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In Reply to: RE: Terms and examples please posted by Bill Fitzmaurice on March 27, 2021 at 11:21:15
Practical is a matter of definition. That I need my truck to go get the bits is about as bad as it gets. Space to hang 14-15' is not an issue either... :)
A bit of guidance on the notch at the discharge end would still be most welcome.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
Follow Ups:
The discharge end is called the terminus. I have no idea what you mean by the notch, or by 'de-comb'. A tube is not a good method of constructing a transmission line, which should be tapered for best results. It also makes mounting the driver difficult, as it is typically located 1/5 the way down the pipe.
I think we perhaps are contemplating different things. I am looking at something like El Pipo. Woofer at one of a quarter wave( of minimum freq ) long tube. Comes on at when L=Lambda/4, then Lambda/2, then 3Lambda/4 and Lambda...yes? Goes off in the middle of these patches also. The comb response. They de-combed El Pipo with stuffing. Would rather go wid the 'notch'.I have seen these done in smaller scale on an Altec compression driver, with a notch cut out of the terminus end that was I think some sort of exponential curve tapering back towards the driver. I am not clear on just what is following this profile...area of *something, width of the slot? Or what?
So what sort of profile, and how far down the tube should the thin wedge of the notch start? as in what sort of exponent on a per length?
Given the 'feel' I think about 1/3 of the length will do...with the width exponentially growing towards the discharge end. Exponent chosen to get to at least 90% of half the circumference at the chosen length.
cheers,
Douglas
so half width of the slot, from 0 to L/3( of 15')=e^.09032*x
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
Edits: 03/27/21
I vaguely remember the El Pipo, but it was so forgettable that I didn't give it much notice when it came out, even though I was a contributing editor at AudioXpress at the time. I thought it odd that they'd make something that didn't improve upon the acoustical labyrinth described by Harry Olson in 'Elements of Acoustical Engineering' in 1940, especially considering that George Augsperger's definitive work on TLs was published a year before the El Pipo. What you refer to 'de-comb' with stuffing is actually suppression of pipe harmonics, which dates to 1965 by A.R. Bailey. It has nothing to do with comb filtering.
If I could find a set of sim software that had an acceptable learning curve I'd probably ask fewer questions.
"What you refer to 'de-comb' with stuffing is actually suppression of pipe harmonics, which dates to 1965 by A.R. Bailey. It has nothing to do with comb filtering."
Suppression of the pipe harmonics as you put it, and it having 'nothing to do with comb filtering' does not quite square with what I see going on. It looks like a semantics issue to me, which is no doubt why the sim software gives me such fits...
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
For there to be comb filtering there must be two distinct sources operating in the same pass band placed at least 1/2 wavelength apart. That's not the case with a TL. What is seen with the terminus output of an un-stuffed TL is resonant peaks and dips. That's not comb filtering. It resembles comb filtering on an axial SPL chart, but the peaks and valleys with comb filtering vary with the listening position. They're a constant with a TL.
Edits: 03/28/21
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