I have M3ti front speakers, VP50 center channel, and Athena AS-C2 bookshelves as rear channels. I just bought a Hsu VTF-2 sub. All of this is hooked up to a semi-crummy JVC 8010 "home theatre" receiver. It 's working fine (and sounds pretty darned good) but with the addition of the sub I'm getting frustrated with the JVC's rather limited bass management.
On the JVC, one can set a crossover point (80, 100, or 120 Hz) and set each of the front, rear, and center speakers to "small" or "large". After some testing, it appears to be the case that "small" means "highpassed at chosen crossover point" and "large" means "main speaker unfiltered; bass below crossover point lowpassed to subwoofer".
I used an Avia test DVD, primarily the low-frequency-sweep tone (descends from 200Hz to 20Hz), to try to set the subwoofer level and crossover point. The Hsu subwoofer also has a built-in crossover (low-pass to the sub only; no high-pass output) which I ended up not using.
The best I managed to do was to set the JVC's crossover point to 80Hz and the front speakers to "large". With it set that way, I still don't get particularly flat response. At 200Hz I measure about 75dB; between 100 and 130Hz there's a bit of a hole (level drops to about 69dB) which I think is due to books on shelves about 1 foot behind the M3s soaking up energy in that frequency range (does that make any sense?) and then between about 60Hz and 90Hz there's a pronounced *increase* in volume, with the peak reading around 85dB (!) somewhere around 70Hz. I assume this is because both the M3 and the Hsu are quite good at reproducing sounds in the 60-90Hz range. Below about 50Hz amplitude falls off again, dropping to around 63dB at 20Hz (but this is below the claimed low-frequency limit of the Hsu). At 40Hz, things have fallen off a bit (down to about 68dB) but not so badly.
Thinking about this problem (20dB variance in levels) it seems to me that what I really need to do is filter the M3s somewhere around 70Hz with a crossover with fairly shallow slope, and then re-adjust the subwoofer levels. Unfortunately, setting the front channels to "small" and relying on the JVC's bass management doesn't work well; I get a response curve with a few pronounced dips in it (in particular, the 130Hz-100Hz dip now extends a bit lower and is more noticeable) and a very obvious transition between the sub and the main speakers. I also think I need to get those books out from behind the M3s, assuming that that really is what's responsible for the dip in the curve between 100-130Hz...
It's actually surprising just how good the system sounds now, even with the big dip at 100-130Hz and the big peak at 60-80Hz! It sounds good enough that I intend to double-check with another SPL meter before tweaking anything; but still, the 60-80Hz peak is pretty obvious even just to my ears, with the test tone playing.
Does filtering the main channels with a separate filter sound like the way to go here? It doesn't seem to me there's any good to be had from using the Hsu's built-in lowpass crossover, is there? I considered paralleling the Hsu to the main channel outputs, telling the receiver it didn't have a sub, and setting the Hsu crossover to 60-70Hz, but that still leaves a bunch of wasted energy shaking the M3's cabinets for no real reason at the really low frequencies. Also, does it sound plausible that those bookshelves could be causing the dip at 100Hz?
Assuming filtering the M3s is the way to go, can anyone recommend a good passive crossover that would do what I need? Given that the total cost of my system is in the $1500 range I am not looking for anything exotic or fancy. :-)
