Some people can hear an extremely high-pitched sound generated by
television CRTs and television cameras. I have long wondered what
frequency this sound is. So, I am looking around for test equipment to
help me measure it. I plan to use an audio generator (which I can buy
for about $200), but I need to find a set of headphones that can
produce sound at these high frequencies. The low end frequency should
be about 12 kHz, and I would like to be able to go at least to 50 kHz.
I am guessing the sound is somewhere around 40 kHz.

Incidentally, I just got my hearing checked by my ENT (Ear, Nose,
Throat doctor). I measured in the 5-to-10 dB range on both the eardrum
and nerve conduction tests across the entire measured frequency range
(up to 8 kHz for eardrum, 12 kHz for nerve conduction). My doctor said
that they want to see values less than 20 dB, so I am well-within the
safe zone, as far as they are concerned. However, one reason that she
scheduled this test for me is that I complained that I am going deaf in
one of my ears. I have almost completely lost my sensitivity to the
ultra-high pitched sound in that ear. I can hear that sound 100 times
better from my other ear.

People don't realize what a difference it makes to a person's
perception when the range of hearing differs. I can walk into a room
with other people, and they think they are in an empty room. If there
is an operating television in the room, I will be aware of almost
physical contact. Other people can hold a conversation in a normal
voice, but I have to listen over a sound similar to a dentist's drill
or a jet engine. After several minutes of that, I often feel dazed. No
one else even notices anything, except maybe that I am acting a little
more odd than normal.