Dayton Audio DAEX25Q-4 Quad Feet 25mm Exciter 20W 4 Ohm Unique, four arm design for exciting a large surface Pre-applied 3M&#8482; VHB&#8482; adhesive for quick, secure installation Rare-earth neodymium motor and a proprietary voice coil 4-ohm impedance for use with small, Class D amplifiers 20 watt RMS power handling for high output