An echo isn't a matter of wavelengths, it's a matter of timing of return of the sound. Any return of reflected sound that comes back after the initial sound has finished is an echo. Any sound of the right volume and in the right place WILL create an echo. However, ducks are rarely quacking in places that are conducive to the production of echoes, and tend to go on and on anyway, so it is unlikely that you will hear a duck echo. This is not to say that the quack doesn't echo.
Apr 25 2007, 9:56 AM