There are two primary types of reflections in a loudspeaker based stereo system: those that are created from the loudspeakers and those captured on the recording. To get proper imaging in your system you don't need both, as any good set of headphones would demonstrate, but since most of us have loudspeakers as our primary source we can have our cake and eat it too.
As we've been learning, in a live recording it is reflections of sound off of walls, floors and ceilings that give us the spacial information we need to localize, locate and place instruments and voices on our soundstage. When a recording engineer captures a a live performance he is both capturing the direct sound and the reflected sound on the microphones and hence we get a live sound.
But if the recording was, for example, all electronic and did not use any microphones, then we'd not have reflections to capture - the sound taken straight out of the electric guitar, synthesizer or what have you. It's easy to imagine then how a recording engineer would localize these instruments in the mixing console: left, right, center and everywhere in between depending on what they were trying to achieve. If the engineer wants a bit of depth, it can be achieved with the addition of some reverb or time delay - or he can simply reduce the volume to something less than the main sound and we will "assume" depth when we listen. This won't sound live but it will sound as good as the skill of the engineer (Norah Jones and Patricia Barber are good examples of great studio recordings).
There are other tricks that can be used as well, including phase cancellation and manipulation. Roger Waters Amused to Death and Madonna's Immaculate Collection are bothgood examples of this technique - which can be appreciated both on headphones as well as speakers.
Speakers add an entirely new problem into the equation however, that of additional reflections of the room. Depending on the type of loudspeaker used and the type of room treatment, you can get anywhere from extraordinary imaging (better than headphones) or dreadful imaging (worse than headphones) or what many people have, just ok imaging.
Tomorrow I am going to tell you about an idea I've had for some time that adds perhaps a new twist to all this. Just for fun.