The DSP sub is a bandpass box with two small woofers in side. The bottom of the box has about 30 torx screws. These screws become loose after a while and need to be snuged up. Be careful not to put too much torque on the screws as the box is plastic. If you strip a screw I would put some crazy glue on the threads and put it back in the hole. The Stereophile Test CD has worble tones that will allow you to hear the vibration of the bottom panel. Run the subwoofer tests before and after tightening the bottom plate. Good luck... Bill