The P4 passive speakers are full-sounding bookshelf speakers in a satellite-sized package. The goal with P4 was to design a small but powerful bookshelf speaker for people that already have surround receivers or amplifiers and are looking for the same Audio engine sound and quality in a passive loudspeaker. The P4 passive speakers are perfect for digital hybrid amplifiers as well as most stereo receivers, integrated amps, and tube amplifiers. The P4 has a 4 ohm impedance rating but will sound great when connected to almost any receiver or power amp with 4, 6 or 8 ohm speaker output impedance.