Re: dispersion at Chichenitza

[Andy Piacsek <piacsek@TAHOMA.CWU.EDU>]

> At 10:47 AM 1/10/00 -0500, kyle forinash wrote:
> > there is a distinctive chirp in the echo; lower sounds
> > return faster creating an echo that rises in pitch.
> ...
> > Does anyone know exactly how this works?
>
> If you had reported a sound that *falls* in pitch there would be a
> beautiful explanation.  It would be a great demonstration of
> diffraction-grating physics.
>
> You don't need to travel to the Yucatan to observe acoustical
> diffraction.  Any building with exterior lattice-work on a sufficiently
> coarse scale will do nicely.  Actually most such buildings are nicer than
> pyramids, because they give you more options as to the angle of incidence.

Check out the article "Singing Stairs" in the January 16, 1999, issue
of Science News.  It summarizes a paper given by David Lubman at the
October, 1998, Acoustical Society of America meeting.  (I was at that
meeting, but unfortunately missed this talk).

Lubman notes that the *decreasing frequency* of the chirp is reminiscent
of the call of the quetzal bird; thus his theory that the Mayan's
constructed the stairs deliberately to mimic the bird's call.

This theory is somewhat in dispute.

Andy




                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


        Dr. Andrew A. Piacsek                 voice: 509-963-2723
        Assistant Professor
        Department of Physics                 fax:   509-963-2728
        Central Washington University
        Ellensburg, WA  98926                 piacsek@tahoma.cwu.edu