MB>2.  The lowpass output of the decoder has an Fc of 400HZ and there are lo
MB>of directional clues coming from the sub - what is the best Fc to use and
MB>how do I do this  - at line level (before the amp) or at speaker level?
        Well, in my experience, I would say that the best way is to cut
off before the amp (that is, if it is being used ONLY on the sub) so
that the amp sees only those freqs below the cutoff point.  This will
make the amp run easier.  I am more of a pro-audio person so when I
hear the term "sub-woofer", I immediately think "below 125Hz".  More and
more home systems are employing techniques that the pro-audio field has
used for years.  When I think of sub-woofer, I think of something that
is crossed over at no higher than 125Hz and whose real "hump" is from
about 50-63Hz.  Those directional clues are because of the high cutoff.
400Hz is damn near A-440, which if you don't know, is the open 5th
string (2nd lowest) on a guitar and is definitely a directional freq.
The lowpass output could actually be more accurately termed "midpass",
though a true midpass filter would probably have a second cutoff point
in the area of 1.25-2.5kHz.
        Anyway, my suggestion would be to cutoff before the amp.  In
your situation, I would say no higher than 200Hz, but lower if possible.
        Hope this helps...
        Kurt
 * SLMR 2.1a * I think, therfore I think I am.  I think.
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