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Old 3rd November 2011, 11:07 PM   #11
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Join Date: May 2010
Location: was Chicago IL, now Long Beach CA
For one driver:
Qtc .38 3.9 cubic feet
Qtc .4 3.4 cubic feet
Qtc .45 2.5 cubic feet
Qtc .47 2.23 cubic feet
Qtc .48 2.12 cubic feet
Qtc .49 2 cubic feet
Qtc .505 1.8 cubic feet
Qtc .6 1.255 cubic feet
Qtc .707 .85 cubic feet

Last edited by cyclecamper; 3rd November 2011 at 11:24 PM.
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Old 3rd November 2011, 11:19 PM   #12
sreten is offline sreten  United Kingdom
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Hi,

Download WiniSDpro (free) for excursion, power handling etc.

You can scale whatever your using to see low response, i.e. setting
Fs x 5 will show a response of 20 to 500Hz equal to 4 to 100Hz.

rgds, sreten.
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Old 3rd November 2011, 11:26 PM   #13
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Boxes are larger than I thought.

So I'm guessing if I mount (adjusting the box volume for the space occupied by the speaker(s):
1 driver in the cabinet it's about 2.2 cubic feet, Q just below .48
2 pairs of 2 clamshelled drivers in two holes in the cabinet it's a similar 2 cubic feet, Q around .49
2 clamshelled drivers in one hole in the cabinet, it's equivalent to 4.4 cubic feet, ridiculaous Q around .38
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Old 3rd November 2011, 11:27 PM   #14
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sreten, so where can I get it and will it run on Vista, as my XP machine is down.
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Old 3rd November 2011, 11:42 PM   #15
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So, I don't care about the -3db point but
Qtc .38 down 14.61db at 20 hz, down 10.26 db at 30 hz
Qtc .49 down 16.49db at 20 hz, down 11 db at 30 hz

Doubling the box size it's a little teensie bit better output below 40 hz, but any noticeable improvement is below 25 hz, if it can make the excursion.
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Old 3rd November 2011, 11:46 PM   #16
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This isn't going to go very low with the stock woofers. Maybe I should look at adding mass to the cones and lowering Fs. So I can measure the new Fs easily enough, but how do I calculate the new Vas and Qts from the old numbers?
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Old 4th November 2011, 12:19 AM   #17
sreten is offline sreten  United Kingdom
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Hi,

2 pairs per cabinet clamshelled will down low with room gain.

LinearTeam

You can add further EQ, a lot easier than cone mass adjustment,
but TBH critically damped boxes (Q= <0.5) should sound very good.

Having researched this, commercial subwoofers go very low at modest
levels, with bass boost, but back off the boost as you approach the
excursion limits of the drivers, to prevent overexcursion.
These adaptive circuits are common commercially, but not in DIY.

Line level passive EQ bass boost is very simple for Q=0.5 boxes.
see : Baffle Step Compensation
but think 30Hz rather than 300Hz as the centre frequency. Lowering
the lower resistor will increase maximum relative bass boost available.

Though a better solution (in max SPL respects and perceived extension at the limits)
might be a peaking high pass filter set to Q = 2 to 3 set to as low as you want to go.

rgds, sreten.

Might as well point out the drivers with such a low Q are not really suited
to sealed or isobaric ideally, and individually vented very low in boxes you
would end up with a monstrous low end capability, lots of big boxes though.
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When your only tool is a hammer, every problem looks like a nail - Abraham Maslow

Last edited by sreten; 4th November 2011 at 12:43 AM.
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Old 14th November 2011, 09:00 PM   #18
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Well, I didn't make the best choices but practical ones. I'm stuffing 4 (2 clamshelled pairs) into each box for Q .5 with a brace installed. It's not going to go as low as a tapped horn could, but with 4 boxes that's still 8 12" drivers exposed to room air and they have acceptable xmax, so it's going to make plenty of bass in the more-perceived range. If I want more lower, I might get some more of the same cabinet kits and load them up with 2 15's clam-shelled isobaric in each. Yes, big ported boxes would have a lower -3db point. But I'd hoping these put out something detectable even lower. I will see soon enough. Few more weekends of construction. I sure wish I hadn't sold my table saw.

Last edited by cyclecamper; 14th November 2011 at 09:03 PM.
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