SVS PB4000 Subwoofer 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 its like having three subwoofers in one.