QB5 sub, too good to be true? - diyAudio
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Old 19th September 2008, 09:16 AM   #1
Pashley is offline Pashley  Canada
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Default QB5 sub, too good to be true?

I've been looking at an article on qb5 alignments, http://sound.westhost.com/qb5align.htm (excellent site, IMHO)

I'm wondering about applying that to a subwoofer. The basic idea is that you tune the box so there's a hump down low in frequency response, them use eq to smooth it down to the
response you actually want. All the eq is cut so you are reducing some risks which are increased by schemes that use boost (Linkwitz transform & most other bass eq); exceeding either the amp's ability to deliver power or the speaker's excursion limits. Sounds useful.

Looking at tables in the article, it appears there are a couple of "magic" values of Qt where F3<=Fs, around Qt=.32 in Group 1 and Qt=.445 in Group 2.

Parts Express have woofer a selection guide:

Click on any parameter heading to sort by it -- most people would likely look at "sealed F3" and "sealed volume" or the corresponding "vented" numbers.

I sorted on Qts and looked for .32 or so with a low Fs. Lots of possibilities, including some smaller drivers that might work for folk who need a compact sub. I'm not much worried about size, so the one I like is a Pioneer 15 inch

Qts=.32 so F3<=Fs=24 Hz, efficiency is pretty good at 96 Db 1W/1m, and it is only $50.

Box size comes out at around 8 cubic feet, not ideal but not horrible for a 15" woofer. A 2-foot cube or a more-or-less reasonable length of sonotube.

So this isn't a compact sub and any vented vented system gives somewhat poorer transient response than a correctly designed sealed box. I can live with those, unless the transient response really sucks.

Other than that, it looks amazingly good. 24 Hz F3 and 96 Db efficiency with a $50 woofer and dead simple eq. Wow!

What am I missing here? Are there problems I have not noticed?

Has anyone tried something like this? How did it work?
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Old 20th September 2008, 06:34 PM   #2
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Join Date: Oct 2006
Location: San Diego
I read that a few months ago, it's a neat trick. The author makes a good point, that it's ideal for midranges, where the steep rolloff will make it easier to integrate with a sub.
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