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-   -   Acoustic Horn Design The Easy Way (Ath4) (https://www.diyaudio.com/forums/multi-way/338806-acoustic-horn-design-easy-ath4.html)

mabat 12th February 2020 09:46 AM

Quote:

Originally Posted by onni (https://www.diyaudio.com/forums/multi-way/338806-acoustic-horn-design-easy-ath4-post6081201.html#post6081201)
What's the difference? Size, throat?

Oh I wish I knew.

mabat 12th February 2020 09:53 AM

Quote:

Originally Posted by Ro808 (https://www.diyaudio.com/forums/multi-way/338806-acoustic-horn-design-easy-ath4-post6080828.html#post6080828)
What's that?

The chamber reduced to a minimum, with horn entrance only 1 mm from the source. It may be hard to see from that.

mabat 12th February 2020 04:54 PM

5 Attachment(s)
"Protruding" the walls inward really seems to help. Not quite there yet - some form of knuckles will be needed I guess :) The diagonals start to suffer however.
(Still the same 33 mm throat.)

- This horn I would be satisfied with.

Patrick Bateman 12th February 2020 05:18 PM

Quote:

Originally Posted by mabat (https://www.diyaudio.com/forums/multi-way/338806-acoustic-horn-design-easy-ath4-post6081162.html#post6081162)
Now let me show you something:

- the plots below are for horizontal, vertical and diagonal polars (a 7.5 deg@2m)
- on the left is the M2 clone (shown before) labeled "X", on the right an OS waveguide made squarish, aka "ATH"
- these two have the same throats (33 mm) and are about the same size

ATH has nothing you would call a diffraction slot, I assume. I just can't see where is this M2 clone actually better, having one. I see a tighter pattern control with the ATH overall, it is virtually as good diagonally as horizontally or vertically. What I am missing? I'm sorry but this "optimized diffraction slot" thing seems like a fairy tale to me. At least for a pattern control. I can't comment on HOMs.

https://www.diyaudio.com/forums/atta...horizontal-png

https://www.diyaudio.com/forums/atta...h-vertical-png

https://www.diyaudio.com/forums/atta...h-diagonal-png

https://www.diyaudio.com/forums/atta...th4-x_abec-png

https://www.diyaudio.com/forums/atta...4-ath_abec-png

Fundamentally, the way that horns and waveguides work is that they take the same amount of energy and they focus that energy into a narrower beam.

A round oblate spheroidal waveguide will 'illuminate' the room consistently. IE, the sound on the vertical axis is identical to the horizontal axis and is identical to the diagonal axis.

The JBL "high definition imaging" waveguides have a diffraction slot that's shaped like an "X."

The diffraction slot does three things:

1) it narrows the directivity on the diagonal axis

2) it widens the directivity of the horizontal and the vertical axis. I like to describe this as "robbing Peter to pay Paul." Basically the HDI waveguides improve the response on one axis by degrading the response on another.

3) When sound radiates into a narrower beam, the output goes UP. Because the volume of an HDI waveguide is smaller than an oblate spheroidal waveguide, the HDI waveguides are more efficient.

These three things are illustrated in your simulations. Note that the HDI waveguide has similar beamwidth to the oblate spheroidal waveguide, but the HDI waveguide is 3dB more efficient at 2khz.

mabat 12th February 2020 05:23 PM

Quote:

Originally Posted by Patrick Bateman (https://www.diyaudio.com/forums/multi-way/338806-acoustic-horn-design-easy-ath4-post6081714.html#post6081714)
...
2) it widens the directivity of the horizontal and the vertical axis.

It doesn't, just look at the data. The same beamwidths can be achieved without it so how can you say that it widens the directivity?

Patrick Bateman 12th February 2020 05:35 PM

Quote:

Originally Posted by mabat (https://www.diyaudio.com/forums/multi-way/338806-acoustic-horn-design-easy-ath4-post6081722.html#post6081722)
It doesn't, just look at the data. The same beamwidths can be achieved without it so how can you say that it widens the directivity?

That's a good point:

A big part of the reason that I'm fascinated by the HDI waveguides is because I've found that wide beamwidth waveguides don't behave as simulated in the real world.

For instance, I've 3D printed waveguides that were 33cm wide, which performed no better than a 16.5cm waveguide.

From simulations that I've done in ABEC, I believe that what's happening is that the wavefront radiated by the compression driver can't expand fast enough. Due to this, the waveguide behaves as if the walls of the waveguide aren't there.

My 'hunch' is that this is happening because some waveguides produce a converging wavefront, some produce a diverging wavefront, and some produce a flat wavefront.

The JBL HDI waveguides sidestep a lot of this, because the walls are 'pinched.'

In addition to this, there's a couple other reasons to use the HDI waveguides:

1) they look cool

2) they produce higher SPL than an O.S. waveguide

I'm not saying they're the greatest thing on earth, just saying that I'm a fan. If you prefer oblate spheroidal, that's perfectly reasonable, OS performs really well.

mabat 12th February 2020 06:01 PM

I'm not a fan of any particular shape, I only can't stand beaming sources, so of those I'm really not a fan. I look at the data and when it contradicts the claims I would like to get straight what's going on, possibly to understand it better. The last explanation I would accept is that there is some mysterious phenomenon that's hard to grasp. :)

mabat 12th February 2020 06:11 PM

4 Attachment(s)
Hey, this looks fine (374 x 336 mm) -

ThroatDiameter = 33 ; [mm]
ThroatAngle = 0 ; [deg]
Coverage_Horizontal = 110; [deg]
Depth = 120 ; [mm]
SE_s = 0.7
SE_n = 4.0
SE_q = 0.995
Depth.ConicSectionPart = 1.0
Shape = raw2rect
Shape.FixedPart = 0.01
Shape.CornerRadius = 40 ; [mm]
Shape.StretchExp = 3
ShapeCurve = SF
SF = 1.65,2.3,4,2,5.1,2.9
SF.Rot = 0

; Mesh Setting
Mesh.AngularSegments = 100
Mesh.DepthSegments = 28
Mesh.CornerSegments = 10
...

Patrick Bateman 12th February 2020 06:16 PM

What are you using to do your renders?

I tried POV Ray but the results weren't great:

https://imgur.com/i0cRd8e.png

mabat 12th February 2020 06:21 PM

1 Attachment(s)
Meshmixer. With a few clicks, hard to beat.


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