By far, addressing the acoustical behavior of your listening room. Bass modes can result in not just constructive and destructive waves creating peaks and/or troughs in bass response, but also "slow" sounding bass due to the resonant modes created by the rooms' dimensions, which left unaddressed linger long after the speaker has stopped reproducing bass notes. And higher-frequency wall reflections can also lead to the smearing of timing cues in recordings. PRaT = timing.
