Synergy Horn with Heil AMT

Hi all,
I've been lurking for a while... and have thinking about what to do with my Great Heil AMTs that I got a year ago when they went half price with free shipping..

Originally I bought them to make speakers based on Xrk's Kazba but then saw Xrk's post on his Synergy Horn using the AMT in lieu of a compression driver.

My Xki's are *still* away for painting but when I did listen to them prior to painting I absolutely loved them, and so trust Xrk if he says something sounds good. Well he said that the AMT horn was among the best speakers he has ever heard!

So I have read up on the theory of them and how to build them and have played around with the spreadsheet by Bill Waslo (thanks Bill!).

But I have some questions about this process I would love to get some help with.

1) With the ESS Heil AMT, I have read that it has a very small vertical dispersion. Is there any point in going for 40 degrees of vertical dispersion or more? Is even less worth pursuing? The smaller the vertical dispersion of the horn, the shorter it can be made.

2) Likewise with the horizontal, I am currently aiming for 90 degrees, as any less than that makes the horns too big (at the moment with 90 degrees and 390Hz pattern control it is 60cm (23.6 inches) wide, which is as large as I would like in my living room).
Question is, is 90 degrees a good value to go with? My seating position will be about 2-3m from the speakers position. 90 degrees horizontal dispersion *seems* good to me from my seating position, but any thoughts would be appreciated.

3) I am aiming for 390Hz as my bottom horizontal pattern control value, but can anyone advise on the choice for this value? The default the spreadsheet comes with is 385Hz and the manual mentions that something in the range of 200-500 will suit most rooms but any extra information would be appreciated.

4) I believe I have found the woofer to match with the AMT: The Peerless SDS-160F25PR01 Peerless by Tymphany SDS-160F25PR01-08 6-1/2" Paper Cone Woofer Speaker
Sealed it should go from 70Hz to 3000Hz nicely. Ported from 33Hz.
Therein lies my question. I was originally planning on doing a 3-way - a 2-way synergy horn with a bass horn on the bottom, like Xrk's project.
That would mean 1 or 2 of these woofers + the Heil AMT in the synergy horn and then building a ~30Hz bass horn to sit underneath and do from ~30-100Hz.
But then I thought, this woofer ported goes down to 33Hz. Why not have a ported synergy horn that has 1 or 2 of these woofers in it and have an all-in-one synergy horn? I did some modeling in WinISD of the woofer and what volume is ideal and how I would vent it, and settled on 60L box tuned for 33Hz. 2 ports, 6.8cm diameter @ 9.28cm long each. 1st port resonance will be at 1852Hz, and max air velocity will be 5.2m/s @ 33Hz.
Firstly, is that a good idea or a terrible one?
Secondly, do you think 1 of these drivers is enough? Or should I get two each for the left and right channels? I don't plan on listening at ear splitting volumes, but I also don't want to underbuild as well. If I get two for each horn then I will need 100L cabinets as well which is a bit larger.
Any thoughts will be welcome.
Thanks to anyone who shares their thoughts to help me.
 
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I am slowly working on the same project actually. I am trying to design a 3D printed adaptor for the AMT (some info here: https://www.diyaudio.com/forums/multi-way/349546-ess-amt-1-projects-5.html#post6090297) - I chose exactly the same angles - 90 x 40. The 90 is to be the same as the 90 degree front opening angle of the AMT itself for a smooth transition. The adaptor is meant to use 5 mm plywood/foam core board for the horn walls - it can be easily modified for another thickness or to use a flanged horn - the chosen throat size is 140 x 140 mm.

The test print worked pretty well - the model needs to be modified a bit still, with the 90x40 horn there is a pretty tight space to fit the midranges - my goal is also to use 6" midrange - so it needs to fit between the adaptor and the second expansion part.
 
In a horn loaded speaker, the native dispersion of the driver in open air doesn’t t matter if you have a adapter that couples it to effectively impedance match the driver to the horn - a smooth and gradual throat adapter. The driver just needs to push air back and forth. The horn expansion determines the actual acoustic dispersion. 90deg might be kind of wide for most synergies. You have to have good coupling on the woofer and mids too.
 
