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20kHz is still audio. Ultrasonic piezo transducers operate at 40kHz and have a flat wide frequency response.HerbertMunch said:where would you find a piezo that would resonate happily(and loudly) at 20kHZ?
Isn't classical music, or the threat of boot camp, an effective kid deterrent?
My first post on this forum and maybe my last.Take an astable 555 timer tuned for 18kHz and connect it to a piezo tweeter.
I don't really agree with the use of child repellers because they'll cause problems for people with good hearing and for dogs and cats. I also think that children should have the right to be on the street.
Also there's nothing stopping them getting ear plugs or a ghetto blaster that pumps out a loud enough bass line to cancel out the near ultrasonic tone.