Preliminary tests on the first prototype B12 subwoofer show 2nd harmonic distortion reduction beyond -10dB at frequencies above 150Hz. But to get a reduction of distortion at frequencies below that requires a larger shorting ring.Small shorting rings are suitable for midwoofers, since midbass and midrange performance is improved. But to get distortion improvements at subwoofer frequencies requires a larger ring.
A design that uses a shorting ring outside the coil has already been proposed which would allow larger shorting rings to be used. There may be other alternatives too. So I've asked Eminence to consider this an open project, and to go ahead with development of the second prototype. I'm told it may take a few months.