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Old 30th November 2004, 06:59 AM   #1
Cruiser is offline Cruiser  Canada
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Default Critical Q Subwoofer

I got the reference to this project from one of the other threads and was wondering if anyone has built/heard or knows anything about this design. I've been to the website and they seem to be pretty amazing performance wise.

http://members.ozemail.com.au/~joeras/sub_index.htm


I intend to use this as an anchor for a HT/music system using the Vifa XG18/Seas 27TDFC ((John Kritke design).
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Old 30th November 2004, 09:07 PM   #2
Cruiser is offline Cruiser  Canada
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Default Correction

Tthat was John krutke ...was either too late or just typed to fast ....
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Old 1st December 2004, 09:06 PM   #3
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It's a nice subwoofer project, but you can use any quality subwoofer whose box size brings the Qtc to 0.5.

Not that the Peerless is not a good choice-it is.

WinISD, freeware, as well as Subwoofer Simulator, freeware, and a host of others will tell you what size box will give you a Qtc = 0.5 with any driver.

Or you can ask on the board, and someone will tell you.
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Old 2nd December 2004, 02:13 AM   #4
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That particular driver is not really designed for a sealed box. Yes, you can put it in a sealed box and the apply a lot of EQ to it. However, after the EQ, it no longer has Qtc = 0.5, a fact the "Critical Q" designer is apparently unaware of.

There is another design using the same driver in a sealed box with EQ. http://www.linkwitzlab.com/thor-intro.htm
Look into that one. Linkwitz most assuredly knows what he's doing. The box for that one has about twice the volume, which Linkwitz says will "lead to acceptable amplifier power requirements."
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Old 2nd December 2004, 04:16 AM   #5
RHosch is offline RHosch  United States
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There's nothing preventing that driver in a smallish sealed box with EQ from having a Qtc of 0.5. It does require the correct EQ... in fact, the one described by Linkwitz in the link you posted. The penalty for a small box is amplifier power requirements, not Qtc, provided that you know what you are doing with EQ/filter theory.
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Old 2nd December 2004, 05:20 AM   #6
mike.e is offline mike.e  New Zealand
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Quote:
However, after the EQ, it no longer has Qtc = 0.5, a fact the "Critical Q" designer is apparently unaware of.
I think that once some one makes a statement on a website,people take it as being true - until the truth is shown.

I like linkwitz's style- design -> measurements
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Old 2nd December 2004, 06:08 AM   #7
Cruiser is offline Cruiser  Canada
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Keltic,

Thanks for the input, I'm new to all of the calculations, but not to actually building projects. The reason the CQ caught my eye was that it was the first SW project I've seen, that talks about the actual shape of the frequency response and not just about getting low.
I want the final system I build to be better than the last speaker project (and that turned out very good, but was quite awhile ago) and I'm quite content with following what the far more experienced builders/designers have already designed and tested.
I haven't found any other woofer projects that seem as detailed, simple to build and focused on sound quality and not the "HT punch". I was hoping this thread would get enough feedback to push me in the right direction (if I'm not going that way now).
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Old 2nd December 2004, 08:02 AM   #8
mike.e is offline mike.e  New Zealand
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Well if your after fidelity, a horn system, or low Qt value sealed box woofer will be musical.

Make sure that you have enough excursion on the driver you choose so that it is is operating linearly, This is why i dont use sealed boxes myself-Id require several to replace my jbl 2226 BR.

If i head heaps of high excursion drivers id do a dipole,but again,even worse displacement wise-simply cant afford all the drivers,and I dont want shiva quality.

Note that even an F3 of 40hz is 'okay' while 30hz is alot more fun,and ofcourse more better in theory.

A DPL12 can reach 30hz in 2pi with a Qt of 0.7 ,note that it has extremely low Fs,moderate Q and low efficiency- a true sealed box woofer. Ofcourse I wouldnt reccomend just one in a large room if you like it loud.

With a little bit of backround knowledge you can make some choices in order to get the right result.

Cheers!
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Old 2nd December 2004, 05:35 PM   #9
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Quote:
Originally posted by RHosch
There's nothing preventing that driver in a smallish sealed box with EQ from having a Qtc of 0.5. It does require the correct EQ... in fact, the one described by Linkwitz in the link you posted. The penalty for a small box is amplifier power requirements, not Qtc, provided that you know what you are doing with EQ/filter theory.
Yes. Power requirement for the amp, and power handling capacity of the driver.

Maybe I should have said, "potentially changes the Qtc."

A Linkwitz transform could put it back at 0.5 Qtc. But that's not what the Critical Q guy is doing. Linkwitz, on the other hand, presumeably knows a thing or two about a Linkwitz transform.
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Old 2nd December 2004, 05:45 PM   #10
Colin is offline Colin  United Kingdom
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I believe Thor on the full range driver forum (I think he's also on this forum) uses the critical Q subwoofer. I'm not sure whether he modified the design.

Colin
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