B Series comes in three different models: 

B15  Subwoofer with single 15 inch driver, specially designed for small venues, allows flexible installation with small size.

B18  Subwoofer with single 18 inch driver, specially designed for medium venues, provides strong power and impactful bass.

B28  Subwoofer with double 18 inch drivers has been specially designed for large venues, providing deep and powerful bass with compact design.