The Blues BL6.5 has an Fs of 36 Hz in our component set, and easily plays well below 60 Hz at volume with authority. We have NO problems letting them play full range in the demo or competition vehicles, and with the right amp and door re-inforcement they audibly go into the 20 Hz range. If you don't beleive it I suggest you find one of the vehicles at a show near you and hear it. The limiting factor is the actual power output of the amp at low frequency and how much flex the steel door panel has. We are running 200 watts RMS per channel to the component set in my vehicle and never cut the bottom end out of the 6.5 and we play it loud. The 6.5 has nearly 1.25" of total travel, and will not bottom out on the motor structure.