duldul123:
Hey Thanks for that... im using ultrasound to transfer a code to a phone... So i actually do want to make sue humans cant here it.... 20k is used because the phone microphone has a die out beyond 22k... i been recording the ultrasound and using a fourier transform library on the phone that give be a power output. So i can measure if the sound is being generated. I will try using the transducer you'v mentioned.Coming back to the amplifier question, how do i connect it to an amplifier. For the time being i am using an 8w 8 ohm buzzer that i got from a set of altec lansing speakers..
You can't make it 20kHz and expect humans to hear it. We can't hear sounds generated at that frequency, it's at the very outer edge of what even a baby can hear, and even then it would be EXTREMELY soft. Adults max out more in the 15kHz range. Here's a website for you to test the maximum frequency you can hear.
Therefore, it doesn't matter how big the amplifier is, you're not going to hear a 20kHz signal.
Tim