Tractrix/Volvotreter - help needed

[damkel]

Hi

I would like to try and build a mid range horn. With some help from Google I found out that a Tractrix horn could be a good choice. I found the excel sheet at Volvotreter, choosed Rectangular horn, put in the numbers, downloaded a trial version of AutoCAD and printed the three templates.

By now I was sure I would have understood why there is three templates. I don't get it...

I would have thought there would be a template for the sides and one for the top/button, but no...
I can also see that the sidewall is longer then the frontview/center?

Can someone please explain to this noob how exactly I use these templates?

 

[AllenB]

Does the cross section come out to rectangular? (This might explain why one dimension has longer walls.) At steps reaching straight outward the cross section is specified where the area follows the wanted expansion to make this tractrix (as it will be at lower frequencies). This is also allowing different directing of higher frequencies by setting the shape in one dimension and the expansion in the other.

 

[damkel]

I am sorry Allan but I don't understand your answer.
I have three templates:
1. Frontview
2. Center
3. Sidewall

I think the width of the horn is linear so I made a template of the width of the horn and here the length of the sidewall template is the same as the sides of the width template.
That makes sense, I think

I would have expected the center template to have the same length as the middle of my width template, but it is way to short. The same goes for the frontview template which is a bit longer than the center template.

I feel a bit stupid here but I just can't see how to use the frontview and center templates?

 

[damkel]

Another funny thing is that as far as I can see the diagram in excel is not the same as what is transferred to Autocad?

To me, the ones in the diagram in Excel looks more correct so I think I will try to plot that into Autocad and print it to see what it looks like.

 

[AllenB]

That would be interesting.

 

[damkel]

Well if you know the tv series NCIS you will know what I mean when I say I deserve a "Gibbs" - if not, it's just a wack on the back of your head.

I somehow confused myself with the width template so that should have been the width had become the dept so the horn became to deep and to narrow.
Now I got it right and that helped...

But I still can't figure out what the frontview template is for, but with the sidewalls and center template I should be able to make the horn as far as I can see.