Filter Filters Harmony Audio 18" Remove All Filters Price $500 and above (2) Condition New (2) 2x Harmony HA-ML181 Monolith 18" Competition SPL Sub 3500W Dual 1 Ohm Subwoofer $724.99 4x Harmony HA-ML182 Monolith 18" Competition SPL Sub 3500W Dual 2 Ohm Subwoofer $1420.99