http://www.diyaudio.com/forums/planars-exotics/2651-ess-amt-1-air-motion-transformers-12.html
I've posted this on the Geddes Waveguide thread and the thread linked above, but this subject probably deserves its own thread. The design started out with the MDF edgeround projecting into the throat, but the projection worked out to be greater than anticipated so was ground down. The gap between the assembly and the heil will be coupled with foam window gasketing to make the transition smooth but removable, and the triangular piece in contact with the AMT frame has bondo filling the gap to the rest of the horn flare. The expansion is straightwalled with a roundover to a short flat section then a round-back. According to the behavior of horns with compression drivers, and the simulations run by our own Mige0 here: Dipole Horn, Dipole Directivity Control Device
this should maintain CD exceedingly well. I'm undecided about whether to include the top section or not, it seems like it's unnecessary as there's already dipole cancellation and the directionality imposed by the 4" vertical dimension taking place. Perhaps just a soft absorber to dampen any reflections off the top edges of the MDF?
Let me know what you think!
I've posted this on the Geddes Waveguide thread and the thread linked above, but this subject probably deserves its own thread. The design started out with the MDF edgeround projecting into the throat, but the projection worked out to be greater than anticipated so was ground down. The gap between the assembly and the heil will be coupled with foam window gasketing to make the transition smooth but removable, and the triangular piece in contact with the AMT frame has bondo filling the gap to the rest of the horn flare. The expansion is straightwalled with a roundover to a short flat section then a round-back. According to the behavior of horns with compression drivers, and the simulations run by our own Mige0 here: Dipole Horn, Dipole Directivity Control Device
this should maintain CD exceedingly well. I'm undecided about whether to include the top section or not, it seems like it's unnecessary as there's already dipole cancellation and the directionality imposed by the 4" vertical dimension taking place. Perhaps just a soft absorber to dampen any reflections off the top edges of the MDF?
Let me know what you think!
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Ahh, haven't noticed you already have built it.
Anyway. Give it a try "as is" and possibly follow my suggestions later on if you think it's worth the effort.
I have only seen drawings of the ESS so far but what I remember the roughly 90 deg front is *not* the contour you are looking for to match.
What IMO is to look for is the *internal* contour and this one IRC is plain 0 deg.
So - your own contour should start out with a smooth transition to that 0deg - opening up to the 90deg (included) you prefer.
Michael
Hm, upon reviewing, I see what you're saying. Perhaps I'll kerfcut the dickens out of a few pieces of ply and give one of the more constricted throat profiles a shot. In retrospect, I wish I'd simply used kerfcutting to make this assembly. I'm not convinced that the more constricted throat is desirable however, as I see the increasing directivity with frequency of that profile style to be a negative. We'll find out when I test this one!
Any thoughts on the vertical component?
ESS Great Heil Air-Motion Transformer | Parts-Express.com
Any thoughts on the vertical component?
ESS Great Heil Air-Motion Transformer | Parts-Express.com
An externally hosted image should be here but it was not working when we last tested it.
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In general - with what dimension you start out into the horn has nothing (or at least not that much) to do with the directivity you end up with - if you meant it that way.
It has more to do with the "top end" control of the horn / waveguide.
So - if you are in OS style waveguide you could start with a simple roundover into the conical section right at the place where the slits end - making no use of the 90deg (incl) angel part of the Heil at all.
Not at the time being - I have some ideas but have to check out first which is most unlikely to happen this year.
I'd very much appreciate if you could do some measurements even before doing any "improvements" and post the IR files.
This would give me - and others - the opportunity to do some analysis I'm particularly interested in.
Michael
It has more to do with the "top end" control of the horn / waveguide.
So - if you are in OS style waveguide you could start with a simple roundover into the conical section right at the place where the slits end - making no use of the 90deg (incl) angel part of the Heil at all.
Not at the time being - I have some ideas but have to check out first which is most unlikely to happen this year.
I'd very much appreciate if you could do some measurements even before doing any "improvements" and post the IR files.
This would give me - and others - the opportunity to do some analysis I'm particularly interested in.
Michael
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Hm. I guess only measures will tell us. My measurement setup is rough (it's generally enough to tell me whether a concept is working as intended or not, which is sufficient for me), but I can certainly confirm if it's imposing directivity as intended. One follows the other, so far as horn action and directivity are concerned. I certainly hope that I'm getting reasonable cylindrical propagation, as these things have been something of a pain to get up and running 🙂
The horn action on the Beyma TPL-150H doesn't seem to be at the mercy of a constricted throat, however, it appears to have the coverage angle defined by the angle of incidence in the throat, as it's a straight-wall profile until the termination roundover.
