From the Owners's Manual that I vaguely remember reading when I acquired my EP400s:
Subsonic: Setting this switch to “ON” inserts a 20-Hz cut-off filter in the subwoofer’s bass response to prevent the subwoofer from reproducing frequencies below 20 Hz, which may include rumble from studio air conditioning, subways or other undesirable artifacts. If you play vinyl discs from a turntable, set this switch to “ON” to prevent the subwoofer from reproducing turntable rumble and low-frequency record-warp anomalies.
Leave this switch set to “OFF” for all other digital recordings and DVD sound tracks that contain ultra-deep bass frequencies you want the subwoofer to accurately reproduce.
TAM
