A 25-cm-long wire with a linear density of 25 passes across the open end of an 83-cm-long open-closed tube of air.

A 25-cm-long wire with a linear density of 25 passes across the open end of an 83-cm-long open-closed tube of air. If the wire, which is fixed at both ends, vibrates at its fundamental frequency, the sound wave it generates excites the second vibrational mode of the tube of air.