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16th April 2011, 09:00 PM  #1 
diyAudio Member
Join Date: Aug 2006
Location: Copenhagen, Frederiksberg

Calculating 7 section tractrix horn – help!
I have a very specific request for help calculating a 120 Hz trac horn in sections. I am building it myself so I need to assemble it from cutouts since I don’t have access to a lathe. I have heard that J. M. Le Cleac’h’s Excel sheet can do it but I don’t know how to use it properly (keep in mind that I am not an excel geek).
The goal is to get adequate loading from 150 Hz and up to 800 Hz where the horn will hand over to a Coral M 100 driver. I will be switching to a 2” or 1,4 “ driver a some point in the future and dropping the XO to 500 Hz but for now 800 cycles is the goal. So I would hope one of you guys can give some directions for calculating these seven petals/sections using the JML spreadsheet. THanks Kris 
19th April 2011, 09:51 AM  #2 
R.I.P.
Join Date: Oct 2005

Hello,
Here is the coordinates of the points for a (1/2) facet of a 120Hz horn having a 1.4 inch throat. Best regards from Paris, France JeanMichel Le Cléac'h 
19th April 2011, 10:11 AM  #3 
diyAudio Member
Join Date: May 2007

Hej Kris,
Quite a large horn you will build. Don´t quite get if you want to go Le Cléac'h or Tractrix. Also I don´t quite understand what At you want. Anyway this is a program I found somewhere at the Internet. You can check its accuracy by doing a 4petal and compare to Hornresp. Seems complicated, why not build a square, even if round will be better, in 8mm "spårad MDF"? Easier to place anyway. Maybe the MDF will also work with the 7petals. When using two glued against each other it is extremely rigid. http://www.revintage.se/tractrix12.exe Last edited by revintage; 19th April 2011 at 10:22 AM. 
19th April 2011, 04:25 PM  #4 
R.I.P.
Join Date: Oct 2005

Hello revintage,
The 7 facets Le Cléac'h horn (T = 0.707) calculated in message Calculating 7 section tractrix horn – help! is 1.5 meters long if calculated for a 1.4 driver if you stop the mouth at 180° then the diameter of the mouth is 1.20 meters. if you use a complete roll back then the outer diameter is 1.6 meters. Best regards from Paris, France. JeanMichel Le Cléac'h 
19th April 2011, 05:33 PM  #5 
diyAudio Member
Join Date: May 2007

Hello JeanMichel,
I am very familiar with your spreadsheet as I used it when designing the 200T(1m dia) together with Jack. Use them with 2441 and they are great. Due to size of your horn I supposed Tractrix was an option being somewhat shorter and with less Am. But a 180degree/120cm Le Cléac'h would maybe also be managable. 
20th April 2011, 06:45 AM  #6  
diyAudio Member
Join Date: Jun 2007

Quote:
I am pretty sure that the Hornresp figures are correct :). Kind regards, David
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20th April 2011, 07:03 AM  #7 
diyAudio Member
Join Date: May 2007

Me too! Did it differ much? As you do everything so right you have to update to a multipetal version soon.

20th April 2011, 07:34 AM  #8 
diyAudio Member
Join Date: Jun 2007

Hi Lars,
For the example I checked, the Tractrix12 applet calculated the maximum value of x proj to be 115.60 cm. The Hornresp equivalent figure was 112.60 cm. Circular and square / rectangular crosssection options are probably quite enough for Hornresp, for the foreseeable future :). Kind regards, David
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20th April 2011, 10:59 AM  #9 
diyAudio Member
Join Date: May 2007

Agree, square/4petal should be enough and also so much easier to deal with.

22nd April 2011, 08:34 AM  #10 
diyAudio Member
Join Date: Jun 2007

Hornresp Update
Hi Lars,
The Hornresp export horn data tool now has a multiple petal option  3 to 20 sides can be specified. Thanks for suggesting the feature, I just couldn’t resist implementing it :). Product Number 2840110422 refers. Incidentally, I found the error in the Tractrix12 applet  the 'x proj' value gives the length along the curved wall of a circular crosssection horn. It should give the length along the curved petal side wall. Kind regards, David
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www.hornresp.net Last edited by David McBean; 22nd April 2011 at 08:59 AM. 
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