Acoustic Horn Design – The Easy Way (Ath4)

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#13,302
"The horn we use is unique. We designed it using Earl Geddes' equations and nobody else has anything quite like it: a large Oblate Spheroid designed for a 1.4” throat compression driver. The Oblate Spheroid profile is mathematically the most benign curvature for a given radiation pattern angle. Ours has a 75 degree constant-directivity radiation pattern which gives good coverage over a wide listening area and minimal early sidewall interaction. We paid attention to the details: the horn's entry angle matches the compression driver's exit angle to minimize internal diffraction, and the round-overs are large enough to be effective in the frequency ranges that matter most. "

https://jamesromeyn.com/speakers/main-speakers/bohemian-series/

- Would love to see their measurements. A pity they don't show it, it must be extraordinary 🙂
 
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#13,303
#13,304
mabat said:
ATHEX 460-36, a petal model for casting (or 3D printing).

STL file: https://at-horns.eu/img/athex/ATHEX-460-36-CAST.stl
Click to expand...

This was never so easy:

1690035465208.png
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I've actually never made molds for casting, so now I wonder how to best proceed 😀
(This was a 6-hour print and probably couldn't be made much quicker. That would be 72 hours for a WG pair. I can only hope casting 12 pcs won't take this long.)
 
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#13,306
tmuikku said:
... have you considered /noticed difference with good and bad DI? I would think listening beyond critical distance power response of the speaker is very important, more so than direct sound, while listening closer the direct sound would be more important and lousier DI would do? this would be relevant while tuning a system and a comprimize needs to be made between the two.
Click to expand...
Agreed that in the direct field, the DI is not very important as the room is mostly out of the picture. In the reverb field both the direct sound and the reverberation is important, but I would still consider the direct sound as the more important, especially so for a high DI system.
tmuikku said:
In general, do you think it would be relevant to have listening distance as context in forum discussion or does sound quality on both listening distances depend more or less on same aspects off playback system?
Click to expand...
I think that listening distance as well as expectations (like reproducing large venues vs. a studio recording imaging) as context. I've said this often. These things strongly affect the design goals of the playback system.
 
#13,308
mabat said:
"The horn we use is unique. We designed it using Earl Geddes' equations and nobody else has anything quite like it: a large Oblate Spheroid designed for a 1.4” throat compression driver. The Oblate Spheroid profile is mathematically the most benign curvature for a given radiation pattern angle. Ours has a 75 degree constant-directivity radiation pattern which gives good coverage over a wide listening area and minimal early sidewall interaction. We paid attention to the details: the horn's entry angle matches the compression driver's exit angle to minimize internal diffraction, and the round-overs are large enough to be effective in the frequency ranges that matter most. "

https://jamesromeyn.com/speakers/main-speakers/bohemian-series/

- Would love to see their measurements. A pity they don't show it, it must be extraordinary 🙂
Click to expand...
..except they state the pattern is 75 degrees.

-that’s a hard pass IMO. In fact 110 would be my directive “limit” horizontally.


And yes, all that prose dedicated to a design that’s all about pattern control without actual polar patterns is absurd.
 
#13,312
Isn't it possible to place narrow-radiating speakers closer to the side walls (basically against the wall), using more of the room width than with a wide-radiating one? With a proper toe-in this should give a pretty wide soundstage with still solid image...

(The issue may be that what's nominally narrow is seldom so in a wide range... it's difficult to make narrow that well controlled.)


- The 460-36 is also ~75 deg in the middle of the passband (it somehow fits naturally with a 1.4" throat), but it's not really constant:

1690095560988.png
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#13,313
gedlee said:
Agreed that in the direct field, the DI is not very important as the room is mostly out of the picture
Click to expand...
The forgotten axis appears again.. the distance the direct field extends from the source, on axis, changes per frequency and per directivity....

@mabat Have you ever tried to design a waveguide that seeks to keep the distance of the direct field constant? Seems impossible without setting a figure for how reverberant the listening room will be, but I am not sure. The funny thing is that it would have a rising DI.... intersting. Constant Directivity on the X and Y axis, been there done that... Z axis? Nope.
 
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#13,314
The effect of the direct field is that the direct sound is so strong compared to all the rest, that the details of the rest (like DI) just don't matter much - it's "mostly out of the picture".

- That's also the only option when a direct sound is the only good thing left in a system design 🙂
 
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#13,316
^ You mean to have the polar data calculated also for the vertical plane?

Code: 
ABEC.Polars:SPL_H = {
  MapAngleRange = 0,180,37   ;  start [deg], end [deg], nr. of points
  Distance = 2 ; [m]
  NormAngle = 0  ; [deg]
}

ABEC.Polars:SPL_V = {
  MapAngleRange = 0,180,37
  Distance = 2 ; [m]
  NormAngle = 0  ; [deg]
  Inclination = 90 ; [deg]  ; <----- vertical plane
}
 
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#13,317
Sorry to water down the topic of imaging even more, but I really like Dave Rats thinking:

Any of you that have been down the 2 mic room recording rabit hole?

I've been thinking of recording a musician with two mics - 2 meters apart and then play it back in a different room with the speakers also 2 meters apart.
 
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#13,318
Personally, I like stereo for what is it, it's for amusement during leisure. And it can be pretty rewarding as it is. For me it's not a hunt for perfection but perhaps for a rewarding experience. I don't even think about how "real" it can ever sound. Of course it's all fake. I don't care in the slightest. 🙂
 
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#13,319
I like Dave Rats thinking too.
I find my system much more interesting with the mid horns out wider than the stack of Mid bass / upper mid / tweeter and mids atop, ala Cessaro etc.
I had the system vertical like that for years.
With a wider set up, the sound is much more dynamic and open.

I think Dave's ideas start to work if you mix / master for a diffuse setup.
Trouble is, every diffuse hifi setup would be different and sound different. There would be no standard.
At least L/R channel stereo is a common denominator or standard, that all can work to.

As things stand mixes for stereo give some feeling is position and sound stage, all be it limited, time/phased aligned is the best we can get to.

I do find single point / small speakers rather boring.
After a long time with them my brain does shrink to accept though🙂
 
#13,320
mabat said:
The effect of the direct field is that the direct sound is so strong compared to all the rest, that the details of the rest (like DI) just don't matter much - it's "mostly out of the picture".

- That's also the only option when a direct sound is the only good thing left in a system design 🙂
Click to expand...
Well that is never the issue because without high DI the direct field at higher frequencies will never reach you... hence rising DI... The direct field may reach out 21" at 100hz but only 2.1" at 1000hz.

We are just assuming the direct field is reaching us and/or reaching us at all frequencies but thats inaccurate.

We are saying "if you sit close" you are in the direct field... that is false.

Still, it seems the extension of the Direct Field can be tailored to be constant, or at least more consistent, with proper formulation of directivity, and that Directivity would be a rising DI as higher frequencies will not extend direct field away from the source without the help of directivity and the lower the frequency, the farther the direct field extends on axis, away from the source when DI is constant

For people like myself, who like to sit close and stay on Axis, a rising DI will potentially yield a more consistent sound. Constant DI will always sound more reverberated moving upwards in frequency and more direct moving lower in frequency
 
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