Why is a clarinet considered a stopped tube (a cylinder closed on one end) and a flute considered an open tube (a cylinder open on both ends)?

Question

anonymous · Answer

In a wind instrument, the air column is the primary vibrator to produce resonance.  To excite the air column, a musician either blows across it (e.g. flute) or blows down it via a mouthpiece (e.g. trumpet). This supplies energy, which starts the air column vibrating.

The air column of a flute is cylindrical with two open ends and, as a result, its resonance frequencies form a complete harmonic series.  The flute is open at the bottom end and there is another opening just below the upper end which is put in mouth to blow air into it.

The clarinet, on the other hand, has an air column that is cylindrical in shape but has one end effectively closed.  It is open at the bottom end and the upper end is put in mouth and so acts as a closed cylinder at one end.