Cool, thanks CB . I've found I prefer the 2 x 12 setting, the 4 x 12 sounds a bit boxy
It's probably that dip the 2x12 setting takes at 500 Hz (vs. 600 Hz for the 4x12 setting). The dip there seems to 'open up' the mids and adds clarity... think of Fender clean vs Marshall. Fenders typically notch the mids lower than most higher gain amps/cabs... it's part of the 'clear' sound...
The MP-2 2x12 emulation keeps the response down at just past 1 kHz and peaks at just over 2 kHz. That's a classic recipe for clarity.
It's not only that 500 Hz dip, but also that the 4x12 is ~2 dB more up at 200 Hz and ~3 dB up at 300 Hz, which does bring about a decently more voluminous lower body.
While this 2-3 dB difference may not seem that much, still, when combined with the differences in the mid-scoop, it's no wonder that the 4x12 sounds decently darker - despite both emulation rolling of at the same 12 dB/octave and from the same frequency.
I must confess I had expected the high roll-off differences being more pronounced.
Good pspicing! I must get back into such analysis at some point.
Oh BTW, it would be very interesting seeing a phase analysis; you know, how the phase changes over frequency can have significant impact on tone, even if amplitude levels don't change too much.
With this I'm thinking about how the filter circuit changes from 2x12 to 4x12 could produce different phasing characteristics..