| 12Pi v2 [message #51834] |
Mon, 18 February 2008 07:10  |
Roland Gama
Messages: 38
Registered: May 2009
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Baron |
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Hello Wayne,
There seems to be an error with the external panels measurement.
The plans show that the 45 degree cut on the external panels begin at 38-7/32 from the edge of the mouth opening while all other panel cuts makes this one to be 36-3/8 (ie a difference of about 2 inches.) for things to click in place. Am I right?Roland.
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| Re: 12Pi v2 [message #51843 is a reply to message #51842] |
Thu, 21 February 2008 13:53  |
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Wayne Parham
Messages: 18787
Registered: January 2001
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Illuminati (33rd Degree) |
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I had originally thought about making the throat be a long slit, spanning the width of the horn. But the truth is the wavelengths involved are from 10 feet to 40 feet long. So having two 27 sq. inch holes that are 5 inches tall and spaced a foot apart is acoustically the same as one long thin 54 sq. inch hole. It was easier to do and just as good.It's a matter of scale. Since the wavelengths of sound passing through basshorns are large, small features don't matter. That's why you don't need curved flares, exponential/hyperbolic flares can be approximated with a few straight segments. Same thing with mid/tweeter horns, but at a smaller scale. Ever notice the grains in ABS plastic tweeter flares? They're acoustically small compared to the wavelengths passing through the horn. Small features are like grains in film, which are too small to see. If you enlarge a photo enough, you'll see it has grains like pixels of a computer screen. They're just not visible at the scale the photo is used at. This is kind of the same thing with acoustics, if features are small compared to wavelength, they make no difference. Compare the 12π Hornresp models with the measurements. Both are available at the link below. The model describes a perfect horn with a curved flare and a throat at the apex, just like the Hornresp schematic shows. The actual physical horn has four segments and the throat begins with a long thin apex and two square holes cut near it. Even so, the measurements tracked the models extremely well. - 12π hornsub info (scroll down to the sections on development, construction and test results)
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