Klipsch RB51 5.25" Reference Series Bookshelf Loudspeaker Pair (Black Ash) Nominal Impedance - 8 Ohms Compatible High Frequency Drivers - 1 (2.54cm) Titanium Diaphragm Compression Driver Mated To 90x60 Square Tractrix Horn High Frequency Crossover - 2000hz Low Frequency Drivers - 5.25 (13.3cm) Cerametallic Cone Woofer Enclosure Type - Bass-Reflex Via Rear-Firing Port