Re: Resonance Demo

[Leigh Palmer <palmer@SFU.CA>]

> The box is divided into 3 sections.  Mounted in the center section are 2 - 8"
> woofers aimed at opposite ends of the box.  The speakers are wired in
> parallel,
> thus in phase.  There are three holes cut in the top of the box, one above the
> speaker section, and one at each end of the box.  This produces
> low-high-low or
> high-low-high pressure above the holes and causes a 24" x 3" piece of
> untempered glass to vibrate (f~34 Hz).  Drive it hard enough and it will
> break.

Sounds like it's driving the equivalent of a xylophone mode.
May I suggest that, for maximum efficiency, you rest the
glass plate on rubber bridges placed at points 0.2242 of the
length from each end of the glass (5 3/8 inches if you
really still use those units)? They are the nodal points for
the fundamental mode of oscillation. Four sharpened upturned
rubber stoppers should work nicely. Accurate placement of
these "bridges" will help this demonstration work at the
lowest possible sound pressure level.

For more information on this, and possible extensions of the
use of the apparatus which will suggest themselves, I
recommend Harry F. Olson's "Music, Physics, and Engineering".
Information on this is to be found on pp. 76-77.

Leigh