Dayton Audio DAEX32U-4 Ultra 32mm Exciter 20W 4 Ohm Heavy-duty design with a 32 mm voice coil for a high 20 watt RMS power handling Pre-applied 3M&#8482; VHB&#8482; adhesive for quick, secure installation Rare-earth neodymium motor and a proprietary two-layer voice coil 4-ohm impedance for use with small, Class D amplifiers