when you put a driver in a speaker cabinet, there comes a point where bass starts to go not only forward, but backwards. If that driver were in a wall, the backwards wave would simply be reflected forward leading to an even bass response between the forward waves and the multidirectional waves.
In a speaker cabinet, as soon as the baffle of the speaker isn't a "wall", you get a loss of lower bass. You're supposed to compensate for that by "toning down" higher frequencies above where the wave goes behind the speaker in order to equalize everything. If you don't, you get speakers that sound anemic in bass response relative to everything else, and because of that, TLS guy thinks people run their subs hot.
Which i disagree with to an extent... people just like overemphasized bass.