SR series sub-woofer bus system. The SR4719A can be used for indoor and outdoor concerts, as well as for moving speaker systems in halls, concert hall speakers, discos, etc. The SR4726A, SR4731A, SR4732A, SR4732A-T, and SR4733A are also suitable for use in combination with the SR4719A. If you place the SR 200 a horizontally, you can place two of these models vertically.