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Heil Air motion transformer for Cornwalls


jwgorman
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I read that very article last night. I have been trying to find the AMT manufacturer but no luck yet. Good picture you found for size reference.

 

Hopefully by end of next week i will have my dual AMT prototype built. Then we can see just what a similar horn will do. I don't plan on curbing the sides though.

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Thanks to [mention=26262]Chris A[/mention] I became aware of the AMT driver while discussing REW measurements.  Out of curiosity, I ordered a pair and have been playing around with them.  I have been running all sorts of measurements on them to see what they can do when mated with my bass bins.  Some waveguide prototypes indicated an increase in lower end performance.  This is a very simple build with just a pair of 'wing's added to the sides.  Adding a top to the driver audibly killed the spacious, airy sound of the driver.
 
As soon as I get time I will formally build the waveguides.  I have also decided to stack a pair of drivers on each speaker. In theory, this should have a net benefit vs. a single driver. 
 
If you guys are interested, I can post my measurements and results as I go along. 
 
So far, I have found the many reviews I have read to be correct.  This is an incredible driver with superb upper end resonse.  It does lag a little bit in the 1-2khz region, right where I wish to crossover.  However, my tests indicate that with the addition of the waveguides, I can improve the lower end response.  As [mention=26262]Chris A[/mention] will attest, I am no expert on this stuff and have relied quite a bit on Chris to help me along the way. Most of you are better versed to understand much of this, so if I make errors, please point them out.
 
I tried two types of wave guides.  The best performer was the one with the front 'wings' only.  I also measured the effect of sticking an AMT inside an Oris horn.  Results were predictably awful.
 
 
FrontWG.jpg.11c97dd7decb4defeaed418b4437d233.jpg
XconfigurationWG.jpg.26c9672f4e176cd83cacda07e3533e82.jpg
InOrisS.thumb.jpg.22c2d5a318c2f9b626e8712b981b2ff4.jpg
What if you kept extending the wings to make it like a horn with the top cut off?

Sent from my SM-T830 using Tapatalk

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On 12/18/2019 at 11:50 AM, Rudy81 said:

Sounds like a good opportunity to cooperate and compare notes.  When I ran the first prototypes, I found the X setup did not perform quite as well as the front waveguide only idea. However, before I go in for a full build, I want to run those tests again with a more critical eye on response.  Compared to my other builds, this will be a piece of cake, but I want to optimize the waveguide.   Let us know what you find out in your experimentation.

 

I found that the X configuration has a -2dB dip centered around 850hz.  Otherwise, it is the same as just the front waveguide design.

Great idea. It's pretty far down the list for me, but you never know what can develop on a cold winter night in 2020!

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I know there is at least one very good thread on diy audio about waveguide design for AMTs. a member there did some experimentation with a design similar to what @Rudy81 has done. I will try to dig up a link.

 

Another thing to think about is, the original ESS AMT 1s, rock monitors etc. had the AMT on top of the speaker towards the front. The sides and front allowed the sound to exit, but the top and back were a solid panel. Given the dipole nature of the driver the back wave would be reflected inside the enclosure and exit the side. Has anyone thought about positioning the AMT somewhat on front of a large horn instead of positioning it at the throat like a conventional compression driver.  In essence using the horn to reflect the back wave?

edit: I believe the backs of the top area of the ESS speakers was open. The top is a solid panel though. I will have to check mine when I am home. I do still wonder if there is something though to controlling the back wave and making a “waveguide” that is a fixed shape and distance from the AMT. 

 

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Are you looking for this thread? https://www.diyaudio.com/forums/planars-and-exotics/171441-hornloading-heil-amt1.html

 

Actually, I got my thoughts from that thread.  I have been in contact with one of the guys there who had some success in their build.  Although, they have gone on to other speaker types and builds.

 

My current goal is to be able to lower the usable frequency of the driver just a bit and, using a horn, boost the performance at the 1-2khz region.

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  • 2 weeks later...

