A pen without refill is more or less a lambda/4 resonator (i.e. a
pipe closed at one end and opened at the other). If you blow in the pipe
and observe the spectrogram of the so produced sound, you'll measure
the standing wave's frequencies.
The pen I used (a bic) is 13.3 cm long.
The predicted frequencies are:
f0= 639 Hz; f1=1917 Hz, f3= 3195 Hz, f4= 4473 Hz
The measured frequencues are:
f0= 578 Hz; f1= 1758 Hz; f2= 3181 Hz.
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