The 18-220S 18" Cast Frame Subwoofer Speaker is built to engineering perfection using the most innovative design concepts and materials. B-52 transducers are manufactured to maximum tolerances by some of the most well-respected engineers in the world. All loudspeakers are subjected to a wide array of quality-assurance tests during and post assembly. It"s for these reasons that B-52 speakers typically have a 0.2% return rate and are backed by a five-year warranty.Multi-layer, precision-wound polyamide voice coils create superior electro-mechanical energy conversion Rigid, heat dissipating cast-aluminum or steel frames provide ultimate motor structure support Deep, bumped back plates allow the voice coil to reach maximum excursion without bottoming-out, resulting in deep bass Advanced cone materials with superior internal damping mean ultra-fast transient response and super-low distortion Tough, flexible surround with long-throw, positive-roll design, control extreme cone excursion and is highly tear-resistant Vented pole piece pumps air through the magnetic gap and directly over and around the voice-coil