I use four in 218 sub complment 6 POL 215 C since 1996 and the system works well trs active, with the processor and amplifier / filter 3v brand Musicson. The 218 sub with these flags back, give a serious good quality with a long porte.Prix purchase trs COMPTITE for a yield lev against major brands. My only regret in the covering collection outdoor flocking trs not adapted to the mobile. I remain a customer of this brand Fidler for all other products.