A flat subwoofer is provided comprising a driver in which a coil is arranged in an air gap in the driver, which coil is connected to a membrane, where the driver is arranged on a chassis, wherein the membrane comprises two interconnected parts, a forward membrane part and rear membrane part, where both membrane parts are substantially symmetrical around an axis perpendicular to the membranes plane, where each membrane part has an outer and an inner periphery where the forward membrane part along an outer periphery is connected to the chassis by a surround, and where the rear membrane part is connected to a spring member which spring member at least partly surrounds the driver.