With thunderous low-frequency output and extreme deep bass extension, with accuracy and control, the PB-4000 is a benchmark-setting subwoofer on every level with unheard-of performance and features for even double the price. The sophisticated DSP amplifier creates three port tuning modes, each with individual response curves to achieve the most accurate in-room frequency response possible. With the PB-4000, it’s like having three subwoofers in one.