"Cult of the Infinitely Baffled"
IB Subwoofer (aka IB subs)

The Adire Shiva White paper talks about an IB sub being 4 times Vas, and says that's where Qts = Qtc. 

If we run the numbers to calculate the closest reasonable box volume where Qts = Qtc, we need to increase the box size to 25 times Vas. With a box volume 25 times the Vas, then the Qts and Fs will be raised only by a factor of 1.02.  One can safely say at this point Qts = Qtc. 

Now a volume of 25 times Vas is impractical for most people's installations, as a compromise we use 10 times Vas as our baseline.....

Note that the 10 times Vas although recommended isn't etched in stone. Why?  Well even the smaller 4 times Vas volume IB, will have better SQ as compared to a standard small sealed box. This is a function of there being less 'box' induced colorations. 

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