I've moved my entry on the double-stack AMT-1 with wings to a new thread in honor of its likely capability of turning into a kit for Klipsch Heritage models (Klipschorn, La Scala, Belle, Cornwall, Heresy) having collapsing polar midrange horns. Here's the link:

 

https://community.klipsch.com/index.php?/topic/188177-double-stack-ess-amt-1-with-wings-possible-kit-for-heritage/

 

Chris

 

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Chris, thanks for running the EQ parameters.  Based on the success of the very simple wing design, I am moving ahead with painting them.  Today might be a good day to shoot lacquer on those if the humidity doesn't get up too high. Might as well finish them properly and then go on to more formal listening tests.  It will, however, take a good week before I can bring them in the house.  The lacquer can seriously stink up the house if I bring them in too soon.  Don't want to upset the wife this early in the year. 

 

 

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  • 2 weeks later...
  • 1 year later...

Hi @Chris A @Rudy81and everyone else that's measured their Heil AMTs.

 

Does the impulse response shape of Figure A for my tweeter impulse response look wired in correct polarity? Or is Figure B further below is the correct polarity?

 

Figure A has the sharp negative dip before the peak and Figure B doesn't. I've read on some forums that Heil AMTs are internally wired in reverse so this is confusing to me.

 

I'm colour blind (I can't tell which wire is which colour) so need to rely on measurement to determine 🙂 

 

Thanks in advance

 

 

[Figure A] :

image.thumb.png.a18182f93499cd187b66e83547994bb1.png

 

 

 

Here is what I get when I reverse the wires:

 

[Figure B] :

image.thumb.png.b6e33f24dce79fed9ce6f2588b9664e4.png

Edited by klipschforum
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I think that if you're using passive crossover filters, the second figure looks a bit more like a normal impulse response.  If you can plot the step function (the integrated impulse response), you can see this more clearly.

 

It turns out that there is a tradeoff in the polarity of the driver vs. the lower frequency driver.  If you're using a DSP crossover, you can sometimes push the phase of the higher frequency driver closer to the lower frequency one, but you have to play with the higher frequency driver's channel delay to do that.

 

Chris

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On 5/1/2021 at 1:00 AM, Chris A said:

I think that if you're using passive crossover filters, the second figure looks a bit more like a normal impulse response.  If you can plot the step function (the integrated impulse response), you can see this more clearly.

 

Hi @Chris A

 

Those plots above are with no crossover in place. 

 

It's the individual driver plots.

 

 

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On 5/5/2021 at 7:43 AM, klipschforum said:

Those plots above are with no crossover in place. It's the individual driver plots.

 

If that's true, then there is apparently something else occurring, since the plots do not appear to be symmetric but opposite in polarity.

 

How did you take the measurements?

 

Chris

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  • 4 weeks later...

Just for fun..

 

I videoed a Heil AMT in action at 750Hz driven by 3 watts (4Ω) just to see what the pleats were really doing. I used a frequency adjustable stroboscope to visually slow down the motion of the pleats, but this is a real time video - thus the irritating 750Hz is there to hear as well. I suggest muting your computer speakers and running the video in a loop.

 

Heil AMT in Action

 

What I noticed

Approx. the 20% top and bottom of diaphragm moves very little, thus the primary output produced by middle 60% section. Additionally, approx. 20% outside edges of diaphragm move very little as well. This would be due to the magnetics or edge stiffness or both. Downside: reduced max SPL at a given distortion level. Upside: the reduced drive area acts like a smaller tweeter, thus resulting in wider dispersion.

 

God bless you and your precious family - Langston

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10 hours ago, Langston said:

I videoed a Heil AMT in action at 750Hz driven by 3 watts (4Ω) just to see what the pleats were really doing. I used a frequency adjustable stroboscope to visually slow down the motion of the pleats, but this is a real time video - thus the irritating 750Hz is there to hear as well. I suggest muting your computer speakers and running the video in a loop.

 

Heil AMT in Action

 

 

Select 0.25 Playback Speed in settings for video and expand screen and you can visualize the movement easier. You can also pause the video and scroll for movement details.

 

miketn

 

 

 

85FFE2DD-7DC6-4C21-9E2E-D16083E9EBE6.thumb.png.9e0026453f226a11550cbeb4a53e0be1.png

 

 

 

 

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