Looking for help with a TQWT box - diyAudio
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Old 13th April 2004, 07:34 PM   #1
xbofmnx is offline xbofmnx  United States
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Default Looking for help with a TQWT box

the specs for the speaker I'm tring to configure the box to is:
fs = 20.48 Hz
re = 4 Ohm
lvc = 1.81mH
bl = 12.93
sd = 807.6 cm2
vas = 120.3 Liters
Qes = .39
Qts = .378
Qms = 12.28

I have done some reasearch and i have used the Martin J. King Mathcad TQWT sheet...but im not sure how to use the information I have recieved from it.

The part I think im stuck on is how to tune the box with multiple folds I was thinking like 5 or 6 Folds

any help would be great I have spend the last 2 weeks stressing out over this and the lack of sleep is starting to affect me

thanks,
Brian
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Old 13th April 2004, 11:48 PM   #2
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For what its worth....

Start by looking at Martin's alingment tables at http://www.quarter-wave.com/Theory/Alignment_Tables.pdf
This will give you a rough idea of the length of tube needed. With a driver with a Fs in the low 20's, you will need a long tube. You also need to decide how you want to taper the tube (if at all). I guess the general recommendations going around the forum are 3:1 or more. This will roughly put you around 133 inches for a 20Hz tuning, with the biggest end of the enclosure toward the speaker.

Start puting numbers into the worksheet from there, including driver off-set and stuffing density. I like to make alterations to the box sizing first, then alter the stuffing when I am all done to flatten out the dips and peaks.
As for folding, it is just a nice way of making a smaller box. All in all, the lenght of the tube is what matters. As for folding a tube, you may be able to get away with 2 or 3 folds in a tall skiny box.
If you need a smaller enclosure, consider a mass-loaded design by putting a port at the open (now closed) end. This will allow you to shorten the length, while keeping the response similar.
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Old 14th April 2004, 03:27 AM   #3
GM is offline GM  United States
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Something's fishy, the BL product is only ~half what it should be (I calculate ~24.905), so either the 12.93 is wrong or one or more of the other specs are. What driver is this, and is there any more info available?

GM
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Old 14th April 2004, 04:05 AM   #4
azira is offline azira  United States
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Quote:
Originally posted by random_id

I guess the general recommendations going around the forum are 3:1 or more. This will roughly put you around 133 inches for a 20Hz tuning, with the biggest end of the enclosure toward the speaker.
He wants a TQWT, not a Tapered TL. That means he wants the driver nearer the closed end and the port at the big end.

Bob Brines website has some good starter info for this kind of thing. Do a search on his name in google, it's a geocities website. Scroll down his TOC and look for "Design a TL" It has some rules of thumb for different topologies. For a TQWT you generally want the driver at 50% of the length.

I don't know the other effects of putting a lot of folds in it but consider this. The CSA (cross sectional area) as you go around a fold changes dramatically from a straight pipe. The more folds you put in the less you're likely to hit your target predicted behavior.
--
Danny
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Old 14th April 2004, 04:50 AM   #5
GM is offline GM  United States
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>He wants a TQWT, not a Tapered TL.
====
Hmm, TQWT = tapered quarter wave tube. Isn't this a (reverse) tapered TL? If it was an expanding one it would be a horn.
====
> That means he wants the driver nearer the closed end and the port at the big end.
====
Correct, for a tapered TL.
====
>For a TQWT you generally want the driver at 50% of the length.
====
Well, this is a very general guideline for a positive taper (horn). For max smoothness with a driver best suited for a pipe, it's a function of taper/expansion ratio, with it sliding towards the top as the taper ratio increases, and down towards the mouth in a horn.
====
>I don't know the other effects of putting a lot of folds in it but consider this. The CSA (cross sectional area) as you go around a fold changes dramatically from a straight pipe. The more folds you put in the less you're likely to hit your target predicted behavior.
====
True, though it affects the Fb tuning much less than the upper harmonics, which you want to suppress anyway, so the folds allows you to use less stuffing.

GM
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Old 14th April 2004, 07:13 PM   #6
xbofmnx is offline xbofmnx  United States
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these are the subs im looking at:
http://www.partsexpress.com/pe/pshow...number=295-185

here is a link to there specs:
http://www.partsexpress.com/tech/295-185.html
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Old 14th April 2004, 09:11 PM   #7
GM is offline GM  United States
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OK, for whatever reason you posted some specs for the -185 and others for the -190 and Re as nominal instead of its DCR. If you used these to sim with, I bet you got some interesting results.

Since it's the -185 you really want, then using the DUMAX specs is what I'll use since they are quite a bit different, allowing a considerably smaller cab.

posted:

fs = 20.48 Hz
re = 4 Ohm
lvc = 1.81mH
bl = 12.93
sd = 807.6 cm2
vas = 120.3 Liters
Qes = .39
Qts = .378
Qms = 12.28

295-185:

fs = 21.73 Hz
re = 2.69 Ohm
lvc = 1.81mH
bl = 12.51
sd = 506.7 cm2
vas = 120.3 Liters
Qes = .38
Qts = .369
Qms = 12.53

295-190:

fs = 20.48 Hz
re = 2.6 Ohm
lvc = 1.81mH
bl = 12.93
sd = 807.6 cm2
vas = 280.9 Liters
Qes = .39
Qts = .378
Qms = 12.28

295-185 DUMAX:

fs = 21.17 Hz
re = 2.7216 Ohm
lvc = 1.81mH
bl = 13.1097
sd = 464 cm2
vas = 96.2719 Liters
Qes = .3731
Qts = .3536
Qms = 6.7645
Xmax = 16.44mm


I assume this is for music and since the Fs is low enough, then tuning it to ~16Hz for organ pipes seems the obvious choice, so right off the bat it's obvious that there's not much quality performance to be had with this driver in a TQWT since its Vas and Qts is too low for the requisite pipe length.

A shorter straight ML-TL OTOH looks much better and its Fb and Q can be easily adjusted by shortening the vent length and vent damping:

L = 74.47"
So/SL = 74.71"^2 (net)
Density = 0.2 lbs/ft^3
rp = 1.75"
Lp = 18"
Xo = 24.06"

It's compact enough to stand it up in a corner or lay it down along the wall or fold it in half.

GM
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Old 14th April 2004, 09:23 PM   #8
xbofmnx is offline xbofmnx  United States
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HAHA thanks for pointing that out i was looking at the wrong specs when i posted the stats

thanks but what does this actually mean?
L = 74.47"
So/SL = 74.71"^2 (net)
Density = 0.2 lbs/ft^3
rp = 1.75"
Lp = 18"
Xo = 24.06"

74.47 is trhe lenthg of the cabinet?
whats the width and depth?
whats the port opening size if i was to use a slot port?
plus what would it be with out any filler?
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Old 14th April 2004, 09:37 PM   #9
GM is offline GM  United States
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>thanks but what does this actually mean?
L = 74.47"
So/SL = 74.71"^2 (net)
Density = 0.2 lbs/ft^3
rp = 1.75"
Lp = 18"
Xo = 24.06"
====
You've been using MJK's program and haven't bothered to read his application notes that explains all this?
====
>74.47 is trhe lenthg of the cabinet?
====
Yes, inside dim.
====
>whats the width and depth?
====
Whatever works. Obviously, since the cross sectional area (So/SL) is little more than Sd, a rectangular shape will be required to get the driver to fit.
====
>whats the port opening size if i was to use a slot port?
====
Depends on its width. I don't recommend using a >9:1 ratio, but it's academic since the vent needs to be longer than either the cab's width or depth.
====
>plus what would it be with out any filler?
====
Hollow sounding.

GM
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