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Discussion Starter · #1 ·
I have received a lot of questions on how I fold horns in Sketch-Up. This is the way I set out to create an enclosure from a Hornresp sim. It is not the easiest, or the best, but it works. The same basic steps will work in any other CAD/2d design software as well.


First off, after you are happy with the horn click Calculate, and go to the Schematic screen. There you want to export the horn profile.



Now you select the Width of the horn by changing the Height column. (yeah, it's funny that way.) Set the Increments to something like what is shown. You could also change it to 20s & 30 to have less work. Set the Width Flare to Uni, to output a horn with straight sides.



It will create a TXT file that looks like this.


All you are worried with here is the Length, and the Width columns.
 
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Discussion Starter · #2 ·
Now open up SketchUp, and copy the TXT info into it like this. The length is left to right, and the width is up and down here.


The three line going down are the ends of the four horn sections. You need them to line up the front and rear taps later. The middle one isn't really necessary, but I thought it may help here.



Now, connect all the lines, and add a layer of wood around the horn. You will also want to go back, and draw in the centerline from segment to segment.



At this time you want to get the dimensions of the driver itself, and draw it on to make sure there is room for it.


EDIT:I forgot to add that there is a way to help speed the folding process up when you are first starting out.


At his point you can/could/should print the straight horn out. Make it as big as possible on the sheet of paper.


Now there are two ways to do the next part. The fast version is to cut the horn along the many segment lines from the outside edges to the center. Leaving a small area not cut. The slower way is to lay the horn down, and cut all the way across the horn with a razor. Then glue a piece of string along the center line.


The idea is to try out a bunch of different folds with the paper horn. This way you don't spend an hour or two fooling around with it in the computer. Just use some tape, or push pins to hold it down at the corners.


Since you used the segmented model, it is easy to the transpose it back into SketchUp.


If you are trying to hit a certain exterior dimension, add a square of the target size over/under the horn, and print that out as well. Now you just try to get the horn to fit in it's confines.
 

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Discussion Starter · #3 ·
When it is time to start folding you will get to see how good you are at SketchUp.



The easy way to start is to snip the throat area off, and move it over into position with the rear tap.




Now you can add the first bend. Start by adding in a few more segment lines at the new front end of the horn.



Then you take them piece by piece to add in the bend, making sure to align them at the centerline edges.



There are two ways to do this. The way shown here is to tilt the pieces so that the middle of the wooden pieces at the bend all touch the same spot. The second way to do it is to line up the forward corners. The former seems to work best on the smaller bends, and the latter on larger ones for me anyway.



You can see in the last pic that I then add guides to mark the exterior position after the first bends on a wall to make sure I hit the same point with all following bends.


Here is a close up of the next bend. It shows both corner techniques. It also shows that you try and over lap the wood on the sides of the horns. You don't just copy the white area, or the white area and one side.



The white horn area overlap isn't a problem as it it now in the empty area between the segments. It contains this doubled area plus a little more. This way the total horn path area is accounted for.



If you are not trying to hit a set size, and you get to the end and there is a gap where the horn sections will not meet up you need to make the horn wider, or try a different folding pattern. If you have left over sections, you need a new fold, or you need to make the horn narrower.
 

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Discussion Starter · #4 ·
Here is a finished product.


These are the same horn just folded differently. There was a restricted space requirement in all three directions, and that is why the gaps are there. Adjusting the fold to get rid of them would push one dimension or another out of the set limits.


You can clearly see bellow how I go from the the ruff in to the finale plans.

Copy the ruff in, and paste it next to the original. Then remove all unnecessary lines.


Then draw in another version using the spacial info from the last.


 
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Discussion Starter · #5 ·
home base
 

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WOW that is awesome!
 

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Discussion Starter · #8 ·
It isn't my design. I just showed some folding options with it.



It was shoe-horned into the space the drivers owner had here. Several attempts were made by different people. I was trying to figure out how to explain the folding from a Hornresp sim, and this popped out.
 

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Very nice how-to. Thanks for sharing.


My approach is a bit different, as I've got somewhat better Excel skills than Sketchup skills.


I fold similarly to the method first demonstrated by maxmercy, I work with the entire flare sections as a "group" within sketchup, then chop them up and piece things together again. I throw a little Excel in there to calculate the amount I trim off of the flare at each bend to account for the growth through a turn. Nothing more than a little bit of trigonometry here, and it is not perfect, but it is pretty close. I use math based on the method Soho54 showed over in my Shiva thread.


90 degrees = 0.7071*the width at the boundary = amount cut off the length

180 degrees = 1.4142*the width at the boundary = amount cut off the length


Unfortunately, I still do trial and error folding, I thought I had an approach that determined the height given a baffle height and fold width, but that turned out to be a dead end (so far), and it only works for a single topology. Trial and error eventually works, but it is not quick! My last fold took three evenings of attempts, and I was working with 4 (yeah 4) boards internally.


Sometimes simple isn't.
 

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The Mal-X 18" is a pretty decent TH woofer, but likes a big ol' box. I haven't really done any serious modeling with it yet, simply because at the frequencies I'd want to set the low corner at, I'm not sure TH alignment is really the most practical way to go.