The horn action on the Beyma TPL-150H doesn't seem to be at the mercy of a constricted throat, however, it appears to have the coverage angle defined by the angle of incidence in the throat, as it's a straight-wall profile until the termination roundover.
Cool looking project! Can't wait to see some measurements. I'm currently back in LA, so if you want some help, I've got a functional measurement setup. How wide is the whole thing?
http://www.diyaudio.com/forums/plan...t-1-air-motion-transformers-6.html#post295226
This is the best (horizontal) polar I know of. I have a suspicion that the 1k hump represents a dipole peak before the bottom end rolloff. I am hoping that the peaky polars are largely due to interference patterns from the harsh termination of the "horn".
This is the best (horizontal) polar I know of. I have a suspicion that the 1k hump represents a dipole peak before the bottom end rolloff. I am hoping that the peaky polars are largely due to interference patterns from the harsh termination of the "horn".
People get easily impressed by the fancy look of - and the countless legends about the Heil speaker.
But from a mere speaker design point of view any modern AMT is light years ahead.
Meaning – for a new design (contrary to retro-design) and especially for any waveguide / horn / diffraction alignment design you are far better off with the almost perfect wavefront (in the frequency range of interest) released by AMT's from Beyma, Mundorf, etc.
But as you already have the Heil at hand – just give it a try.
There are pretty nice applets out there to visualize (more or less) how the released wavefront of the Heil might look like, but its possibly not of much help for you beyond what I've said.
Michael
Nothing new to report.... I had my sander out on loan and it took some time to get it back (ain't it always the way?) and since haven't had the time to work on it. I'll try to hop back on the ball in the next week or three and get them finalized, and some measurements taken (though likely rough, RTA based stuff at first).
Hello and sorry for the tangent, but what a pleasure to see interest in the AMT! I had a pair of 1B Bookshelf in the late 70s, then a pair of 1B (truncated pyramids), for years and years. How wild to see that ESS offer it as a DIY component!
I seem to remember that one version of the diaphram had a very subtle matrix over it, to prevent it from distending...and whatever ESS did with the AMT 1D, I didn't like it nearly as much.
Back in 2001, I noted a German company producing a line of monitors with advancements upon the original HEIL:
X-ART | ADAM Audio GmbH
I don't know if they sell the mids or tweeters separately...but I can say as an owner since 2001, that they are truly outstanding, and represent something which must be heard...the new tweeters are also in a line of budget monitors and might be detached and placed into something DIY...best on your projects!
I seem to remember that one version of the diaphram had a very subtle matrix over it, to prevent it from distending...and whatever ESS did with the AMT 1D, I didn't like it nearly as much.
Back in 2001, I noted a German company producing a line of monitors with advancements upon the original HEIL:
X-ART | ADAM Audio GmbH
I don't know if they sell the mids or tweeters separately...but I can say as an owner since 2001, that they are truly outstanding, and represent something which must be heard...the new tweeters are also in a line of budget monitors and might be detached and placed into something DIY...best on your projects!
I think Harwood is just a EU sellers re-labeleing of Aurum Cantus - but that does not tell me any more 😉
http://www.diyaudio.com/forums/planars-exotics/157372-amt-new-player-game.html#post2044790
IMO thy are nowhere as top notch as the big boys but still may offer be a good bang for the buck .
Michael
http://www.diyaudio.com/forums/planars-exotics/157372-amt-new-player-game.html#post2044790
IMO thy are nowhere as top notch as the big boys but still may offer be a good bang for the buck .
Michael
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I like the approaches on hornloading the AMTs.
But i have a question:
Which specific difference/advantage can result
from hornloading such a planar driver compared
to a conventional say compression driver ?
There has been a study, stating that differences between
transducer concepts in tweeters are quite inaudible
under anechoic conditions and with level and
FR compensated.
http://www.ak.tu-berlin.de/fileadmin/a0135/Magisterarbeiten/Andreas_Rotter_MagA.pdf
So one of the most important audible differences
between types of tweeters could in fact be the dispersion
pattern ... which is now dominated by the wave guide ?
But i have a question:
Which specific difference/advantage can result
from hornloading such a planar driver compared
to a conventional say compression driver ?
There has been a study, stating that differences between
transducer concepts in tweeters are quite inaudible
under anechoic conditions and with level and
FR compensated.
http://www.ak.tu-berlin.de/fileadmin/a0135/Magisterarbeiten/Andreas_Rotter_MagA.pdf
So one of the most important audible differences
between types of tweeters could in fact be the dispersion
pattern ... which is now dominated by the wave guide ?
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