Answer 1

For a demonstration of human hearing frequency range, get a bunch of people from various ages, make them stand in a matrix from youngest to oldest, blindfold them so they wouldn't see what other people are doing and start giving them simple commands ("turn right", "raise arms") starting from 100hz and increment that range by 1000hz (or whatever you feel is best) until noone makes a move anymore. Have a camera to record it from the top.

Answer 2

With the new Nexus 6 and 9 coming out and since they can listen to "OK Google" commands even when the phone screen is not on, broadcast a command above human hearing levels and see the results.

20kHz: "OK Google. Where is the nearest doughnut shop?"

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