even star trek mentions ultrasonic , beyond to the dr. wants to render the crew disorientated unconscious but is going far beyond .
. it needs extremely high amplification to hear it ? what may appear say 85dB on spl meter or register easily on RTA doesn't or may mean i could perceive easily it needs to go way , way higher dB to notice it clearly and to a child they may start crying so practice extreme high/freq safely . to my cats it would be extremely an announce as the spl dB to them would or maybe extremely dB unsafe . just as someone places fish tank aquarium in the corner of room of their home theatre . the bass frequencies would be an extreme annoyance to the fish and be extremely harmful .
also mute all other frequency channels in active or dsp crossover . leave the ultra highs playing at say crossover region of -24dB L-R at 15KHz ? to where it would it be extending to beyond 20kHz and you should hear a "tisss , tisss , tisss" or may sound like distortion , (how i know this i can place crossover at 10KHz -24dB to filter off the resr of the sound and unless proper mix sound present ? otherwise it is rather boring to listen that high not much up there) anything but the sound of musical instrument or may try sine wave tone until it totally knackers your hearing with high frequency loss as well as tinnitus , enough to start banging your head against a wall when the hissing inner ear noise won't stop .
online hear test . i use this it shows a clear graph . remember do a test must be done with no background sound noise . better done at nighttime around 1am and in 1 quiet isolated room or make sure any fridge or ac system is switched off . see if you can hear the down to the lowest the hearing test goes -99dB and depends on the freq of the headphones ? once get near to 8KHz it slowly drops off , and needs to be increased just to notice 12KHz or 16KHz . even using the denon avc-x8500h headphone output provides enough signal output than the laptop . also be aware some devices can easily start distorting the sine wave signal near to 16KHz so find good source device or check it on oscilloscope that it is putting out pure clean wave form .
This free hearing test on line is an interactive test to produce equal loudness curves or equal loudness congtours.
newt.phys.unsw.edu.au