Hey Jeff! I got this article a plug since I thought it a worthwhile read.

http://urbansurvival.com/coping-from-the-cynics-notebook/

Best regards.

Perhaps ‘rule out’ wasn’t the best choice of words, but such things as traffic are pretty ubiquitous these days and you made no mention of it. Also traffic generates a very low frequency sound that travels very well and couples with architecture effectively. These low freq vibrations are sure to create higher freq tones that would be involved in the sound of the ambient space.

Then too, when we talk of the very low dB levels of the ambience of quiet spaces, perhaps the self noise and resonance of the mic/stand can contribute as well. I worked at a studio where we had a problem on one session when we’d rented a bunch of very good mics to record a small orchestra and when they were all on, only then could we hear the rumble of the trucks on the street. Still, it was there.

In a related scenario I was in Joshua Tree National Park on a quiet afternoon and I could hear a fly buzz 50′ away and a jet high overhead echoed for 5 minutes. Nothing is ever silent.

I’d love to hear some of these as you describe.

I’m not sure how you mean ‘rule out’ Dave. If it’s in regard to resonance, then intrusive sounds may or may not play a part, but it’s usually only intermittent (and so not the ambience of the space itself).

Resonance operates on continuity of sound frequency/energy (as with a constant wind that activated resonant frequencies of the bridge in the famous 1940 Tacoma Narrows Bridge collapse). http://www.youtube.com/watch?v=j-zczJXSxnw

Intrusive or intermittent sounds can trigger resonance, can even help you hear the resonance of a very quiet space better as spatial overtones will pop out if activated. But the ambience of the space is ambience – a continual backwash of resonant activity based in the air motion of the space and the architecture.

Some spaces have that constancy fed by other wide frequency bandwidths that can trigger resonance, like the sea or a constant rain or climate control. Other frequency-specific intrusions might be constant but not activate the space, such as electrical hums.

I had the opportunity twice to make recordings in the Cathedral of Cologne, Germany between 3-6AM. On both occasions I had the sexton turn off all power in the space – and so had the place entirely free of tourists, traffic and noise in the town square outside – it was as silent as the place could become. There were a few trains that arrived in the nearby station and as 6 AM approached more and more street noise. On one evening it rained part of the time. But one night it was very clear and very, very quiet.

Even in the ultra-quiet it could not have been anywhere else – I could hear it.

Thanks Randy, much appreciated. I agree with you that our brains probably are subconsciously in touch with these background sounds. A problem is that urban life is filled with too much chaos, so in self-defense we shut down the connection with the background. On the other hand modern architecture seeks to quell noise by acoustic damping. But by doing so it diminishes our sonic sense of space so that, in essence, we can’t hear where we are. I’d like to see architecture that was sonically smarter, but beyond film sound has the potential to return a sense of reality that’s not in the reality!