One day I was walking down the street in the French Quarter in New Orleans. Through the slightly-open doorway of a shop I heard the sound of a saxophone. Instantly I could tell that it was a live saxophone instead of a good recording through speakers. I had no line-of-sight to the saxophone, not even close as it turned out. All I could hear was the spectral balance of the reflections, and the dynamic contrast.
I have yet to hear a speaker that struck me as "natural sounding" which did not do a good job in the reverberant field. Bonus points for preserving dynamic contrast, but ime that’s a bit less critical.
Let me try to explain why getting the reverberant field right matters if the goal is "natural sound". First a bit of background: All new incoming sounds go into a short-term memory, and then all sounds are compared with those sounds in the short-term memory. If there is a match, then the sound is a "reflection", and it is largely IGNORED for localization purposes, but INCLUDED for its influence on loudness and timbre and ambience. If there is no match, then it is a NEW SOUND, and the ear/brain system figures out where it’s coming from (localization) and puts it into that short-term memory, so that its subsequent reflections can be correctly classified.
The way that the ear/brain system identifies a reflection is by looking at its SPECTAL CONTENT. If the spectral content of an incoming sound matches that of a sound in the short-term memory, then it’s a reflection. If not, then it’s a new sound. So far, so good.
But what happens when an incoming sound is in between - it kinda matches a sound in that short-term memory, but not very well? This can happen when a speaker’s off-axis response, which is responsible for most of the reflections, has significant glitches. What then? Well, in that case the brain literally has to work harder to correctly classify the incoming sound as a reflection. This extra CPU usage can actually be fatiguing, and can even cause a head-ache. You’ve heard the term "listening fatigue"? This can be one of its causes.
I’m not saying that a spectrally-correct reverberant field is the only thing that matters in the pursuit of natural sound, but imo it is one of the things that matters. One of the reasons unamplified instruments in a good recital or concert hall sound so delicious and utterly non-fatiguing is that the reverberant field is so well done.
When auditioning speakers, you may not always have time to find out if listening fatigue sets in. One way to quickly put a spotlight on the spectral balance of the reverberant field is to step outside of the room and listen through the open doorway, with no line-of-sight to the speakers. Does that saxophone still sound real?
Duke
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