Hi Riker,
At this very minute, I'm editing and re-writing the manuals for the EP400, 500, 600 and 800. Sorry you got a hybrid version of the EP500 manual and thanks for pointing out the discrepancies in the diagram and text.
If Brent called it a "low-pass filter", he's incorrect. It's very confusing, but a subsonic filter is a high-pass filter (the easy way to remember it is, 'passes the highs, rolls off the lows'). The subsonic filter kicks in at 20 Hz and is useful for filtering out all kinds of garbage below that frequency that may be on older master tapes--studio or hall air conditioning rumble, mike stand noises, etc.--as well as turntable rumble frequencies and tonearm/cartridge record-warp frequencies that will cause all kinds of woofer flapping, wasting power.
Cheers,
Alan
