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Old 23rd January 2003, 03:44 PM   #1
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Default TQWT Question

Hey all, almost done with my current spk. box project...now it's time to design a TQWT. I have a small understanding of how it works, but still very confused. I have lots of room to play with, so I figured for my first attempt I would like to do this with a "tube" and lay it on the floor (on feet ).

I would think doing this with a tube will be less of a pain than with a folded line type enclosure. My problem is that, although great info on this subject I have found on the net...I still can't get my head around it. First find the Fs and figure out it's 1/4 wave length. But what I don't understand, is what to do next. Do I figure out the "closed/sealed" volume the driver should use, then figure out the volume of what my tube is cut to length of the 1/4 wave? If so, I don't think the resonance of the driver in the air space will equal the length of the tube...(I can play with the stuffing afterwards to tune)

Very confused...any help with this would be fantastic!

Say my driver is an 8" with an Fs of 29Hz, would my tube have to be 1130 (speed of sound)divided by 29 (Fs) = 39ft, 1/4 of that would be 9.74ft....am I on the correct tack?

Rino Odorico
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Old 23rd January 2003, 04:12 PM   #2
kneadle is offline kneadle  United States
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Go here:

http://www.quarter-wave.com/

and here:

http://geocities.com/rbrines1/

The mathcad worksheets on King's website are remarkable, once you get the hang of it, and Brine's has some helpful things to offer with regard to design.


Hope that helps,

Dave
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Old 23rd January 2003, 04:27 PM   #3
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Default ?

Thanks for the quick reply...though I still "don't get it" fully. If I'm building a "pipe" type, should I just find the length I need, attatch the driver and play with the stuffing?

Rino Odorico
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Old 23rd January 2003, 04:40 PM   #4
kneadle is offline kneadle  United States
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Pipe length will have to change. This was something that took me the longest time to "get."

If you tune the thing according to the 1/4 WL of the FS, you'll have the problem of the rest of the harmonic wavelengths causing your pipe to resonate. So, you've got to stuff it. Stuffing it causes something to happen (dunno what, planet10 and MJK will respond further, I hope) so that the resonant bass frequency bottoms out, usually beyond a healthy frequency for your driver.

Thus, the pipe must shorten. You have to sorta work with the equations until the pipe resonance (the very first resulting chart in King's Mathcad worksheets) is reasonable AND the SPL response (a few charts down) is relatively flat.

That's about how my design is going. I'll let you know when I produce an actual enclosure, slated for sometime this weekend.

Dave

PS--design the pipe around the driver before you build.
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Old 23rd January 2003, 05:31 PM   #5
MJK is offline MJK  United States
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Dave has given some very good advice. Look at Bob Brines' site for some practical design advice and a good explanation of what the various parameters in a quarter wave design contribute. His documetation is excellent and should help you get started.

The other key word is "design", if you cut and try you severly limit your chance at producing a high performance speaker. Run the simulations before doing any constructing.

If you want details of the theory behind the simulation (highly unlikely) you can read the theory section on my site.

Hope that helps,
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Old 23rd January 2003, 06:08 PM   #6
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Default Ok, got my figures...I think

Well, I have my sub and the calculations. Going to try this soon. Wish me luck!

Thanks for the replys guys!

Rino Odorico
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Old 23rd January 2003, 07:27 PM   #7
Bose(o) is offline Bose(o)  Canada
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Does anyone know of a calculation for the width of the waveguide. I also found an article stating the area of the waveguide at the beginning and end of the Transmission line, but not sure what the view of the speaker is..cross-sectional side-veiw? Here are the rules that Vance Dickason wrote about...

Sd (1.2 to 1.5)@ beginning=tight bass and lean sound.
Sd(1.5<=)@beginning=Enhanced bass and better mid-bass.
Sd@end of line

The value you get is the area...
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Old 23rd January 2003, 08:36 PM   #8
kneadle is offline kneadle  United States
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Bose(o) Wrote: "Here are the rules that Vance Dickason wrote about...

Sd (1.2 to 1.5)@ beginning=tight bass and lean sound.
Sd(1.5<=)@beginning=Enhanced bass and better mid-bass.
Sd@end of line"

I haven't read Vance Diskason's work, but his assertions are borne out by the experience of Bob Brines, as far as I can tell from his website. Martin King's Mathcad worksheets include this kind of data, and I believe they are represented as a function of some sort.

BTW, Martin, I read your technical worksheets which you mentioned above while I was designing my TL. I had no experience in this type of thing whatsoever, but I found that attempting to understand them was a fruitful discipline in itself. Even if I don't get it, the tech specs you included caused me to ask the right questions.

Dave
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Old 6th February 2003, 02:14 PM   #9
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I done a little study around the TQWT. You can read the complete article on my site, unfortunately it is in italian. sorry, try with babelfish

ciao
Filippo
www.audiofanatic.it
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