Hearing Damage over 20khz?

Even if the speakers can produce sound to 40Khz, there is so little music that hi up I doubt there is reason for concern. If 40Khz is causing hearing damage then the audible music would be unbearable.

The sound pressure in the UHF range is so miniscule it would not g=damage your hearing.
The total wattage used for normal music is 9grossly extimated)
like if using 100 watts total,
90 watts for the woofer, 9 watts for the midrange and 1 watt for the tweeter, so once you get up to supertweeter ot would be like 0.1 watt...
Of course that could be changed and some crazy device could be putting out a SPL that will make dogs a block away go deaf.. How would you even know without test equipment?

Okay, shooting from the hip... I've never heard of anyone having tinnitus at 20 hz,or even 250 hz, It'd be like a bumble bee living inside of your head. But this is where most of the wattage in our amps is used.
I think we all agree that we WANT the extended frequency in our audio systems because there's information above 20k that we don't hear, but there are subharmonics generated below these supersonic frequencies that translate into harmonic information and/or spatial cues in the range that we DO hear.
Rupert Neve, recording console designer extraordinaire has been designing audio recording equipment that is intended to reproduce up to 100k (100,000 kilohertz) and higher since the 1970's.
High frequency sound waves like this are pretty easily attenuated by walls and carpeting so unless the kids are right in the room with you it's pretty hard to imagine them
being harmed by it. I do however wonder about my dog's hearing when she sits beside me during listening sessions...

but there are subharmonics generated below these supersonic frequencies that translate into harmonic information and/or spatial cues in the range that we DO hear.

Subharmonics in a bell is called music.

Subharmonics from an audio system is simply unwanted added distortion!

If you add a device that is only supposed to make sounds above 20KHz (and nothing else) and then you hear a difference then you must necessarily be hearing distortion from said device.

If there is audible sound between 20 and 20 KHz and it is on the recording then you will hear it - irrespective of what source (instrument) made these sounds and irrespective of whether some of these audible sounds are subharmonics of higher frequency fundamentals of certain instruments (possibly percussion?).

The whole thing about sound reproduction above 20KHz is misguided at best - at worst it is deceiving.

The only valid argument for frequencies beyond hearing capabilities is that better performance beyond human hearing capability might mean the system performs more accurately and linearly within the bandwidth of human hearing. (although this may be doubtful as resonances outside the audible bandwidth may equally be a source of distortion)

Thought all responders may be interested in these related articles:

http://jn.physiology.org/content/83/6/3548.full

http://www.ocf.berkeley.edu/~ashon/audio/Ultrasonics.htm