@paradisecom 1++
Subwoofers can not beat the laws of physics. Play a 20 Hz test tone at moderate volume and place your hand on the sub's enclosure. It will be shaking./ Newton's third law. Any shaking or vibration of the enclosure = distortion.
Balanced Force subwoofers place identical drivers on opposite sides of the enclosure operating in phase. The forces generated cancel out and the enclosure remains fixed in space. Any vibration left is cabinet resonance, another significant problem with subwoofers. Balanced Force subs are currently made by Martin Logan, KEF, Magico and me. Me is way too expensive:-) All other subwoofers are fatally flawed including Rels and JL Audio. Eventually they will all come around and use balanced force designs.