Duypham,
The SMS-1 does 3 or 4 critical things:
1) A very flexible low pass crossover - frequency, slope, phase, & polarity all have very fine dgree of control. Some subs have this type of functinality built-in. Very few have this HIGH DEGREE of functionality. Critically important IMHO.
2) Parametric EQ. When added to the above, you can match the level of the subs to the main w/great precision. You can also choose a crossover frequency where response isn't too "lumpy" & use EQ to smooth whatever humps & dips ther are. This is IMHO critical to seamless x-over.
NOTE: You need a video monitor to take advantage of this. When the readout looks "flat" from the x-over frequency on down, you're pretty much golden. You also use the monitor to help place your subs for smoothest response before applying any EQ - again, very important IMHO.
3) EQ allows you to "fix" major humps and dips in the subwoofers output, without impacting the signal to the mains (if you run those full range or use a different high pass unit).
4) Depending on the sub, the EQ will allow you to boost the lowest frequencies to extend the botom end. I used to own 2 Velodyne 8" SPLRs and this was very important. I now own 2 12" Rythmik subs and this isn't really important at all.
Hope this helps.
Marty
