my personal favorite myth:
15s have more low end than 10s.
response:
the frequency response of a speaker cabinet is a function of system engineering and not cone are. in the olden days people used to believe that because a 15 had a larger cone than a single 10 it had to have lower frequency response than 10s. in the world of real science we know that frequency response is a function of displacement, or the movement of air, which is dependent upon excursion, cone area, and cabinet design, and not simply cone area. this old trope neglected that a 4x10 cabinet has more cone area than a 1x15, and they are typically voiced with a mid scoop, which means more low end response.
the cabinet market now prioritizes portability, and has expanded to 12s and 8s, both as woofers.