Ah ok. I hadn't written the TecTalk article with the intention of showing what you call '3D depth'. That's because it wasn't the point I was trying to convey. What I was trying to get across was that certain colorations typical to loudspeakers could bias our perception of where the sound stage appeared. (See article here for the full story).
Originally Posted by STHLS5
What I think you are commenting upon is how you interpret the well balanced, coloration-free left-right sound stage to give it some apparent depth. But whatever illusion of depth your brain conjures cannot be anything more than an enjoyable trick. That's because there is absolutely no real depth information collected by simple L-R microphones arranged across the sound stage. In fact, although the sound engineer may have sprinkled spot microphones from the front violin section to the tymps at the back of the orchestra 10 or more metres behind, he will have mixed the whole lot down to one 'flat' left + right mix, with all the performers overlaid on top of each other (in the Z , front to back) plane - unlike what you would have actually experienced at the concert hall. He may have taken an additional step of digitally time aligning the spot microphones relative to some fixed point - say relative to the violin section nearest the conductor - to 'bring forward' those performer's microphones deeper into the orchestra. There are subtle differences in the sound but you would have to be an expert to hear them so it's a technique rarely used - and impossible in the analogue era.
Alternatively you could be saying that the L-R sound stage seems correctly balanced (i.e. no obvious bulge towards you or dished away from you) but that the entire orchestra seems to have stepped towards your listening position (this is what I at first thought your picture indicated). The solution to that is simple. Turn down the volume! As QUAD's Peter Walker said - the volume control gives you the ability to zoom into the recording. In other words, to bring the performers nearer.
If we are able to construct a fantasy 3D sound image in our brain of illusory performers in space behind our loudspeakers the vividness and stability of this image is going to vary from listener to listener. It must to some extent depend upon preconceptions of how musicians arrange themselves in front of microphones, familiarity with the music and our ability to fantasise. I wonder if an Amazonian aborigine, completely isolated from western music were to listen to a pair of loudspeakers, would he hear '3D depth'? I doubt it.
Alan A. Shaw
Harbeth Audio UK