This is what I have put just behind the seat.
£140 on eBay, £180 in the shops
In Phase USW10 features
    * Maximum Power Output 300W
    * Rated Power Uotput 100W
    * Output Impedance 4 Ohm + 4 Ohm
    * Crossover Frequency 50-100Hz
    * Size: 270mm (diameter), 69mm (height)
    * Weight (inc accessories) 4.8kg
    * Phase Button (0-180 degrees)
    * Remote level Control (5m)
    * Aluminium Cone
    * Ultra Slim Design
    * Die Cast Aluminium Chassis
