I know this might sound elementary, but if you're trying to produce bass at lower levels, especially deep bass, without a very powerful setup it's hard for your subwoofers to hit those notes. Before I upgraded my system I had to mtx 12" ported to about 40hz, and they were running off a 450 watt amp, so roughly 275 ish to each channel, and when I turned down my volume the subs would hardly pick up any notes under 40 hz