Calculating 7 section tractrix horn – help!

[hasselbaink]

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

[Jmmlc]

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

Jean-Michel Le Cléac'h

[revintage]

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 4-petal 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 7-petals. When using two glued against each other it is extremely rigid.

http://www.revintage.se/tractrix12.exe

[Jmmlc]

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.

Jean-Michel Le Cléac'h

[revintage]

Hello Jean-Michel,
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.

[David McBean]

Originally Posted by revintage

You can check its accuracy by doing a 4-petal and compare to Hornresp.

The 'x proj' values seem to be a little different to those calculated by Hornresp for a 4-petal tractrix horn.

I am pretty sure that the Hornresp figures are correct :-).

Kind regards,

David

[revintage]

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

[David McBean]

Hi Lars,

Originally Posted by revintage

Did it differ much?

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.

Originally Posted by revintage

You have to update to a multi-petal version soon.

Circular and square / rectangular cross-section options are probably quite enough for Hornresp, for the foreseeable future :-).

Kind regards,

David

[revintage]

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

[David McBean]

Originally Posted by revintage

You have to update to a multi-petal version soon.

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 2840-110422 refers.

Incidentally, I found the error in the Tractrix12 applet - the 'x proj' value gives the length along the curved wall of a circular cross-section horn. It should give the length along the curved petal side wall.

Kind regards,

David