The air just outside the hole radiates into free space. This has a real part (energy lost as sound) and an imaginary part (an added mass effect). For a small hole on a large tube, the radiation is omnidirectional at low frequencies. For a hole near the bell, radiation couples with the main bore’s output, causing complex interference patterns (the basis of bell modes ).
To aid overblowing (octave or twelfth), a small is placed near the mouthpiece at a pressure node of the desired harmonic. For a clarinet’s twelfth key, the hole is at approximately 1/3 of the tube length from the mouthpiece. Misplacement by millimeters renders the note unstable. The air just outside the hole radiates into free space
To design an instrument that is both in tune and tonally rich, a builder must master the relationship between the geometry of the air column and the placement of toneholes. 1. The Anatomy of the Air Column For a hole near the bell, radiation couples