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 12th August 2010, 08:33 PM #11 diyAudio Member     Join Date: Jan 2009 Location: Columbus, Ohio How about an IF/THEN Statement: Blue = [{Vol (1) = Vol (2)} + balance = 0.00]?
diyAudio Member

Join Date: Nov 2007
Quote:
 Originally Posted by soho54 When you say "centerline" do you mean right angles through the corners? If so, this will always be a little long, and the horn will play shorter.
I used that approach.

I also measured using arcs around the corners, and present that in the spreadsheet as L'.

I've also included the srqt method in the spreadsheet. Interestingly enough, the answer it gives is usually within a few mm of the centerline method.

diyAudio Member

Join Date: Dec 2005
Location: Georgia
Quote:
 Originally Posted by Brian Steele I've also included the srqt method in the spreadsheet. Interestingly enough, the answer it gives is usually within a few mm of the centerline method.
Hmm... something seems off. EDIT: I read this wrong.

Here is a picture with a bend made up of three 25cm squares, and the lengths derived from the most popular methods, and my own in the middle.

The Square-root method comes in at 70.71.

Try running this through your program to see what it comes up with.

Last edited by soho54; 12th August 2010 at 09:22 PM.

diyAudio Member

Join Date: Nov 2007
Quote:
 Originally Posted by BP1Fanatic How about an IF/THEN Statement: Blue = [{Vol (1) = Vol (2)} + balance = 0.00]?
Vol (1) is calculated using S1, S4 and L, and it's not dependent on any of the measurements of the box, so it's somewhat misleading at this point.

I'll adjust the spreadsheet to reflect the correct net volume of the box.

"balance" is the difference in height between the front and back of the box, using the calculated values for the folded horn's dimensions in the box. For the box to actually be a box, it should be zero. This is where Excel's "Goal Seek" function comes in handy .

 12th August 2010, 09:23 PM #15 Mark Kravchenko diyAudio Member     Join Date: Jan 2002 Location: Perth Canada Hi Brian Home early from work with a tummy ache. But a whole lot oh gingerale and I'm getting better. Been playing with the spreadsheet. Boy am I stupid. It finally dawned on me that the thickness of the material is in cm not mm. Now the folds make sense. Still have not quite figured out the goal seek function. I found it but hell if I know how to make it work. But fiddle with the box sizes enough and I get pretty close to the desired sizes. I have to say cool. And I have to agree that from a viewpoint of your math skills the descrepancy you described earlier is significant. A real life box rarely measures as modeled. It is always close. But I'm guessing you want to get as close as is posible. Mark __________________ Mark www.kravchenko-audio.com
 12th August 2010, 09:27 PM #16 diyAudio Member   Join Date: Dec 2005 Location: Georgia Did you ever throw your TH model into AkAback to see if the p or c constants used in HR were the reason for your 3Hz measurement difference?
 12th August 2010, 09:36 PM #17 Mark Kravchenko diyAudio Member     Join Date: Jan 2002 Location: Perth Canada I have been reading the thread. As Brian pointed out the method of measureing down the middle of the bends is one of the most accurate means of determining horn path length when it is folded. That is what I have used for years. I tried a front loaded horn that is obviously tappered. I can't get the crazy thing to behave. My deviation from error is small but it don't look like a horn to me! I even used the as built sizes. I'll check what I did again and see if there are any obvious mistakes. I have a couple of ideas for labeling the cells so it is a bit easier to Mark Mark __________________ Mark www.kravchenko-audio.com
diyAudio Member

Join Date: Nov 2007
Quote:
 Originally Posted by soho54 Did you ever throw your TH model into AkAback to see if the p or c constants used in HR were the reason for your 3Hz measurement difference?
No, not yet. I'm an absolute noob wrt Akabak.

 12th August 2010, 09:48 PM #19 Mark Kravchenko diyAudio Member     Join Date: Jan 2002 Location: Perth Canada From David McBean he is actually gone past AkaBak in computaional accuracy. His programis just a bit more limited. I can attest to it's acuracy as can Brian. It is really close to what you will measure in the real world if you actually make the box well. Mark __________________ Mark www.kravchenko-audio.com
diyAudio Member

Join Date: Nov 2007
Quote:
 Originally Posted by mwmkravchenko I tried a front loaded horn that is obviously tappered. I can't get the crazy thing to behave.
LOL - that probably wouldn't work. The spreadsheet can only model the layout of the folded TH as illustrated in the graph, as that's the only one I can mathematically describe at the moment (I really have to spend some time and show the position of the driver in the TH!).

Once I can work out other foldings, I'll include them in the spreadsheet.

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