Quote:
Originally Posted by lilmike /forum/post/19597920


Unfortunately, I still do trial and error folding

As do I. I try to calculate as close as possible how much length to add to the horn to compensate for my inevitable length errors. Then, I fold, check length, fix step errors, and simulate over and over again until I get something I like.


I may be graduating to this method. It looks much easier in the long run.
 

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Quote:
Originally Posted by soho54 /forum/post/19596620


It isn't my design. I just showed some folding options with it.



It was shoe-horned into the space the drivers owner had here. Several attempts were made by different people. I was trying to figure out how to explain the folding from a Hornresp sim, and this popped out.

Shoot that last fold up looks nice. Not a lot of dead space in there. Is that the one sim all folded up? I hope it gets built by someone.


What is the final dimensions on that haus?
 

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Discussion Starter · #13 ·
They both actually have the same amount of wasted space, and clock in around ~856l total.


Both attempts were made to fit into his very constrained space requirements, and the width is the key factor.


The examples are of your design, completely finished, and the skp files are posted in the original thread. The first here is ~56.5" x 44" x 21"

The second is ~53.5" x 46.5" x 21"


You could shrink the second one some by taking the longest section, and removing the upper corner waveguide. Then calculating the area the horn should take up in that section, and altering the depth to digitize that one section, and retain the correct volume of air. ~53.5" x 45.5" x 21" would be close just eyeballing it.



The first could have the dead space decreased by increasing the height, or you could flip the first few folds around. Either would also shrink the depth as well.
 

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sorry for the totally beginner question but i have messed around with sketchup and i am not very good with it


how did you import the txt file?


when i try to open files with sketchup it either trys to open a .skp or if i try to open a txt file it gives me a popup saying this is not a sketchup file
 

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Discussion Starter · #15 ·
I didn't import it. I just used the information in the txt to draw in the initial skeletal framework in SketchUp.


I have looked into creating a converter, but it is a PITA.
 

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Thanks for the great tutorial SoHo. I've been fuddling around in sketchup, getting pretty frustrated a couple of times. I noticed a couple of things:


While interpolating the length of the bend by rotating and positioning the cut segments is brilliant, I end up throwing the cut segments away in the final drawing.


I've been using a method that might be similar to what LilMike described above. The arc length between the two straight segments being joined by the bend should give you the horn length represented by the bend itself. Then you can just cut the length of the bend off the horn and save it off somewhere away from your model to maintain the proper overall length.


You can do this with math: Arc Length = 2pi * radius * Angle/360 where the radius is half your horn width at the bend and the angle is in degrees (usually ~90 or ~ 180). Arc length is the bend length.


Or you can draw two lines across the mouths (width) of the horn segments to be joined then draw a circle with a center point where the two boards would meet (say at 90 degrees) at the bend. Make sure the circle intersects the midpoints of the two horn segments. Click on the segment of the circle that represents the path of your bend choose "Entity Info" and read the "Length". Then trim that off your horn path:




It saves you the time of cutting rotating and positioning the segments to represent the bend.
 

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Discussion Starter · #17 ·
That method can be made to work with subs, but the key there is to keep the cross sectional volume correct at the right distance.


This is a big problem with a lot of internet horns from not to long ago, and some continue to mess up this way. At least most have stopped blaming the simulators as the problem.
 

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"This is a big problem with a lot of internet horns from not to long ago, and some continue to mess up this way."


does it really make a difference if there is no expansion through the 180 degree bend? i would think the larger problem is modelling the 180 degree bend effects, not minor changes in flare rate along the path.


can you recall one or two horns that were considered a "fail" for this reason? i can't.
 

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Discussion Starter · #19 ·

Quote:
Originally Posted by LTD02 /forum/post/20817852


does it really make a difference if there is no expansion through the 180 degree bend?

It does if it isn't in your model that way.

Quote:
Originally Posted by LTD02 /forum/post/20817852


i would think the larger problem is modelling the 180 degree bend effects, not minor changes in flare rate along the path.

The effects of a single 180deg bend can be molded. The effects of several are harder as they increase in numbers. The new mini chambers tweak things a little in the upper bandwidth.


Don't think of it as flare rate changes, it is horn volume changes that cause the damages. You cut large amounts of volume out of what the horn simulation is expecting.

Quote:
Originally Posted by LTD02 /forum/post/20817852


can you recall one or two horns that were considered a "fail" for this reason? i can't.

Yes, but I'm not going to name names. I have provided several corrected simulations (in open forums and PMs) to older popular horns over the years to people who have built them, and thought something was wrong with theirs when they measured them.


You can try it out yourself easily(well sort easily
) in HR. Sim a jam up single flare three section horn in HR, and then convert it into a four section one. Now reduce S3 and move it up and down the horn between S2 and S4. Depending on where the constriction is it can have a very detrimental effect on the output FR.
 

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"You can try it out yourself easily (well sort easily) in HR."


that is what led to my question. whenever i insert a small section and then make a minor change in volume (going from a constant rate of expansion to no expansion for the small section), i don't see any material change in the frequency response. it's all minor 0.5 db or less so stuff. that is why your comment about it being a "big" problem got me confused.
 
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