Under 150-200Hz your ears are often not nearly as important as your body in perceiving the directionality of the “sound.” The reason is that your body can feel the direction of the low frequency waves even though the wavelength is long enough that your ears can’t readily determine the direction. The reason is that as the room grows smaller and the frequency lower that directionality of bass becomes harder to distinguish is that standing waves tend to override the directional waves from the source. Given sufficient acoustical energy low bass directionality in the open is distinguishable at great distances, 20+ miles in some cases. In the old days, when I "was" a grunt, “sound and flash ranging” was a common technique in locating enemy artillery batteries for providing counter battery fire.
In a room the directionality becomes ambiguous because the reflected waves tend to blend with the directional ones confusing ones perception of their directionality. The brain then uses other cues (e.g. higher frequency waves) to determine the directionality of the source of the lower frequencies, an important reason to properly calibrate ones system both for distance and volume.
As Jay says 80Hz is a generalization, and as such is not correct for everyone in every situation, in determining the best crossover frequency. The larger the room, the closer the bass source to the listener, the louder the bass source (relative to the rest of the system), the location of the subwoofer relative to the other bass sources (mostly the mains), the crossover frequency, and ones individual perception (often born of real world experience) all combine to lower the frequency at which the directionality of bass in an enclosed space is perceivable. There is a reason that companies making mid-bass speakers suggest that they be placed near-field it has something to do with Fred’s signature “Physics, It works Bitches!”
