School for INNER SOUND
Acoustic Demonstration Kit
This acoustic demonstration kit is a
teaching aid for demonstrating a number of principles including those described
here to purchase.
By holding the square tube by the prong end and
effectively clamping the prong, then activating the 880 Hz fork and
placing it at the mouth of the half-wave end of the square tube, it is
possible to demonstrate that the tube itself is a half-wave pipe trimmed
to 880 Hz. The fork end of the square tube can also be activated and the
pipe detuned by closing the half-wave pipe mouth effectively
demonstrating that the unit is non-functional as a closed pipe.
By holding the square tube so that the fork is
free to vibrate and placing the activated 880 Hz fork at the open end of
the tube, the forked end of the tube will sympathize with the 880 Hz
fork. Duplicating the experiment with the 883 Hz fork it will be noted
that the fork portion of the tube will not sympathize even though the
half-wave portion will amplify the 883 Hz frequency.
By striking the tube and setting it into
resonance at 880 Hz, plus striking the 883 Hz fork and setting it into
vibration, then placing the vibrating 883 Hz fork at the mouth of the
tube the 3 Hz/sec hetrodyne can be heard.
By striking the 880 Hz fork, then placing the
handle end into mechanical contact with the tube as shown in the
photograph, a mechanical energy transfer point is accomplished setting
the tube into vibration.
The 883 Hz fork is provided with a hole in the
handle, through which a cord can be tied. The fork can be struck and
then swung in a circle demonstrating to students, outside the circle,
the Doppler effect.