The Sub-Rock is used for additional power handling of bass frequencies when higher sound pressure levels are needed for improved performance. Has dual 10 inch 4 ohm woofers rated at 250 watts power handling. 180 Hz low-pass filter. Shown in RiverRock Gray. Dimensions: W22xD20xH21. 93db spl 1watt/meter (35hz-180hz). Free ground shipping within the Continental US. Lifetime factory warranty. At last, a way to enjoy incredibly deep bass sound reproduction outdoors. Enjoy music in your patio or garden with the same sound quality found only in high-end indoor speakers. Makes a perfect addition to existing outdoor speaker installations. Completely weatherproof for year-round use. Note: This is a passive sub, NOT powered. It requires a sub amplifier to to gain full benefit from it.