folding a horn

[anomalous]

wondering about the correct way to fold a horn.
my thought would be to take a line down the middle of the horn, pick the point to fold, then pivot around that point, like this:



This would seem to me to be the best way to preserve the length, but ive seen other people do it differently as well. is there a 'correct' way to do it?

Same question for 180 degree folds.

if there is a reference/guide/explanation somewhere on line - please point me at it.

cheers

Ben

[Bas Gooiker]

Folding the horn

There several methods to fold a horn. When you know your way in CAD you can use this CAD-based script.

Another way described on the web (still looking for the source) is to draw the horn on paper and cut it into small rectangular bits. The rectangular bits can than be used to form the folding, based upon a drawing of the inner dimensions of the cab. This (and the next) method will show a path length slightly different from the practical path length because the path length in a corner isn't truely axial, however the difference isn't spectaculair.

Personally I find it easiest to draw the cab in a simple drawing program like MS Paint, using a grid. Before that it was the old paper and pencil/pen. Other digital options are Inventor, Sketch up, CAD or Solid Works.
If you have pre decided on the measurements the cab is going to have, it's a matter of making a side view with height and depth. Using the export function in the schematic diagram gives a list of horn area, width, height, etc. per cm of horn length. Determine the height at S1, S2, etc. by dividing the horn area by the inner width of the cabinet. Alternatively use the inner width as the height.
Based upon this data you can draw the horn starting at the mouth all the way to the (inner) back of the cabinet.
In case of a 90 degree bend there is a horn area just before the bend and a horn area just after the bend, the latter usually smaller than the horn area before the bend (seen from mouth to throat). The horn path within the bend is the axial horn path length and equals half the height before the bend + half the height after the bend.

Now it’s time to take an educated guess: At 41 cm from the mouth (so 41 cm from the throat) the height is 19.8 cm. Directly after the bend the height is now 16.4 cm. The axial horn path length in the corner is 0.5 x (19.8 + 16.4) = ~18 cm. The height of 16.4 cm corresponds to an horn path length of 23 cm (41 – 18) seen from the throat.
According to Hornresp the height at 23 cm should be

At 46 cm from the mouth ( 39 cm from the throat) the height is 19 cm. Directly after the bend the height is now 14.4 cm. The axial horn path length in the corner is 0.5 x (19 + 14.4) = ~ 17 cm. The height of 14.4 cm corresponds to an horn path length of 22 cm (39 – 17) seen from the throat.
According to Hornresp this is correct.

Footnote: A 180 degree bend can be seen as 2 times a 90 degree bend as it follows the same guidelines.

This is a small part of the thread as can be found here: Kickstart Hornresp and Guide to WinISD & Hornresp and Folding horns in AutoCad

[anomalous]

I've seen that article, and a whole bunch of others. all of them were more or less "well, here's how I do it and it works for me" - which is fine, but having now sat down and messed around with both bits of cut out paper, and drawings in CAD, a lot of these methods yield quite different results, and none of them really satisfied me.

Bill? how do you do your bends?

[Bill Fitzmaurice]

Bill? how do you do your bends?

I have my own methods. I don't reveal them.

[anomalous]

I have my own methods. I don't reveal them.

ok, fair enough. can you answer whether they were something you worked out theoretically/mathematically, or by trial and error? (or some combo of both)?

cheers

Ben

[Bill Fitzmaurice]

I have my own methods. I don't reveal them.

ok, fair enough. can you answer whether they were something you worked out theoretically/mathematically, or by trial and error? (or some combo of both)?

cheers

Ben

A combination of both, which demands using Sketchup and HornResp in unison. There's actually quite a bit of leeway in what you can do, but you must check it every step along the way.

[bitSmasher]

You could always reverse engineer to learn... take a 3d model and make it 2d

[Tom Smit]

[quote="bitSmasher"]You could always reverse engineer to learn... take a 3d model and make it 2d

[David Raehn]

I gues that would be called a 'euthanised euphonium'