Kuerl Underseat Subwoofers (popular models include the K-1003APR and KP10APR) are ultra-compact, active (powered) subwoofers featuring a built-in amplifier housed inside a slim, cast-aluminum chassis. Measuring only about 2.6 inches (68mm) thick, they are specifically designed to fit directly under a car seat to add deep bass without sacrificing trunk or passenger space.