Wayne Parham Messages: 18792 Registered: January 2001
Illuminati (33rd Degree)
The posted measurements are for the fully upgraded models, but the differences in response aren't major. The benefit of upgraded midwoofer drivers is mostly reduced distortion because the upgraded drivers have shorting rings.
That's not the case with the tweeter compression drivers - they don't have shorting rings - but the biggest differences are in the top octave and are easy to see when comparing the individual drivers. Below 10kHz, they're very similar.
As for bass response and subs, I always suggest flanking subs be used. Both the three Pi and four Pi speakers provide powerful midbass, but neither reach the bottom octave and both benefit from flanking subs. The things you get from flanking subs are not just added extension but also baffle step compensation and SBIR mitigation. It provides much better in-room response than any full-range main speaker with built-in woofer, no matter how deep the response goes.
To be able to provide that benefit, the flanking sub must be placed offset in all three planes - slightly behind, below and beside the main speaker it is flanking. That is what gives it the ability to smooth the SBIR notches from nearest boundaries.