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Old 13th December 2003, 05:24 PM   #11
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Not sure why the photo didn't load. Maybe I'm doing something wrong. I attached it as a file. Does it have to be on line and attached as an image link?
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Old 13th December 2003, 05:26 PM   #12
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I'm on a learning curve guys, bear with me.

Click the image to open in full size.
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Old 13th December 2003, 06:06 PM   #13
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by sreten
http://www.quarter-wave.com/

According to the theory on the above site folding is not a good thing

sreten

http://www.quarter-wave.com/Project02/ML_TQWT.pdf

referring to to the observations on page 9 regarding the straight
and one fold TQWT.

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Old 13th December 2003, 07:00 PM   #14
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Hi Sreten,

I've read the article and agree with the rationale. As noted in previous posts above, this may be more critical in full range TL design than in SW designs. Perhaps I'm wrong, but I haven't come accross any literature that indicates otherwise. A single fold SW would necessitate minimum cabinet lengths of approximatel 6 ft. Not an option for most real world applications!
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Old 13th December 2003, 08:40 PM   #15
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Astro, thanks for the feedback. I will make sure the 3D version has the full list of variables. My intent was to keep it small and make the final calculation easy to do. If a builder has decided on a driver and dimensions for a straight line, then filling in the variables is easy at each bend. The overall volume of the line will be greater, but the equation ensures that the TL length will always be the same.

GM: My original thinking on this comes from playing the sax in my teens. Even then, I knew intuitively that any change in the shape of the waveguide creates a tonal change. By giving the waveform a smooth transition around corners, we lessen the reflections that create the acoustic mess. I think a lot of muddy LF comes from enclosures that bounce around too much energy, creating diffractive effects within.

I agree that using stuffing to limit upper harmonics is good for subs and the theory that the low frequencies have a wavelength too long to make a difference is probably correct for fairly simple waveforms. But even bass notes have tonal qualities and accurate presentation of that tone becomes important. Even a basic 30Hz wave should have harmonics at 60 and 120Hz and these should be presented by the sub (up to the XO frequency). More complex waveforms will have even more that really should not be attenuated more than needed. The stuffing should never attenuate harmonics, just clean up the reflections.

:)ensen
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Old 13th December 2003, 10:56 PM   #16
GM is offline GM  United States
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>referring to to the observations on page 9 regarding the straight
and one fold TQWT.

====

The way I interpret it is he's proving my point WRT the detrimental effect on performance a simple diagonal divider board has in a rectangular cab due to not maintaining the flare rate through the bend(s).

====

>My original thinking on this comes from playing the sax in my teens. Even then, I knew intuitively that any change in the shape of the waveguide creates a tonal change. By giving the waveform a smooth transition around corners, we lessen the reflections that create the acoustic mess. I think a lot of muddy LF comes from enclosures that bounce around too much energy, creating diffractive effects within.

====

Depends on the BW Vs pipe cross sectional area and length.

====

>I agree that using stuffing to limit upper harmonics is good for subs and the theory that the low frequencies have a wavelength too long to make a difference is probably correct for fairly simple waveforms. But even bass notes have tonal qualities and accurate presentation of that tone becomes important. Even a basic 30Hz wave should have harmonics at 60 and 120Hz and these should be presented by the sub (up to the XO frequency). More complex waveforms will have even more that really should not be attenuated more than needed. The stuffing should never attenuate harmonics, just clean up the reflections.

====

Not sure what you mean here. Excepting pipe organs, low frequency music is composed mostly of suppressed fundamentals, so it's their upper harmonic structure that defines their tonal qualities. Since we don't want the increasingly out of phase output of the vent to comb filter with, or modulate, the driver's output or comb filter with the mains, doesn't it seem reasonable to you that damping the out of passband pipe harmonics is required to maintain the proper tonal balance within the passband?

GM
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Old 15th December 2003, 03:21 PM   #17
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Hi guys, any thoughts on the cabinet design? Also, why don't my file attachments show up on the posts. I had to upload the jpg to a website and use img html which can be a PIA.

BTW, thanks to the moderators for letting me post directly! Like most audiofiles, I prefer instant gratification!
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Old 15th December 2003, 10:08 PM   #18
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But I would want a sub to reproduce big pipes. As stated, I haven't yet built my sub, so I have no empirical evidence yet. However, my thinking has always centred around the TL opening allowing the exit of phase corrected backwaves, such that a forward facing "port" would be need to be 180deg from the backwave of the driver. So whatever FR is coming from the front of the driver needs to be duplicated at the port. In an 2-way design, the LF driver may be handling BW up to 3kHz. That means the port should also. Ideally, the stuff should not attenuate the harmonics of a wave since the driver also puts those harmonics out the front. But the interior of the enclosure should prevent internal reflections as these will interact and create acoustic mush which will eventually show up at the port.

What I haven't been able to surmise yet is whether putting the driver right at or near a fold will cause problems with the air being "pumped" in two directions. Like Astro-Muse, every cabinet I've designed so far places the driver at a bend and it worries me. I've tried to move it but doing so forces the design away from MJK's alignment table parameters.

:)ensen.
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Old 15th December 2003, 10:20 PM   #19
sreten is offline sreten  United Kingdom
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Quote:
So whatever FR is coming from the front of the driver needs to be duplicated at the port.
I'm sorry but you appear to have a fundamental misunderstanding
of transmission lines and the way the 1/4 wavelength works, and
the consequences of the 1/3 wavelength, 1/2 wavelength and 1/1
wavelength which are alternatively in and out of phase with the driver.

Replication of the front output of the driver is simply not possible.

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Old 15th December 2003, 10:33 PM   #20
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Default I don't mean to be pesky but...

At the risk of interupting your debate, I'd love to hear some feedback about my original question. Is my design, which requires 6 folds, doomed to fail, or should I go ahead and start cutting wood?
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