OPEN AND CLOSED TUBE RESONATORS (CYLINDERS)
By convention a rigid cylinder that is open at both ends is referred to as an "open"
cylinder; whereas, a rigid cylinder that is open at one end and has a rigid surface at the
other end is referred to as a "closed" cylinder.
The first three resonances in an open cylindrical tube. The horizontal axis is pressure.
The first three resonances in a closed cylindrical tube. The horizontal axis is pressure.
Open
Open cylindrical tubes resonate at the approximate frequencies
where
n
is a positive integer (1, 2, 3...) representing the resonance node,
L
is the length
of the tube and
v
is the speed of sound
in air (which is approximately 343 meters per
second at 20 °C and at sea level).
A more accurate equation considering an end correction
is given below:

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