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Regarding dispersion the horns dispersion is constrained by the dimensions of the throat and the wavefront shape at the throat (in the case of no diffraction features in the horn). So for the AMT as it has a large vertical dimension the horns vertical dispersion will be limited by this if the included angle of the walls is large wrt to the frequency dependent constrain caused by the apature and the wavefront shape. Exactly what angle and frequency I cannot say because the data is not available but some guidance can be obtained from the vertical polar measurements.
 
Seems fair to say that horn loading the Heil AMT is like placing a (insert any conventional cd/horn combo here) into another "horn" with the expectation of being able to manipulate the dispersion pattern from the inserted cd/horn combo.



I can't wrap my head around how that works. Seems like the secondary "horn" will function more like a waveguide/reflector to me. The structure of the AMT, according to the patent seems to have addressed the basic functions of a conventional cd/horn (original Heil AMT did at least).


So, you'd be making a megaphone.
 
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One thing about the AMT in a horn is that the membrane squeezes air between the pleats. This force is not super powerful like titanium diaphragm compression driver, compressing then air in the phase plug chamber. As a result, the AMT coupled horn, doesn’t have the typical +10dB gain you get with other horn loaded dynamic drivers. I have found that the SPL our of a horn loaded AMT is very close to its open air rating - but the directivity is focused. This is with the Heil AMT-1. I am not sure if true for Beyma TPL-150.
 
I think that the original structure design worked to create a similar function of a cd.
You should have a look at the patent as it has a paragraph dedicated to the focus plate arrangement (spacing, etc) and how that is used to couple with open air. The new AMT has larger spacing and I believe, as such, that the coupling is less effective or non existent.



Another observation is that if you've ever done a vertical sweep of the diaphragm you'll notice that dead center (vertical) produces the highest SPL. Moving up or down from there shows a roll off of about 6-7db. This is fixed and I believe is a result of how the diaphragms are fabricated. I don't see how a waveguide could spread a vertical response to a degree that overcomes the diaphragms capabilities. I have tried this to a degree but saw no improvement vertically. In a horn, I expect that higher frequencies would not even see the walls.


The best compromise I've found to help with the sit/stand vertical issue was to tilt the speaker back enough to bring the top edge of the vertical dispersion into the hearing plane of the individual listener. This works.


I have an idea of a diaphragm fabrication that might eliminate the issue of limited vertical dispersion but not here.
 
Thanks to all who have replied, this is all helpful information.

Pelanj: I have seen your thread and am looking forward to seeing how your project turns out! It appears that at 30 degrees vertical we are losing up to 10dB in the treble region already! It appears this driver needs to be basically ear level at all times. At least the horizontal doesn't fare too badly in comparison.

Seeing that 30 vertical is already so bad, there seems little point making the horn for any more than 40 degrees vertical dispersion.

Taking this horn any less than 90 degrees horizontal grows it's horizontal size correspondingly. To get 90 degree horizontal down to 390Hz horizontal control pattern frequency I'm at 60cm wide already...

If I attempt do get 75 degrees horizontal dispersion I go up to 69cm..

===

Can anyone comment on the Horizontal Pattern Control variable?
I have mine set at 390Hz but I'm really not sure what to go for here.. Does anyone have experience with waveguides that go lower than this or higher than this and can comment on any difference it makes, if any?

Also, do ported synergy horns exist? Does my ported design idea look ok? (1 or 2 Peerless SDS-160F25PR01 ported down to 33Hz mating with Heil AMT at ~800Hz crossover)?
 
Also, do ported synergy horns exist? Does my ported design idea look ok? (1 or 2 Peerless SDS-160F25PR01 ported down to 33Hz mating with Heil AMT at ~800Hz crossover)?

Look at Weltersys thread on SynTripi horn. He used a bass reflex on the woofer but that was to get it to 80Hz. I would use the woofers you selected as sealed and go down to maybe 80Hz. A bandpass horn wall injection woofer just isn’t going to go as low as an open face reflex box. Asking it to go to 33Hz is unrealistic given how much air it needs to move through the injection slots. It really needs to be simulated and you will know.

You can use a separate home theatre cube style self powered sub below 80Hz. No need for horn sub unless you want to play really loud like a pro event.
 
