I couldn't really hear 18K over the harmonics. Really nasty lawl. I also was using my output card digital transfer to my receiver listening on my MDR-7506 headphones.
You would need to give the control of turning the sound on and off to someone else who you could not see. I think the 22khz just takes a little practice to hear. If you listen to is multiple times it becomes a little more noticeable but I still don't think I could hear it if this test was properly set-up.
I heard out to 20KHz, not bad for a 6.5" cone with no supertweet //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif