they can take up to 2.75 cubes a peice so 5 to 5.25 should be nice for daily id go with 34-37 ive got a hdc3 15 in a 5.5 cubic foot box tuned to 30 and it does very well on music for a daily setup but i tuned it to 30 just for the lows but all around sound at 34-37 is great