What factors might account for a difference in the auditory acuity between the two ears?

Answer 1

A lot of things I suppose.

First of all, the sinuses of your head and face all connect to the middle ear. So if you have a sinus infection or congestion that effects one side more than the other, its possible to have loss of hearing in one ear but not the other. Also, ear wax or anything that clogs one ear but not the other would have a similar effect.

You could also have damage to the apparati of one ear but not the other. There are a lot of structures that can be damaged in the ear; the tympanic membrane, the middle ear bones, as well as the structures of the inner ear, such as the cochlea or the sensitve 'hair' cells that do the actual transmission of vibration into nervous impulses.

Finally, the impulses from the ear to the brain travel on the 8th cranial nerve, called the vestibulocochlear nerve. Obviously, there are two, a right and left nerve to the right and left ears. One could be weaker than the other, perhaps due to some kind of lesion or tumor, or perhaps just a congenital defect.

I guess there could also be abnormalities in the hearing acuity centers of the brain itself, only on one side.

That's all I can think of; most likely it has to do with blocked sinuses due to congestion or a wax plug.

Answer 2

Amount of ear wax.

Integrity of the tympanic membranes for each of the respective ears.

Possible injury to the eustachian tube.