Spreadsheet for Folded Horn Layouts... - Page 11 - diyAudio
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diyAudio Member

Join Date: Jan 2009
Location: Columbus, Ohio
Quote:
 Originally Posted by Brian Steele I finally got a chance to look at this. Yep, it seems like an error. The height of the back panel was being calculated incorrectly. I did a quick fix (see attached), but came across another minor issue - when you enter dimensions, they're used as external dimensions rather than internal ones (so the external dimensions will be larger in each direction by 2*panel thickness). I've decided to rewrite that section of the workbook anyway, and will upload the complete version when finished (a few weeks, as I'm converting it from a stepped to a continously expanding horn, and including some calculations for bracing).
You KNOW I didn't read this! I just clicked on the attachment.

diyAudio Member

Join Date: Nov 2007
Quote:
 Originally Posted by BP1Fanatic I know I'm being anal, but why is this TQWP not 825.8cm2 (16" x 8") thru the whole 304.80cm (10ft) pipe? Under Initial Parameters, h should = 81.28cm (8" x 4 x 2.54cm). Are those parameters internal or external?
Did you do the optimization routine? D should be 0, not 0.12.

I'm removing the optimization routine from the new version of the spreadsheet, because it leads to confusion. Instead the spreadsheet will spit out the equivalent S1 to S4 parameters for HornResp input.
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diyAudio Member

Join Date: Jan 2009
Location: Columbus, Ohio
h 86.99cm = D -0.10
h 87.01cm = D 0.33
h 87.00cm = D 0.12 = blue TH!

h = 81.28cm = 8" x 4 folds x 2.54cm
w = 40.64cm = 16" x 2.54cm
d = 76.20cm = 2.5ft x 4 folds x 30.48cm(12" x 2.54cm)

Why do you prefer the right fold over the left fold?
Attached Images
 foldjpg.jpg (207.1 KB, 576 views)

 4th December 2012, 04:14 AM #104 diyAudio Member     Join Date: Jan 2009 Location: Columbus, Ohio h 86.995 = D 0.01!
 4th December 2012, 04:19 AM #105 diyAudio Member     Join Date: Jan 2009 Location: Columbus, Ohio h 86.9943 thru 86.9947 = D 0.00!
diyAudio Member

Join Date: Nov 2007
Quote:
 Originally Posted by Brian Steele Did you do the optimization routine? D should be 0, not 0.12. I'm removing the optimization routine from the new version of the spreadsheet, because it leads to confusion. Instead the spreadsheet will spit out the equivalent S1 to S4 parameters for HornResp input.

Well, presenting a new spreadsheet - BOXPLAN-THAM. This spreadsheet allows you to optimize the layout a "THAM" style TH before cutting any wood. The spreadsheet gives you all the panel dimensions required. Basically you enter the parameters for the desired TH, then adjust the panel sizes until predicted result (in blue) is a close match for the "guide" curve.
Attached Files
 boxplan-tham.zip (30.8 KB, 195 views)
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 8th June 2013, 04:13 PM #107 Mark Kravchenko diyAudio Member     Join Date: Jan 2002 Location: Perth Canada It will be interesting to try it out Brian. __________________ Mark www.kravchenko-audio.com
 10th June 2013, 07:47 AM #108 diyAudio Member   Join Date: Aug 2002 Location: luxembourg This one looks realy great.
diyAudio Member

Join Date: Nov 2007

I've attached a spreadsheet that I've put together to assist with designing the layout of THs using a folding technique that's similar to the "SS15" TH design. I used this spreadsheet to design and build a new TH that fits a bit better in my car's trunk and addressed any bugs I came across along the way, so it's pretty much bug-free at this point.

To use:

1. Enter the dimensions of the subwoofer driver in the "Driver Dimensions" table

2. Enter your preferred box dimensions in the "Box Dimensions" table. If you are countersinking the driver (which I strongly suggest for this type of build), use the "driver offset" box to enter how deep the driver is going to be embedded into the baffle. If you're going to mount it on top of the baffle, enter "0" for the driver offset.

3. The spreadsheet models a dual-expansion TH like the SS15. If you want the change in expansion to occur a bit earlier in the horn, enter "x" for the "S3 at 3rd fold" option.

4. Under the "HornResp" params section, enter starting values for S1, S5 and L12.

Now, under the "Horn Design" section, enter the thickness of each panel under the "P" column, then start fiddling around with the horn expansion options and the panel lengths (basically all of the options in blue text). Keep your eye on the "Horn Expansion" graph. Basically your goal is to end up with a horn expansion that is as smooth as possible. The spreadsheet will automatically calculate the parameters that you'll need to enter into HornResp to simulate your TH design. If you don't like the results, adjust the TH layout accordingly, following the process above.

As the process is an iterative one, it may take awhile to come up with something acceptable.

Some notes:

1. The spreadsheet uses the "Advanced Centerline" method to determine the length of the horn. The measured results of the built vs. simmed horn suggest that this method produces results that are accurate to within 3%.

2. The spreadsheet assumes butt-joints and square cuts for all panels. It also does not calculate the dimensions of any braces (I'll add that in a later version). If you want to make angled cuts and use a different joining technique, it shouldn't be that difficult to take the panel dimensions from the spreadsheet and adjust them accordingly. And you'll need to design your own braces.

3. I was a bit skeptical about using 0.5" (12mm) ply for building horns, but it seemed to work out Ok for this test build, with certain conditions, like using stringers to make sure that the ply doesn't end up splitting when screws are being driven into it!

4. From my observations after having built THs for the same driver using two folding techniques, I'd say that the "SS15"-type fold is superior to the THAM-type fold in terms of end results, but the THAM-type fold is easier to build. With the THAM-type fold, a lot of attention needs to be paid to the bracing at the S1 and S3 points to reduce panel flex - much more than in the case of the SS15-type fold. This panel flex can cause the response at the upper end of the TH's passband to sound muddy if it is not properly addressed.
Attached Images
 20131229-phantasmo-1.jpg (242.6 KB, 360 views) 20131230-phantasmo-1.jpg (209.7 KB, 354 views) 20131230-phantasmo-2.jpg (99.0 KB, 340 views)
Attached Files
 boxplan-ss-4-2.zip (59.7 KB, 100 views)
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Mark Kravchenko
diyAudio Member

Join Date: Jan 2002
Quote:
 3. I was a bit skeptical about using 0.5" (12mm) ply for building horns, but it seemed to work out Ok for this test build, with certain conditions, like using stringers to make sure that the ply doesn't end up splitting when screws are being driven into it!
It does work!

And if in doubt you can cut the head off of a finishing nail and leave the pointed side out of the chuck in a drill. Use the nail as a small diameter drill bit to make a pilot hole. IT will definitely not split then.
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www.kravchenko-audio.com

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