Yamaha A15W
Gives your system big bottom. 
The A15W Subwoofer is the perfect piece to make your A Series system complete. Features a 15" woofer, recessed side handles, black carpet covering, and both a Speakon and 1/4" input connector. 

Yamaha A15W 15" Subwoofer Features: 

Bass reflex, front ported cab
Recessed handles
Black carpet covering
15" woofer
Speakon and 1/4" input

Yamaha A15W 15" Subwoofer Specifications: 

Bass reflex type
15" LF speaker cone 
Frequency Range: 50Hz-200kHz 
Power Capacity: 500W program; 800W peak
Nominal Impedance: 8 Sensitivity: 97dB SPL (1W, 1m)/127dB SPL (MAX) 
Input Connectors: Phone jack ? 2 
Dimension: 19-1/8"W ? 24-1/2"H ? 19-1/8"D 
Weight: 46.1 Ibs.