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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 13th September 2019 11:06 PM

Sure. When made large enough in a large enough free space, a gated impulse response will make the baffle look virtually infinite. That should work. The good thing is that you don't need to get very much down low in frequency, so you don't need a long time window.

Looking forward to your results!

mabat 18th September 2019 01:37 PM

2 Attachment(s)
For anyone's interest, this is the radius of curvature of the OS profile for the first 100 mm - for 1" and 2" throats, 90 deg coverage.

Code:

# Gnuplot code

set terminal pngcairo size 1200,1000 font "Helvetica,12"
set output "oswg.png"

rt = 25
alpha = 45

set angles degrees
k = rt*rt
q = tan(alpha)
q = q*q
pow3(x) = x*x*x

wg(x) = sqrt(k + q*x*x)                                # OS profile
wg1(x) = atan(q*x / (sqrt(k + q*x*x)))          # first derivative
wg2(x) = q*k / sqrt(pow3(k + q*x*x))            # second derivative
rk(x) = sqrt(pow3(k + (q + q*q)*x*x)) / (q*k)  # radius of curvature

set title sprintf("OSWG radius of curvature: dt=%g mm, alpha=%g deg", 2.0*rt, alpha)
set xrange [0:100]
set xtics 10
set xlabel "x [mm]"
set logscale y
set ylabel "R [mm]
set grid

plot rk(x) lw 2 not


mabat 18th September 2019 02:11 PM

2 Attachment(s)
First and second derivative. Waveguide with a smaller throat approaches a cone a bit faster, i.e. it is less prone to curvature mismatch at the joint (as talked about eariler).

mabat 18th September 2019 04:11 PM

2 Attachment(s)
Finally, radius of curvature for the three common throat sizes in comparison, and wall slopes.

mabat 18th September 2019 04:47 PM

1 Attachment(s)
Corresponding actual profiles :)

mabat 18th September 2019 05:30 PM

1 Attachment(s)
This is for a throat entry angle of 25 deg (wall to wall) - some drivers do have exit angle this large. I still wonder whether it helps in shaping a spherical wavefront in the end (?). I guess it should but then a spherical wave at the throat entrance would be assumed. And that may be the catch.

mabat 19th September 2019 10:48 AM

1 Attachment(s)
What would be a better junction point, A or B?

Dave Zan 19th September 2019 12:03 PM

Quote:

Originally Posted by mabat (https://www.diyaudio.com/forums/multi-way/338806-acoustic-horn-design-easy-ath4-post5919088.html#post5919088)
What would be a better junction point, A or B?

I don't understand the question.
Can you provide some context?

Best wishes
David

mabat 19th September 2019 12:26 PM

The question is where to cut a clothoid to be joined to a hyperbola, A and B are the two possible places. In the current release of the tool it is allways cut in the middle (between A and B) and connected to a hyperbola disregarding curvature of the latter - that is wrong. I need to find a point of the same curvature on the clothoid and take if from there. I can do it either in point A or in point B, the curvature is the same.

I would tend to choose B but it could be made as an option.

Dave Zan 19th September 2019 12:41 PM

Quote:

Originally Posted by mabat (https://www.diyaudio.com/forums/multi-way/338806-acoustic-horn-design-easy-ath4-post5919149.html#post5919149)
The question is...
I would tend to choose B but it could be made as an option.

Now I understand.
If it was an option then it would be educational to see what difference it makes.

Best wishes
David


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