Originally Posted by Zodduska
Actually, somebody correct me if I'm mistaken, but you might be hearing harmonics that exist in a lower frequency when you try the test at higher volumes.. I'm pretty sure these kind of tests rely heavily on proper calibration.
Well, maybe. If you increase the frequency of the tone, and perceive the tone as doing the same thing, I'd say it's fairly unlikely that this is the case. A harmonic is going to be higher or lower in frequency than the actual signal, so you'll probably notice it. You are correct, though; in order for any test to be conclusive, proper calibration is essential.
Your hearing doesn't have a hard set maximum limit. You might be able to hear 16 kHz loud and clear, then notice it gets quieter and quieter as you increase the frequency, until you reach a point where you can't hear it anymore. If you can only hear 20 kHz after cranking the volume, your hearing probably starts to drop off at some point before that.
Also, remember the equipment you're using. If your speakers or headphones can't reproduce 22 kHz at the same volume as 16 kHz, your results will be skewed. Not to mention that the vast majority of headphones and speakers aren't going to have a perfectly flat frequency response, anyway. That's where the calibration comes in.
Regardless of all of this, it's still a fun and interesting test. The results need to be taken with a grain of salt, however.