open vs closed pipes

Consider a flute and a clarinet, two woodwind instruments that have a similar length and a similar diameter bore.  One is a closed pipe and one is an open pipe.

People seeing that a flute has a capped end, world probably think it's a closed pipe and that a clarinet with two open ends would act as an open pipe.  However, the exact opposite is true.  Here's why.

Even though a flute has one end capped, it uses what's known as an "air reed", in other words, the player blows across the hole near one end.  Air can freely move in and out of this end, so it's actually an open pipe.  

A clarinet has a single reed on one end, but since the player effectively seals the end with their mouth, air can only move in (and not out), so it's actually a closed pipe.

Because the air in a closed pipe instrument has to travel twice as far to produce a sound, the pitch is an octave lower than an open pipe instrument of similar size and bore.  That's why the lowest note on a clarinet, a concert D, is almost a full octave lower than a flute's lowest note, a concert C.

Most single and double reed woodwinds have register keys that are located near the reed end.  When this key is open, the closed pipe transforms to an open pipe, which produces a higher pitch.

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