PASCO WA-9857 String Vibrator - Manual (Page 12)

String Vibrator Closed Tube Analogy
12 ®
4. Adjust the hanging mass (or the driving frequency) so that there is a node at the blade and an
anti-node at the knot connecting the thread and the elastic cord.
Demonstration
This demonstration is analogous to sound produced by a pipe with one open end and one closed
end. Notice that the segment with the anti-node on the end is a quarter wavelength, where the
other segments are half wavelengths.
A dark background placed behind the wave can hide how this is done; the white elastic cord
shows up very well, but the black thread disappears when the String Vibrator is running.