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<Two Sheets, 43Hz Folded Horn
<Two Sheets, 43Hz Folded Horn
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Old 24th January 2018, 03:44 AM   #31
StainlessSteve is offline StainlessSteve  United States
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Wow, great idea. The results are barely any different! I definitely don't want the box to be made with L45.
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Old 30th January 2018, 05:23 PM   #32
StainlessSteve is offline StainlessSteve  United States
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If someone can at least help show me how to fold it, here is the input section of the parameters I want to use:
Click the image to open in full size.
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Old 31st January 2018, 08:10 AM   #33
chris661 is offline chris661  United Kingdom
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Steve,

With those parameters, your horn won't do what you want it to do.

You've simulated 135v RMS input, and you're allowing the unit to reach Xmech. It'll sound bad, but not for long - that's a lot of power input, and the driver will burn quickly if subject to those power levels for anything other than very brief periods.
I hit Xmech a couple of times on a nice 15" subwoofer driver, and the cone folded. This was under extreme testing conditions - a ported box driven a couple of octaves below tuning with high power sine waves.
I don't think anyone else here would ever design a cabinet that has to hit the driver's Xmech to live up to specs. Xmax or Xvar (for B&C drivers) is the one to use.

When it comes to folding difficult shapes, my recommendation would be to draw the expansion out on paper, and then cut out each section and re-arrange the sections until you've got something that works.
It was recommended that you keep the final expansion, but have it flat-packed or whatever so you can construct it and bolt it to the original horn. Leaving it out will lose you output and LF extension.

Chris

Last edited by chris661; 31st January 2018 at 08:14 AM.
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Old 31st January 2018, 03:30 PM   #34
StainlessSteve is offline StainlessSteve  United States
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Xmech (86.23v) is 6dB above my requirement and doesn't reach thermal. The voltage input is irrelevant. And S4 is larger by 882 liters and only gets me +2.2dB from 44hz to 133hz.

Last edited by StainlessSteve; 31st January 2018 at 03:57 PM.
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Old 1st February 2018, 02:08 AM   #35
wg_ski is offline wg_ski  United States
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S4 is at the mouth, and S3 is at the back corner. L23 goes up the back, and L12 gets folded back over, possibly multiple times, until you reach S1. Where to include the bends (as part of which segment) depends on where they fall. It will take trial and error. You may or may not end up with an outer box that works well - and may or may not be efficient in terms of wood usage.

If you approach it from the angle of letting the break points between segments be flexible, you can force it into a given box (provided its big enough). Let S3 be at the back corner of a known dimension. Force both ends of the bend to fall directly on the curve of the ideal hyp/exp expansion, following the "advanced centerline". Do the same for S2 at the top rear. The lengths of these segments and thru the bends form L34 and L23. If you run out of space to fit L12 and the driver chambers you need a bigger box. If there is wasted space it can be shrunk. It will take several paper iterations to optimize.

For an offset driver, you have one extra segment to the back short (hyp/exp expansion starts at S2). Now you see why I prefer a 3 segment approximation. OD's are easier to build, but with S1 = 108 it may be a bit iffy with a box of these dimensions. Keeping the outer walls parallel all the way to S1 may or may not be possible. Part of L12 may have to expand in x and the other expand in Y. For a box width close to the driver diameter one direction usually works (say width=21 or 24 inch with an 18 inch driver). It would get awfully narrow with a 12.

If you really want to build this you will need to spend some time playing with it on paper and drawing it out on a 4x4 piece of cheap plywood. I keep a bunch of cheap 3/8 inch on hand just for laying out horns - and I keep the ones I end up using so I have a template to build more later.
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Old 1st February 2018, 02:18 AM   #36
Brian Steele is offline Brian Steele  Grenada
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Quote:
Originally Posted by wg_ski View Post
If you really want to build this you will need to spend some time playing with it on paper and drawing it out on a 4x4 piece of cheap plywood.
...or map it out in a spreadsheet and use Excel's Goal Seek routines to provide the optimum results

If you can provide a sketch of what you're talking about, I might be able to fit an Excel workbook to it, similar to what I've done for the other horn folds at The Subwoofer DIY Page - Horn Folding
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Old 11th July 2018, 01:56 AM   #37
StainlessSteve is offline StainlessSteve  United States
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So I managed to shrink it by 75.25 liters without shifting or lowering the output at the LF corner at all.
Click the image to open in full size.
Comparison at xmax to a single lab horn, which is 697 liters (both at power max):
Click the image to open in full size.

Last edited by StainlessSteve; 11th July 2018 at 02:06 AM.
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Old 12th July 2018, 05:13 PM   #38
StainlessSteve is offline StainlessSteve  United States
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Actually, here's a little more accurate sim of the Lab Horn. Grey line is without HPF:
Click the image to open in full size.

Last edited by StainlessSteve; 12th July 2018 at 05:20 PM.
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Old 17th July 2018, 07:54 PM   #39
StainlessSteve is offline StainlessSteve  United States
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My only concern is the group delay being above the 1.5 cycle audible threshold at 46hz. Grey line is with the shrunken mouth, black is without: Click the image to open in full size.
I imagine the only way to get rid of this while keeping a low volume is to utilize all 4 segments.
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