing out the front, or move away from each other, pulling air in.
 
#9
Multiple designs of interest at this first thread.
www.diyaudio.com/community/threads/ess-amt-1-in-my-projects.349546/
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www.diyaudio.com/community/threads/attaching-wave-guide-to-a-heil-amt.403372/
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www.diyaudio.com/community/threads/wave-guide-for-midrange-amt.343210/
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https://community.klipsch.com/index...-with-wings-possible-kit-for-heritage/page/7/
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www.reddit.com/r/diyaudio/comments/1gm6wqx/3d_printed_waveguide_for_heil_ess_amt/
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https://www.facebook.com/photo.php?fbid=10153076327306866&id=85313456865&set=a.10151010328041866
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https://josephcrowe.com/products/waveguide-no-1905-for-dayton-amtpro-4-tweeter
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https://audioxpress.com/article/tes...sound-amt-and-xmt200-horn-from-eighteen-sound
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https://www.beyma.com/speakers/Fichas_Tecnicas/beyma-speakers-data-sheet-amt-TPL150H.pdf
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#11
Does anyone know what theory says about using the Heil principle for woofers? Like letting two drivers face each other closely.

Could be that it does not work at low frequencies - did anyone try?

Or maybe using additionaly a front horn both drivers are working on?
 
#14
@mattstat

great. Interesting to make a subwoofer slot loaded to a corner making the system more efficient "for free"

Screenshot_20250211_073237_com.pdfviewer.app.jpg


Maybe slot loading of two drivers facing each other is not necessary. Just giving the driver only one third of its radiating area as opening.

Reminds me of the dimensioning of coupling chambers in horn loudspeakers where the throat size influences velocity with gain of efficiency until distortion of compressed air dominates the result.
 
#15
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#16
Hi i might chip in 🙂 as far as i know there is no hard rules to make one. except dept of pleats and width as most prominent , Bandsei and Solhaga might know the most about the AMT, Bandsei posted my video while he made the most stunning ones i seen !, still here on my bookshelf as a reminder of... well how nice one can be 🙂 in the video Bandsei posted was with the intention of go as low as possible while using cheap ferite magnets (very low efficiency).... to get proper 20Khz without any work on it. go no more then 4-5mm depth of a pleat. pleat width around 1mm wide.

thats about it , width of the total panel dictates dispersion etc as usual , talking resonance is another thing,. i think there is a super long topic about that
 
#18
i think this was the result... but remember really low effciency, and i do think ii added a a notch at 14khz. .. so they should be less deep... but i wanted to go as low as i could. and match my huge blocks of magnet..


aparantly i did manage to get low res. on these and they are 6mm deep 2mm wide... hmm its been to long.ago

 
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