As I mentioned earlier, to get the best bass extension, we need to do a little tweaking to the subwoofer amplifier. For most applications where the low-pass crossover is desired to be below 100 Hz, I recommend enabling the notch filter jumper that is located near the center top edge of the sub amp's preamp board. This jumper will turn on a notch filter that is centered around 55 Hz and about 5 dB deep. This is helpful for eliminating a humped response that is a result of the acoustic high-pass and electronic low-pass fi lters operating in close proximity.

To get the maximum extension at the low end, we can use the parametric EQ built into the amp. From experimentation, I found that having the EQ frequency set to about 22 Hz, the Q set to about .3, and the boost gain set to the maximum will provide an anechoically flat response down to about 27 Hz. To achieve my desired high-frequency crossover point of 80 Hz, I found that the crossover knob should be set at about the 10:00 position. We have to remember that the acoustic cutoff is very dependent on the EQ settings and the frequency response of the woofer itself, and in most cases will end up somewhere between the lowest 30 Hz setting and the midway point of 105 Hz.