Zsound has been paying great attention to create ultra-low frequency loudspeaker, for the LF is the essence of music, and subwoofer is the natural extension for the system. Designing procedures in Zsound include: large numbers of the linearity and non-linearity surveys, constant AES power measurement, detailed computer modeling, complete prototyping, and exhaustive comparative analysis.  And then, the specifically designed OEM procedure can efficiently optimize the available resources of all bandwidth, as well as performance of the whole system. Therefore, S18B subwoofer is the optimal complement and extension for Zsound Loudspeakers.