About 900 feet.
There is no true answer. Theory was that people can't hear beyond 20k, but with people noticing differences in tone with SACD that can go up to 50 or even 100k something is missing in our measurement system. I think there is some sort of body awareness of ultra high frequencies that we cannot guage yet. The short answer is around 22k. not allowing for my sound awareness theory.
Though there are systems that can reproduce high frequency content and though we may be able to hear it, if we're trying to reproduce a realistic musical experience, we might keep in mind that air absorption alone in a hall will cause a 10-12dB attenuation at 15kHz at a distance of 100ft (not to mention the effect of the audience and their clothing). Recordings made with microphones placed in the near field and/or too high above the audience position that are then reproduced on such systems will almost always be too bright for my taste. (YMMV)
The perceived differences correlated with system response characteristics occuring beyond the nominal range of human hearing are almost certainly caused (if real) by their effect on the in-band spectrum. This would presumably entail the effects of ultrasonics on either the electronics reproducing the music in their presence, or the absence of the effects of the filters that are usually employed to remove them. But the reported phenomena almost certainly have nothing to do with some sort of supposed extra-sensory perception beyond the human ear's physical limits. IMHO.
When I was still a teenager and before, and maybe up into my early 20s I could hear ULTRASONICS. Yes, it is true. The TV's 16.58khz was easy (is that the right freq?). When the Museum of Natural History was robbed by "Murph The Surf" and he took the Star of India Ruby, they decided to install ultrasonic detectors. Apparently they ran all the time, they just turned off the *indicators* during the day. I went in there and couldn't stand to be in my favorite room in the Museum! Very uncomfortable.
Many tweeters were unlistenable totally because of the out of band, and top of band crap - I remember a local fellow who had speakers with a pair of Janzen tweeter panels and a room of people who thought it sounded just fine. I heard this awful crackly stuff on top of the music. I said "don't you hear that" and received blank stares...
Can't hear up there anymore :- (
But it makes it plausible to be in the vicinity of things like power saws, other machines and the like... couldn't stand it as a kid.
So, different people hear very different things...
It is possible that such "intermodulation products" in the audible band may affect the perception of sound. As of right now, it is only "accepted" that the presence of ultrasonic content in combination with low frequency (i.e. conventional audio band) content induces activation of alpha EEG rhythms in the occipital region, which rhythms are not present when playing low frequency content alone. (See, e.g., Oohashi et al, Non-Audible High-Frequency Sounds Affect Brain Activity: Hypersonic Effect, J. Neurophysiology Vol. 83, No.6). The mechanism for this is still being studied. However, some of the research being done now with the profoundly deaf is pointing to the conclusion that these in-band effects to which you are referring are not the cause (or the sole cause) of perception of such ultrasonic information.
So Rzado your last point could indicate that the inner ear might not be the only region on the human body which can be stimulated by high-frequency sound waves. This of course is already known to be the case for low-frequency waves. This if true could be something that varies widely with individual physiology, but the "profoundly deaf" description also sends up a red flag - there could be exta-ordinary compensation going on in the brain here to extact any potential stimulus from the environment which hearing people may not perceive due to the way the brain develops. Who can really know? But I still doubt that any of these possibilities actually has something important to do with questions of concern to most audiophiles - for that, I'm betting on my first post.
Actually, Zaikesman, I think you are conveniently misreading my post. First, the research I am disussing still points to the the ear mechanism (not "extra-ordinary compensation" as you claim) as being what perceives the ultrasonic frequency content. Second, your conclusion that "you doubt that any of these possibilities actually has something to do with questions of concern to most audiophiles" simply doesn't follow - in fact, it stands contrary to reason. It is not disputed that ultrasonic frequency content affects perception of sound - and, indeed, the ultrasonic content almost universally resulted in both more realistic, and subjectively preferred, sound. No one has been able to replicate this phenomenom with in-band frequency content. Thus, I think most audiophiles would absolutely be concerned with this reproduction of high frequency content.