Tweeter CD wave guide
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Audiodidakt
diyAudio Member

Join Date: Nov 2005
Location: Norway
Tweeter CD wave guide

Robert C White / Rod Elliot have a DIY wave guide design instruction here:

Practical DIY Waveguides - Part 1

(part 2 and 3 of the guide is linked at the bottom)

I have tried to work the formulas into an Excel-spread sheet using the 1500 Hz example in part three, but cannot get the formulas/numbers right: I do not get the same numbers as White / Elliot:

Quote:
 If we make angle α = 90° ... c = ( 720 + 90 ) / 5 = 162 b = 360 - 324 + 90 = 126 W = 1 / 3 * (( 25,306 (126 * 162 + 90 * 162 + 90 * 126 )) / ( 1500 * 90 * 126 * 162) = 142mm The horn radius is... R = ( W - t / 2 ) / sin ( α / 2 ) ... where t is throat diameter and α is the radiation angle. Throat diameter is determined by the tweeter used, and must be measured carefully. The overall depth is ... d = R - (Tan a / 2) ( w - t / 2 ) The radius at points x is ... r ( x ) = ( t / 2 + ( w - t ) / 2 ) - ( R² - ( m + d - x )² ) ½ ... where m = Tan α / 2 ( 0.5w - 0.5t ) and t = throat diameter. x is the centreline distance along the waveguide from the throat in millimetres. x R x R x R x R 0 18.5 6 25.2 12 34 18 47 1 19.5 7 26.5 13 35.7 19 50 2 20.6 8 27.8 14 37.6 20 54 3 21.7 9 29.2 15 39.7 21 59 4 22.8 10 30.7 16 42 22 71 5 23.9 11 32.3 17 44 Table 1 - Offset (x) for various values of R
Are the formulas above incorrect, or do I just have to look more into my excel-formulas? I get the numbers corret to "w" (expect I get 0,1418 istead of 142), but after that White / Elliot do not sum the formulas for R, d and r(x), so I do not know in which formula (R, d og r(x)) my mistake(s) are.

Have anyone made a spread-sheet for designing CD wave guide / Cd horn?

Best regards

Gisle

 26th December 2012, 01:08 PM #2 Ed LaFontaine   diyAudio Member     Join Date: Feb 2004 Location: where the Appalachians rise from the Blue Grass I can provide you with one of a variety of waveguide worksheets that are available. Can you open an excel spreadsheet? If yes, pm your e-mail address to me and I'll forward it to you. This one is based upon Geddes' oblate spheroid profile. __________________ ...call me Ed...Special Ed... EnABL kit http://www.diyaudio.com/forums/swap-meet/119852-enabl-kit.html DCB1 parts http://www.diyaudio.com/forums/swap-...ml#post2361098 Last edited by Ed LaFontaine; 26th December 2012 at 01:10 PM.
 26th December 2012, 10:00 PM #3 DogStar   diyAudio Member   Join Date: Mar 2011 I think your "mistake" is the number 25,306. In your spreadsheet you should use the number 25306. Notice that in the US they don't use the comma the same way as we do in Scandinavia (or many other European countries). Apart from this detail, your computation looks ok. The following formula (in Excel) gives you the number directly in mm: = 1000*(1/3)*((25306*(126*162+90*162+90*126))/(1500*90*126*162)) Good luck with the number crunching. Cheers David Last edited by DogStar; 26th December 2012 at 10:06 PM.
Audiodidakt
diyAudio Member

Join Date: Nov 2005
Location: Norway
Quote:
 Originally Posted by DogStar I think your "mistake" is the number 25,306. In your spreadsheet you should use the number 25306. Notice that in the US they don't use the comma the same way as we do in Scandinavia (or many other European countries). Apart from this detail, your computation looks ok. The following formula (in Excel) gives you the number directly in mm: = 1000*(1/3)*((25306*(126*162+90*162+90*126))/(1500*90*126*162)) Good luck with the number crunching. Cheers David

Aha! Suddenly I blushed... Thanks!

And also thanks to Ed for email.

 27th December 2012, 11:54 AM #5 Ed LaFontaine   diyAudio Member     Join Date: Feb 2004 Location: where the Appalachians rise from the Blue Grass In case you are not aware of his work, Dave Pellegrene is thermo-forming waveguides. acoustic waveguides http://techtalk.parts-express.com/sh...ght=pellegrene __________________ ...call me Ed...Special Ed... EnABL kit http://www.diyaudio.com/forums/swap-meet/119852-enabl-kit.html DCB1 parts http://www.diyaudio.com/forums/swap-...ml#post2361098 Last edited by Ed LaFontaine; 27th December 2012 at 12:00 PM.

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