Tim, here is the earlier post I mentioned in which I define what I mean by the term "natural". There is no reference to "diffuse" sound. There is little mention of what it is NOT. Some might find my post unclear, or not specific enough. I can't help them. To me, it is a pretty simply concept that does not need a lot of explanation. Here is that post again:
Tim, I do not think I answered your question very well, certainly not completely. Referencing live music and comparing it to reproduced music is certainly my process, but having thought about it a bit more now, I can be more specific.
Natural Sound:
I agree with David that everyone knows natural sound when he hears it. However, as he also states, there is more to it. I think about his comment that "music is not bits and pieces". We collectively as audiophiles have been taught to think of bits and pieces - the breaking down of music into sound into sonic attributes. We have a glossary of audiophile sonic terms. We have books that keep being referenced. We have reviews that go into much detail about aspects of the sound. There is so much "flowery prose" as Fransisco, Kedar and others mention. I know I am just as prone to this as others.
Years ago, after I began to attend Friday afternoon concerts at the BSO with my father, and on occasion Madfloyd and Al M., I remember always returning to one strong impression of the sonic experience of such an event: The sound is so clear. I always return to that one impression. It overrides all other impressions. Some might find it vague. Having talked to David over this last year, simplifying my system, understanding natural sound, I realize that David is right: music is not bits and pieces.
When I say the sound at the BSO is so clear, what I am also saying by omission, is that I don't think of the sound in that great hall in terms of sonic attributes, the audiophile glossary of terms, or broken down into bits and pieces. I think of the whole, the holistic experience, the gestalt. This is what natural sound means to me.
I never think about frequency response, tonal balance, "tight" bass, poles of articulation, grain, etch, fatigue, brightness, slam. When sitting in my seventh row center seat, I take in the sound, the music, and its overwhelming clarity. Clarity because this is energy at its source in a well designed real space, not some semblance of that energy after manipulation through the recording and reproduction chains.
David also talks about listening to a system or a component and hearing if anything draws attention to itself. As soon as his mind goes to some aspect of the sound rather than the gestalt of the music, he gets concerned. This is an indication that there may be something now quite natural. If the listener pay attention to a frequency range, or some specific detail, and keeps returning to that, it is not natural sound.
When I told David that I was now hearing "more" of what is on the recording and is sounded more convincing, he told me that was "natural resolution". A. J. van den Hul writes about getting more information from the grooves from his latest designs. Natural sound is the embodiment of energy being set free in the listening room, and of extracting the information from the recording. There are degrees of this. A modest system can do it as long as this energy and information is not corrupted. This goes back to the idea of doing no harm to the music. It it just that better components, a better system, better set up and a better room, all contribute to a better, more complete and more natural listening experience.
I knew I was getting closer and closer to natural sound during my period of experimentation when I thought less and less about sonic attributes, and more about the music. When Al and I sit in my room and he requests some violin concerto or choral piece, and we just sit and listen and talk about how brilliant Bach or Holst was, that is an indication of natural sound. When Al could no longer hear a high frequency accent from my vdh Grand Cru or Magico tweeter, that was an indication of a more natural sound. When we discuss Art Blakey's drum solo and the rhythm and impact of his sticks on the skin or metal rims rather than the tight bass or sparkly cymbals, that is natural sound. When we listen to Holst's chamber opera and marvel at how Death moves forward on the stage, and we are moved by Savitri's love for Satyavan and her fear of the forest creatures, that is natural sound.
This was made super clear to me the other night when I visited Al to hear his isolation transformers. With the transformers in place, I heard "tight" bass, a focused organ and voices, a slightly harsh triangle, a sharp trumpet, a restricted soundstage, and focused images. Without the transformers, I heard an expansion of energy in the room, a more convincing presentation of musicians on a stage, and the music, not the sonic attributes. This is how I knew that his system sounded more natural without the transformers.
The overwhelming impression for me at the BSO is one of clarity and the sheer energy from the instruments. When I can hear some of that in my listening room with much of the information intact and uncorrupted, I know the system is getting out of the way, my mind is not focusing on specific sonic attributes and the glossary of audiophile terms is the last thing I am thinking about. That is when I know the sound is approaching a sound that I perceive as natural.