<<Having designed many filters during my career - just a note: brick wall
filters
<<have large overshoot in the step response. The shaper the filter the more the
<<<overshoot.
Thanks for thinking about this. Not being an engineer I may use terms loosely.
I actually had not realized there are "brick wall" filters which behave just as
you say.
As I understand it, the minidsp does all the filters and crossovers in the
digital domain and the implications of that, I haven't a clue. To prevent the
passive sub from adding so much THD at the lower frequencies,
one can just use the "crossover" tab in the minidsp in the proper channel and
tell it to install a 48 dB/octave filter at the appropriate frequency----it
draws out the filter for you so may have to tweak the freq so it doesn't affect
frequencies that are OK. It is a black box to me, but works well. I haven't
done so yet and need to do that and run a sweep to be sure it does what I
intend.
<<Testing at lower signal levels vs higher levels might be an
<<interesting test. (this assumes I know what you are doing, which I don't
<<fully...)--------- Well
that makes two of us that aren't quite sure. ;-))
REW (very economical software available at AVNirvana) prompts you to check
levels before running the sweeps. It gives a range that is acceptable--to
quiet and the noise floor is too high and too high and things go haywire and
I'd have to wear ear protection. Good point, I'll check the distortion of the
passive sub at a sl lower level too. I read that the distortion at very low
freq is rather tough to discern which is probably why I had not noticed.
>From what I read about integrating two subs with time aligning and EQing to
>create one virtual sub, the math is not normal----1 +1 can equal 0.7. That
>is the whole system may not sound as well if one of the subs is wildly
>different and underperforms. I am seeing a tad of benefit and less seat to
>seat variation likely due to modal averaging. It is really quite
>straightforward---hook up calibrated mic (cheap Umik1 is fine) to laptop,
>minidsp via usb on a extension, and use a long HDMI cable for laptop to the
>AVR. Pick the calibrated mic on the input choice in REW (placed at ear level
>in the MLP--main listening position) and the AVR as output and one can run
>the sweeps. Did I mention REW is free?
Mike
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