You're gonna have to link me to some study that says 12 kHz is the average, because that seems really unlikely.

I'm searching for it during the moment.

28, male: 13Hz~22kHz.

I can't find the exact passage but it was to be found in one of the document the teachers had prepared for us and based on serious studies. The thing is that I followed many courses and I can't remember in which I have read that.
 
Anyhow I typed high frequency audiometry on Google Scholar and pretty much all the studies agrees that the big thresholds shift happens at 12 kHz. At this frequency thresholds start to lower by increments of 20 dB SPL per every raise of 1 kHz. And that's for 10-19 years old... the thresholds are even lower for the 20 to 29 year older, but not inaudibly lower, I give you that!
 
It means that you can be hearing from 250 to 12 kHz hearing at a constant low (/ minimal, in real testing conditions) instensity in dB SPL, but to hear 13 kHz you need to raise your volume by 20 dB SPL (and some studies say 30 or even 40, and that's quite loud for a pure tone noise!) and so on, 40 dB SPL for 14 kHz, 50 dB for 15 kHz, and 100 jack hammering dB SPL for the 20 kHz many of you said you heard (by maxing out your amp? I hope not. Personally, I have done the test by calibrating my volume on normal listening levels for the 8 kHz frequency).
 
Looking at the graphs of those studies, for the people older than fifty, it shows that you can't hear the 12 kHz at all because your hearing thresholds, on average, should be at -100 dB SPL. And like I said, -90 dB SPL is the most severe case considered; it is called deafness or anacusis, when applied to the useful frequency band.
 
Here you go, http://informahealthcare.com/doi/pdf/10.3109/01050398509045936 first graph, -25 dB SPL threshold at 12 kHz for the 20 to 24 years old normal ears.
 
-35 dB SPL for the detection of 12 kHz with 20-29 yrs old male and female http://informahealthcare.com/doi/pdf/10.3109/01050397909076304
 
-40 dB SPL threshold for that very same freq. http://occmed.oxfordjournals.org/content/51/4/245.full.pdf 18-38 average though (that's for older people though and less reliable for describing the hearing of after-18 yrs old people)
 
only -13.3 dB SPL at 12 kHz for 20-29 people http://scitation.aip.org/getpdf/servlet/GetPDFServlet?filetype=pdf&id=JASMAN00005200002B000585000001&idtype=cvips&doi=10.1121/1.1913149&prog=normal
 
-36.6 for the 10 to 19 years old! (but the results are very similar to with the 20 to 29) http://scitation.aip.org/getpdf/servlet/GetPDFServlet?filetype=pdf&id=JASMAN000086000004001384000001&idtype=cvips&doi=10.1121/1.398698&prog=normal
 
Anyway you get the idea (I'm just giving out the studies in the order I find them on Google), at 12 audiological kHz (not the easy to hear thing on mosquitos or YouTube) you need to multiply by four or by eight the effective pressure to hear it minimally so you can press on that little red button when you're sat in an audiological cabin and that an audiogram is being made out of those button presses. And those sounds are a lot harder to notice in controlled conditions (when the volume is kept minimal and not maximal like some here might have done) and without the static noise you hear when you press the play bubble for example on this website http://www.noiseaddicts.com/2011/06/mosquito-ringtones/ (it's easy to focus and expect a sound to come after you press play, now turn your back and ask someone else to press play in your stead... it won't be as easy anymore I say)
 
 
Oh and yes, saying no one can hear past 12 kHz is dramatization, and I hope that's not what I said. What I say now is that: most "normal" (that hasn't been exposed to dangerously noisy work environment) people can hear from 250 to 12 000 Hz on minimal, low and regular listening levels (depending on how good you are in that very average). Past 12 000 Hz, your threshold is lowered by at least 20 dB SPL (but up to 40 if you are in the lesser tiers), so you need to add that volume to compensate and hear 13 kHz again... and so on for the other freqs.
 
Only newborn infants can hear 20 kHz on normal listening levels, you guys must have pumped a lot a volume to be able to discern that ultrasound thing out of the silence, it's called an ultrasound because you shouldn't be able to hear it at all. BUT it is also completely possible that you guys have a superior auditive sense, some of you. But not newborn superior still...
 
Also keep in mind you can always go and take an audiological test, ask the audiologist to go beyond 12 kHz and all the way up to 20 kHz but you might be deceived by your audition if you thought your results on mosquitosringtones.com were good.

double post sorry, can I delete it?

I knew all of that already (though not specific numbers). That's the Loudness Curve in action. That does not mean we can't hear that high. You implied we couldn't hear that high at all. I quote (bold added for emphasis):
 

Earlier in my longer post I said the average highest hearable frequency for an adult (starting from 18 years old) was 12 kHz.

Click to expand...

 
Do you have anything that supports that? Your above post doesn't.

I couldn't hear anything past 16khz.

Male and 27. That's probably one reason I flunk alot of the mp3 tests around here.

absolutely not... only up to 17,000 

 
Quote:

head injury said:

I knew all of that already (though not specific numbers). That's the Loudness Curve in action. That does not mean we can't hear that high. You implied we couldn't hear that high at all. I quote (bold added for emphasis):
 
 
Do you have anything that supports that? Your above post doesn't.

Click to expand...

Yeah.. yes. No; nope.
 
Good job on defeating me. If we were in Diablo II I would hope you'd keep my ear.

Quote:

devouringone3 said:

Good job on defeating me. If we were in Diablo II I would hope you'd keep my ear.

Click to expand...

Eww, why? It can't even hear past 12 kHz 

Male, 16, 20khz (had to struggle to past 18k though)

I have done tests on my own and I can hear pretty much all the way up to 20k but certainly not past. (I'm 19)
 
Just to reply to others: yes it is possible to hear past 20k, but frequencies past 16k don't actually matter for music so if you can only hear up to 16k you aren't deaf. That's fairly common. 

An equal loudness contour plot for everyone's viewing pleasure:
 

8khz yes
10khz yes
12khz yes
15khz yes
14khz yes
16khz yes
17khz yes
17.4khz yes
18khz yes
19khz no
20khz no
nothing over 19khz for me.
 
Male, 28. using iBasso D3 > Fischer FA003

Male 33 - 20-18K...by 19K its gone...funny thing I noticed is that I also have some loss in the left ear between 14 and 15k.  Didn't expect that....
 
Edit: I wonder if gear has anything to do with this test.....then again, I shouldn't go there....