Acoustic Horn Design – The Easy Way (Ath4)

TNT

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BTW, with a bit different mouth shape, I was able to reduce the waveguide diameter from 520 to 460 mm while keeping the performance virtually the same down to ~600 Hz:

(light gray = A520G2, color=A460G2)


It may not seem as much but those 6 cm are a big difference visually.
If one wanted to stay at 520, how could this insight be utilised to ones advantage?

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Staying at 520mm it would just lead to a higher DI around the "knee" -

1717486452968.png


I'm not sure this is the best thing, as it's often problem to reach this with the direct-radiating transdures below.
But it's not a huge difference.
 
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TNT

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OK, we don't want that really no... so making it smaller is the "only payback" for this... maybe one could say that staying at 520 using the invention would enable directivity control at a lower frequency - whatever directivity one would want - wider or narrower..?

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Yes, it enables directivity control to a lower frequency, but with a sharper DI knee where the transition occurs (below some frequency the DI always starts to decrease no matter what, that's simply given by the mouth size). I tend to think this is not as beneficial but these are really nuances.

The current A520G2 (and A400G2 as well) are designed so that this transition is very very smooth. But it we don't need to go below ~600 Hz, it can be made smaller with the same performance. That's really the point.
 
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Hi @mabat, I finally got to test the last version of the adapter.

The measurements aren't accurate, I shoot the ceiling again and just rearrange the adapters.

6 cycles window, 5dB step, mic is always at the same distance from the driver (~90cm), and I tried to place the horn in the same place (so I don't think the difference in the top end is due to microphone/horn position, it was seen on other measurements as well).

T520-36-STD-1 - green
T520-36-EXT-1 - blue
T520-36-EXT-type-B - orange

1717491659022.png


Group delay:

1717492673257.png
 
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Thanks!
It's only a pity you can't take cleaner measurements. At 400 Hz six cycles mean 15 milliseconds, and in that time you collect reflections from all around. But I know very well this is the most difficult frequency range to measure at home, and I don't know how to improve it without a lot more serious effort.

- Now I think if the long adapter isn't just too long here.

The top octave is also a bit of a mystery. I wouldn't expect such differences, but it may be, as it's already above the simple-wavefront mode of operation, I suppose.
 
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It's only a pity you can't take cleaner measurements.
I'm thinking about taking the horn out on the terrace and making a cleaner measurement outside, but I don't know when that will be possible, especially since a building is being built next door and the environment is quite noisy.

The top octave is also a bit of a mystery. I wouldn't expect such differences, but it may be.
It looks like in the top octave the driver's wavefront is far from ideal, so the results will be different with different drivers.
 
Oleg, looking back at your previous measurements, there are so large differences that it's indeed difficult to make any judgements.
The main differences between these measurements: a slightly different scale at the pics; the distance was a bit shorter, ~60-70 cm as I remember vs ~90 cm, and maybe not the same FDW (4/6 cycles? not shure)..

E.g. short adapter, measurements looks closer after scaling (I don't save old measurements, thus by hands):

1717513982537.png


And yes, the colors are reversed, Green 1 = Blue 2, Blue 1 = Green 2. There's a couple dB difference, but I think the difference between adapters is pretty constant overall?

1717513537215.png


I apologize for the inaccuracies in the measurements, I'm doing my best. I will install a new long adapter soon and try to take better measurements.

Maybe I should do not just one measurement per axis, but an average of 5-7 measurements in the listening window from the longer distance, it might be more accurate in common. Or stop supplying poor quality data if it's confusing :)
 

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Maybe I should do not just one measurement per axis, but an average of 5-7 measurements in the listening window from the longer distance, it might be more accurate in common. Or stop supplying poor quality data if it's confusing :)

If you can mount the horn assembly in a way that its more or less free field (gaffa and a sturdy floor lamp?) then you take 8-25 measurements at different distances for each angle, starting with nearfield. Turn the assembly for angled measurements, not the mic. Use Vector Average in REW. You do get a result that resembles a ground plane measurement. At the moment I have only used this method for bass/mid not horns.

It was @mwmkravchenko that mentioned this way of measuring and that he got consistent and solid data from it. He writes that he uses 25 measurements in 10 cm increments in this post: MEASURING

Later it is mentioned that you get good data with fewer measurements. Try it yourself and make your own opinion.
 
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At the moment I have only used this method for bass/mid not horns.
I use a similar method with averaging an array of measurements taken from the couch, as Dirac-live does (they use 9 measurements, the main thing is to randomize the points in space). For room measurements, it works well.

Unfortunately, I don't have a convenient enough stand to bring the horn out into the middle of the room, but I'm thinking about how to organize it, and need free time and ability to make noise when my wife and dog aren't stressing :)

1717755651336.png
 
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TNT

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mabat, as you built your first A520G2 we wonder if you have had the opportunity to stick the rosso to it and had a quick try... how did it look? :)

Where there a problem with the modified exit angel perhaps?

But as You have not published anything I really suppose you have not had the chance to try it yet.... this just to encourage you and tell you that at least one customer is very curious :-D

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