At 03:24 PM 12/8/96 -0200, you wrote:
>I know that 40kHz is a standard for sonic range finders, but my question is:
>
>Has anyone tried a lower frequency ? How low can we get still keeping
quality ?
>
>TIA,
>
>Pedro Drummond
>


        Probably to the point of when you start to HEAR it!  :-)

                -Hamilton