it depends on what you want spl or sq and what you have to power it but since you have a bandpass i'm assuming it's for spl. so a rockford hx2 would have great spl maybe an re se would be a better all around sub or a jl 10w3 or a kicker l7 would be another good spl sub but i would recommend using a ported box because i used to run 2 12's in a bandpass then switched to ported and it still gets as loud as a bandpass but has better sq.