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Old 27th November 2007, 11:31 AM   #1
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Default Vas and TQWT

Hello,
This is my first post on this forum !
I want to build a TQWT using Fostex 167e (I already have one with 103e, that is really musical but a bit on the light side).
I prefer when my speakers are not to big (so does my wife)
Does anyone has an idea concerning the relationship between global volume of a TQWT and VAS (Vas of Fe167e is 35,94L)? should it be under or above it ? what influence on speaker behavior ?
Thanks in advance,
Eric (France)
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Old 27th November 2007, 12:20 PM   #2
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http://www.quarter-wave.com/Theory/Alignment_Tables.pdf
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Old 27th November 2007, 03:59 PM   #3
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quite a hard stuff to read...and understand
eric
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Old 27th November 2007, 04:07 PM   #4
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That's because there isn't really a simple solution unfortunately.

If you make the cabinet too small, then the LF will roll-off due to the lack of sufficient Vb.

If you want a relatively compact cabinet, I'm not sure why you want a TQWT? A simple, untapered MLTL will tend to give better results for a less complicated build. Like the attached plans for the FE167E MLTLs that I happen to be listening to at the moment actually. And no -it's not a BR cabinet.
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File Type: gif fe167e mltl.gif (71.5 KB, 456 views)
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Old 27th November 2007, 04:47 PM   #5
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Scottmoose, what is the dashed lines going about half way up the cabinet? Do you have a response curve for this?
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Old 27th November 2007, 06:40 PM   #6
Svein_B is offline Svein_B  Norway
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If you plan to build with the FE167e you should also have a look at Bob Braines site. Even if you do not buy any of his kits or plans, there is a lot of useful information there.

http://www.geocities.com/rbrines1/Products.html
Have a look at Product/ FT-1600 MkII in particular.

SveinB.
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Old 27th November 2007, 08:55 PM   #7
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The dotted line indicates the inside of the baffle material. It's basically similar to Bob's FT1600 MLTL with a few of my own twists.

FR plot? Modelled response:
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Old 27th November 2007, 09:01 PM   #8
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And this is the measured response in Clio. Below ~400Hz the room messes things up, so don't take it too seriously.

I could have made it a little smoother, but I wanted to try & get a little more dynamic impact with this one. Everything's a trade off.
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Old 27th November 2007, 09:02 PM   #9
GM is offline GM  United States
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Quote:
Originally posted by Scottmoose
That's because there isn't really a simple solution unfortunately.
Well, yes, and no, or I would still be fumbling around trying to find a "simple" math solution to calcing BIBs. Messrs Thiele and Small did all the hard math parts though and Messrs Margolis and Small simplified it even further to Vb = 20*Vas*Qts^3.3, so for the BIB all I did was adjust the exponent based on another fact that I can't explain any more than how they arrived at the constant '20', which is that if you leave the exponent the same and multiply Vas in ft^3 times the ~28.217 liter conversion factor you get a Vb that works quite well for any combination I've ever tried. Since the BIBs tend to be too large for most folks, I went back and shorted it a bit figuring they wouldn't be stuffed nearly as much as a typical TL.

Anyway, using the BIB's Vb = 20*Vas*Qts^1.25 will get you one that once stuffed may sound a bit 'thin' without plenty of BSC and Vb = 20*Vas*Qts^1.1707 a bit more tonally balanced for a given stuffing density and get rid of the exponent altogether for a nice 'phat' sounding pipe that may not require any BSC. Note that I haven't compared these to MJK's or Rick Shultz's calcs which no doubt are more mathematically correct, so I present these more as a small insight as to how little Vas affects pipe design since you want its Vb to 'swamp' it and for those folks that don't use either of these WSs for whatever reason, but want to dabble in TL design.

GM
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Old 27th November 2007, 09:05 PM   #10
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Interesting. Cheers as ever Greg.
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