A really small unit for use in tiny models; selectable 4, 6, 8 or 12 Cylinder diesel engine sound. Adjustable Running and Tick-over rates. Two adjusters for 'character' of sound.1 Watt output. Plugs into the receiver; 'straight-through' connection to the speed controller; both receive their power from the receiver battery. 66mm x 31mm x 20mm. SUPER 2W speaker recommended