Features: A passive radiator system uses the sound otherwise trapped in the enclosure to excite a resonance, making it easier for the speaker system to create the deepest pitches. Bass radiator, also known as "drone cone", for replacing the inverted tube or subwoofer with the radiator and the traditional back subwoofer. When air escapes the pipe at high volumes rapidly, air turbulence noise is no longer an issue.No more high frequencies reflected out the port. Passive radiator operates in conjunction with the active driver at low frequencies, sharing the acoustic load and reducing the excursion of the driver. Used to adjust the bass, the designer can adjust the overall tone of the speaker. Package Includes: 2 Pieces Diaphragm Specifications: Material: Rubber Size: 50x90 mm/1.96x3.54 inches Approx. Color: Black note: 1.Please allow slight inaccuracy due to manual measurement, make sure that you do not mind before you order. 2.Due to the difference between different monitors, the picture may not reflect the actual color of the item.