For the ear (a) and (b) the speakers 1 and 2 do not present the same distance from one another, we can metaphorically with the term holography in physics transpose it in listening experience where we use the ear (a) and the brain computing indirect sound wave (b) and direct soundwave (a) alternatively and reciprocally (as the light wave of reference in an hologram ) from the reference wave incoming from speakers 1 and speakers 2 by a time differential delay ( the interference pattern in physics) different for each ear; and vice versa for ear(b)...
This complex computing by the brain recreate holographic information VOLUME of the sound sources who become more than a point, a line or a mere surface,...
This is why the sounfiekld of speakers/room and from top headphone illustrate 3 characteristics of the SOUNDFIELD and not the traditional well known two :
-- imaging differentiation from the sound sources in relation with each other
-- Soundstaging integrating three dimensions in some GLOBAL stage , which can be fixed in less performant and artificial design or in a bad acoustic room but which are normally highly recording dependant for their dimensions size ...
---Holographical definition of EACH sound surces in his own dynamical VOLUME of space... The sound sources are no more a plane but a perceived 3-d relief an outline..