The clarinet is unique among the woodwinds in that it has a cylindrical tube, whereas the tubing of the oboe, bassoon and saxophone is conical.

The cylindrical form, which is closed at one end and open at the other, lends the instrument the acoustic properties of a stopped organ pipe: it sounds an octave below a conical instrument of the same length and when sound is produced only the odd harmonics speak which means the first overblown harmonic is the twelfth (not the octave).

To play, the reed is placed on the lower lip, which is pressed against the lower teeth while the upper teeth grip the mouthpiece on the closed side. When blowing the clarinet, the reed is controlled and set in motion by means of lip pressure, air pressure and the points of contact between the reed and the lower lip. The vibrating reed sends little puffs of air into the air column inside the instrument, thus causing the air column to vibrate.

When attacking strongly in the low register the reed hits the mouthpiece; in piano it swings freely and does not touch the tip of the mouthpiece – beside producing a soft and clear sound this also makes it possible to play a pianissimo that can fade to complete silence.

The notes of the clarinet’s compass are produced either by opening or closing the appropriate tone hole or key with one finger or by a fingering combination.

The clarinet’s fingering is rather more complicated than that of the other woodwinds. This is due to the instrument’s unusually long fundamental compass; because it overblows to a twelfth (3rd harmonic = octave + a fifth) its fundamental compass consists of nineteen half tones. To bridge the gap between the highest notes of its fundamental register (on the Bb clarinet Eb4–Ab4) and the first overblown note, difficult fingering combinations are used.

If the clarinetist attacks normally, the written compass from E3–Bb4 is produced with the help of the keys.

On the clarinet, overblowing is achieved with a speaker key. The first overblown note is B4, a twelfth above E3. The range B4–C6 is produced by first-degree overblowing (in theory this is possible to F6). From C#6 second-degree overblowing is used (from E6 in the French system). In addition, special fingerings with keys are used to correct intonation.

Sound production on the Bb clarinet:

• D3–Ab4: normal attack (from the fundamental)
• A4–Bb5: first-degree overblowing (to the 3rd harmonic)
• from B5: second-degree overblowing (to the 5th harmonic), special fingerings

Many notes, especially those in the upper register, can be played with one of several fingerings. It is up to the clarinetist to choose the fingering best suited to the passage being played.