I think the vertical dispersion is limited by the field plates which form narrow slots preventing a wide dispersion.


Many pro monitors are designed to have a +/- 45 degree horizontal dispersion, eg ATC.
It is also said that too great a vertical dispersion can seriously compromise SQ because of reflections for the floor, and more so from the ceiling.
 
One thing about the AMT in a horn is that the membrane squeezes air between the pleats. This force is not super powerful like titanium diaphragm compression driver, compressing then air in the phase plug chamber. As a result, the AMT coupled horn, doesn’t have the typical +10dB gain you get with other horn loaded dynamic drivers. I have found that the SPL our of a horn loaded AMT is very close to its open air rating - but the directivity is focused. This is with the Heil AMT-1. I am not sure if true for Beyma TPL-150.

jbl_7_series_708p_8_powered_1486118133_1316221.jpg


Horns and waveguides increase the on-axis efficiency of a radiator by focusing the energy into a narrower beam.

For instance, if you put a loudspeaker on a 90° x 90° waveguide, the energy of the loudspeaker is focused into an angle that 4X as small as if it were on a flat baffle.

The diameter of the throat determines when that stops. For instance, with a throat that's one inch in diameter, there will be nearly no "gain" above 13,500Hz. (13,500hz is one inch long.)

This is why:

1) JBL uses a 0.62" throat on their newer speakers (21,774Hz is 0.62" long)

2) AMTs on waveguides and horns don't see a lot of "gain" (The dimensions are too large.)
 
jbl_7_series_708p_8_powered_1486118133_1316221.jpg


Horns and waveguides increase the on-axis efficiency of a radiator by focusing the energy into a narrower beam.

For instance, if you put a loudspeaker on a 90° x 90° waveguide, the energy of the loudspeaker is focused into an angle that 4X as small as if it were on a flat baffle.

The diameter of the throat determines when that stops. For instance, with a throat that's one inch in diameter, there will be nearly no "gain" above 13,500Hz. (13,500hz is one inch long.)

This is why:

1) JBL uses a 0.62" throat on their newer speakers (21,774Hz is 0.62" long)

2) AMTs on waveguides and horns don't see a lot of "gain" (The dimensions are too large.)

It’s not the size because my 5MR450NDY, about same physical throat size has 10dB+ gain in a horn.
 
Hmm thanks again guys. From further reading it seems that 90x40 is ideal to aim for with a horn.
X, I read the end part to your Trynergy thread thoroughly, and am quite taken with the dipole bass micro Trynergies. (especially with the SB Acoustics SB65WBAC25-4 as the full-range and I'm thinking of 2x SB Acoustics SB16PFC25-8 on each horn for the bass)

To your ears (and from memory), did the horn you make with the Heil AMT offer a *significantly* better experience than your dipole bass micro Trynergy?
If not, then the compactness and more ready-made design of the micro Trynergy appeals greatly for the time being.

However if the Heil AMT version is a significant jump up, then that will give me pause! FYI in this current house I'm in the speakers will have to be near to the back wall, if that makes any difference.
 
The AMT is in a different league as far as clarity and resolution. The Heil AMT-1 is already a world class tweeter (one of the best sounding you can buy at any price), and these used to cost $750/pair and weigh 12lbs each is not fair to compare them to a $30 SB65 that weighs only 3oz. Having said that, the SB65 micro Trynergy is great sounding and much more compact. But they are not as resolving as the AMT-1 based horn.

Building the micro Trynergy will teach you a lot of skills needed to make the bigger and more ambitious AMT based horns. So not wasted effort.
 
I am considering using two 3FE22s in parallel as the midranges - they could be fitted to the adaptor directly.

That would be great if the adapter has flanges for the 3FE22's built in and injection ports as close as possible to the tweeter vertex. I would put them on the top and bottom to avoid disrupting the lateral dispersion, which is more important.

Nice thing with Faital 3FE22 (or 25) is that they come in 16ohm so you can parallel them for 8ohm and get about the correct sensitivity to match with the AMT-1.

Now, once you have the AMT-1 adapter all sorted out, have you ever looked at an adapter for a TPL-150? :)