I just tried to correct some nulls in the bass (40/50hz)as heard in the listening position by using a sub and a parametric equalizer to supplement mains operating full range (down to 28hz). It didn't flatten (raise) those nulls appreciably, either electronically or by woofer placement without shaking the walls! I may have been sitting in a null but the walls must have been in a node. Compared with results that worked a little bit (less than a 3db change in the nulls) I preferred an amp with a better bass response. FWIW.
