The digital controllers SP 22D and SP 22Ds (subwoofers) have been designed to optimise the overall performance through a dedicated equalisation of each individual speakers. The SP22 D and SP 22 DS are 2-input / 2-output digital signal processors designed to optimize the performance of all QUBE loudspeakers. The SP 22 D, SP 22 DS processors are easily installed in a special plug in port located on the rear panel of a QUBE power amplifier.