Space...the Final Frontier SIDEBAR 1
Is soundstage depth a psychoacoustic illusion brought on by strong reflections of the speakers' sounds from nearby walls? While there's no doubt that discrete sidewall reflections can lead to beyond-the-speaker lateral imaging, and that planar speakers produce very strong reflections due to their undamped full-range backwaves---which do contribute an added sense of spaciousness---conventional monopole speakers tend to be quite directional in their upper midranges and above.
This is true even with small speakers. Fig.1, for example, shows how the response of a minimonitor widely regarded as throwing good soundstage depth, the Rogers LS3/5A, changes as the microphone moves from the tweeter axis at the front to behind the speaker (footnote 1). The LS3/5A's narrow baffle does contribute to wider-than-usual dispersion in the mid-treble, the axial response holding up over a wide