As I understand it, the Rubber Soul stereo mix was an odd experiment gone awry. A Hard Days Night, Beatles For Sale and Help! -- all of which preceded Rubber Soul -- have more conventional stereo mixes with the lead vocals in the center and the instruments panned left and right. So it wasn't simply a matter of inexperienced primitive stereo mixing, but rather was a conscious decision.
The thought process behind the hard left/right mix of Rubber Soul with nothing in the middle was apparently an experiment such that when folks with mono eqpt played the stereo LP, the mix would folddown to mono with the levels still balanced (any l/r info in a folddown becomes 3db quieter in comparison with center channel info). In addition, many stereo consoles back then had the speakers close together so this may have been to accomodate that eqpt as well.
I guess they were worried about stereo/mono compatibility or something and they were trying out a different approach. However it makes little sense that someone with mono eqpt would have paid the extra money for the stereo LP. But not every experiment is done based upon sound logic, I suppose.
The thought process behind the hard left/right mix of Rubber Soul with nothing in the middle was apparently an experiment such that when folks with mono eqpt played the stereo LP, the mix would folddown to mono with the levels still balanced (any l/r info in a folddown becomes 3db quieter in comparison with center channel info). In addition, many stereo consoles back then had the speakers close together so this may have been to accomodate that eqpt as well.
I guess they were worried about stereo/mono compatibility or something and they were trying out a different approach. However it makes little sense that someone with mono eqpt would have paid the extra money for the stereo LP. But not every experiment is done based upon sound logic, I suppose.