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7th October 2012, 05:18 AM  #2891  
diyAudio Member
Join Date: Jun 2007

Quote:
I can save you some thinking time  the approximation of a parabolic segment using multiple conical segments will not be included in Hornresp :). It is a relatively easy matter though, to set up a simple spreadsheet to calculate the required AkAbak inputs  see attached screenprint. I can email you a copy of the .xls file if you like. Kind regards, David
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7th October 2012, 09:29 PM  #2892 
diyAudio Member
Join Date: May 2006

Thanks, that would be great! I hope you didn't make that spreadsheet just for me though. It would make me feel bad to monopolize your time on stuff that doesn't directly involve Hornresp. But still, thanks!

8th October 2012, 01:40 AM  #2893 
diyAudio Member
Join Date: May 2009
Location: New Zealand

I have some code that appears to work by similar means to David's spreadsheet.
1: Given Y = A * X squared, we have two pairs of XY values so we can find the value of A. Because we are working in areas, X squared = area / pi. 2: Parabolic horn curves have more "bend" near the throat and are "straighter" towards the mouth. A good approximation is to make each segment twice as long as the preceding segment as you proceed from throat to mouth. For a 4 segment horn, the segment lengths will be 1x, 2x, 4x, 8x the first segment length. So divide the horn length (distance from throat to mouth) by 1+2+4+8 = 15. The segment lengths will be 1/15, 2/15, 4/15, and 8/15 of the horn length. 3. Using the formula from before, calculate the area at each of the segment joins. My script is written in an obscure scripting language (REXX). My plan is to find some free time (ha ha) to convert the script to a spreadsheet so it will be useful to others. 
8th October 2012, 07:26 AM  #2894 
diyAudio Member
Join Date: Jun 2007

Hi just a guy,
It seems that files cannot be attached to emails generated from this forum. Could you please send me a standard email so that I can reply to you with a copy of the Excel file as an attachment. My email address is given on the Hornresp download website  simply click on my name on the site. Kind regards, David
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8th October 2012, 11:35 AM  #2895 
diyAudio Member
Join Date: Mar 2008

The equation for a Parabola is Y = a.X² + C
We have our two Areas: S1 and S2. From these we can calculate Y1 and Y2. Y1 = SQRT[S1 / PI] Y2 = SQRT[S2 / PI] if we assume that the element starts at 0 and ends at L12 then: X1 = 0 X2 = L12 (Length) a and c can be calculated from: a = [Y2  Y1] / [X2²  X1²] c = Y1  aX1² We can then calculate the area at any point along the segment by Y = a.X² + C S = PI.Y² 
8th October 2012, 02:43 PM  #2896  
diyAudio Member
Join Date: May 2006

Quote:


8th October 2012, 02:48 PM  #2897 
Mark Kravchenko
diyAudio Member

As a followup on the update notification:
Works very well. Still have to figure out what the editor will do. But very interesting. 
8th October 2012, 02:54 PM  #2898  
diyAudio Member
Join Date: May 2006

Quote:
Akabak can't give a detailed list of csa vs length like hornresp can. (If it can I don't know how to do it.) Since Akabak won't do PAR segments, there's no real accurate way for a guy like me (that can barely understand the equations you guys are showing) to lay out an Akabak horn accurately, all you can really do is replace the virtual CON sections with straight boards that create PAR segments in the fold plan. It's been historically proven that this isn't a fatal flaw but it's obviously not the most accurate way. BUT if you can do what I've quoted, but do it with CON sections instead, I could make a spreadsheet that converts an Akabak script (with it's CON segments) to a detailed list of csa vs length like Hornresp does with it's Export wizard. (This mess created by Akabak's non PAR attitude is the main reason I was hoping for more Hornresp segments. But if I can find an accurate way to lay out Akabak's CON sections that's almost as good.) BTW, since this isn't about Hornresp specifically I can start a new thread for this if anyone would prefer that. Last edited by just a guy; 8th October 2012 at 03:12 PM. 

9th October 2012, 06:01 AM  #2899 
diyAudio Member
Join Date: Jun 2007

Hi just a guy,
You've got mail. Kind regards, David
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9th October 2012, 06:54 AM  #2900  
diyAudio Member
Join Date: Jun 2007

Quote:
Further to my earlier post about keeping things in perspective, I think you might find in practice that it really doesn't make much of a difference if multiple parabolic segments or multiple conical segments are used in the simulation model. To illustrate, the attached screenprint compares the SPL response of a tapped horn having three conical segments against the response of the same horn, but with three parabolic segments. You can see that the traces are effectively identical. Greater inaccuracies are already inherent in the predictions due to the assumption that the driver diaphragm acts as a rigid plane piston at all frequencies, and that there are no losses due to panel vibrations, etc. Kind regards, David
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