The illusion of soundstage.

Altering the relationship in time of one frequency to another is quite easy to detect with the right tools. It's quite easy for you to measure using something like Room EQ Wizard as well. However almost all of this is caused by the speakers themselves. I've seen no evidence that the most basic and common of amplifiers introduce any phase shift at all. 

In any event, if this were true, then tools like Dirac Live or RePhase+miniDSP would be able to compensate for it completely. 

Best,


Erik 

A number of the responses got it correct...  It is a function of wave theory and the fact that what you hear is not a single wave.  It is the complex interactions of 2 sets of waves arriving at different times to each of your 2 ears.  Right and left speakers waves (actually oversimplified since most speakers have multiple drivers) interact with each other.  

The behavior of waves; interference patterns, comb filtering, nodes/anti-nodes, etc. impact the sound level and timing that each of your ears perceives.  Your brain then "steers" your perception of where the sound appears to have originated.  Functionally, light and sound waves behave similarly so if you want a visual, google light interference pictures.  The most extreme example of this effect is with noise cancellation headphones which creates a perfectly out of phase sound to the actual noise and the two waves completely cancel each other out.

The degree of sensitivity to timing delays between your ears becomes evident when you are swimming under water.  Because of the density of water being greater, the speed of sound increases and therefore the delay between your two ears becomes shorter.  As a result, human beings more or less can not decipher directional clues from sound underwater...  Gives us a few million years under water to evolve and we would likely "recalibrate" and be able to decipher those clues.  Dolphins, wales, and all other sea mammals have similar ears to humans and other land mammals but they all relay on echo location to "see" more than eyes.

In summary, if a louder sound wave originates from the left speaker and a softer identical, but out of phase, wave originates from the right speaker, our brain will interpret these waves as if the sound was originating from outside left of the left speaker.  As one respondent correctly states, Q sound accurately maps these interactions and sound engineers can actually steer the sound not only to either side of the speakers, but even around your head.  For this effect to be completely realized, you must be sitting in the "sweet spot", equal distance from the two speaker... and of course above water level...

No offense but that explanation Re two waves interfering etc. Is either incorrect or incomplete since you can under good circumstances get a reasonably good soundstage with a mono recording and a single speaker, for which there is obviously only a single wave. I'm not saying there isn't interference between the left and right channels in stereo I just don't believe that explains how we get to the point of a great soundstage. I suspect there are many reasons for great soundstage, including but not limited to, noise and distortion produced by jitter or mechanical vibration, magnetic field interference, scattered laser light in digital, seismic vibration, interconnects and fuses in the wrong direction.