Assuming that you have a powered subwoofer, you can improve the bass performance by:  1. Setting the speaker level to remove crackling, hissing and any other undesired sound 2. Removing the distortion - set the amp gain to low, play some music and turn up your receiver’s volume until you hear the distortion. Note where the distortion started because this is the loudest volume setting 3. Flattening the signal 4. Adjusting the subwoofer gain and low-pass filter until you don’t hear any mid and high-frequency sounds