Oh... and you asked about a high-pass filter. My _guess_ is due to port compression and other losses I will never bottom out. With 100w it runs out of Xmax at ~12.5hz.
But I am also ramping up to build a sub-preamp. The crown PS-400 I bought needs a higher voltage then my receiver puts out on the subwoofer output. I also want to use a summing amplifier on the input so I can use the sub with my Tv's default speakers/sound as well. And if I am going to go to all that effort I might as well add a subsonic filter. Elliot Sound has been inspiring me
:
http://sound.westhost.com/