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. 

Doppler Effect

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.