Any sound above 20 000 Hz is called ultrasound. It is too high pitched for humans to hear, but other animals (such as dogs, cats, dolphins and bats) can hear ultrasound. Ultrasound waves are ...

(Credit: The Action Lab) Using a fairly beefy speaker to blast a 70 Hz tone at a big alcohol flame ... Using an air vortex cannon to focus the sound waves from the bass reflex port, it ‘wiggles ...

That is, for a signal with the frequency of 1 Hz, the proposed design can detect the minimum vibration of lunar geology is 10 −11 m. The location of the array is also carefully considered.