Soundstream BX-20Z Digital Bass Reconstruction Processor Digital Bass Driver with Dash Mount Remote Bass Control Bass restoration circuit accurately recreates and injects low frequency information back into the signal path Bass equalization circuit contours the restored bass to your speaker subwoofers Bass maximizer indicator has 2 LED Indicators that flashes when the bass maximization circuit is activated PFM Subsonic filter switch to protect your subwoofers and fine tune the bass response of any system