Register holes force overblowing by stripping the fundamental of its harmonic support

Evidence

A small hole called a register hole, speaker hole, or octave hole is employed in some woodwinds; two are used in a saxophone. The hole is placed near an antinode of the lowest playing mode, which is to be rendered unplayable. The hole dampens the mode (the hole is a leak and a source of friction) but more importantly raises its frequency. The frequency shift strips the fundamental of harmonic support, since the harmonics of the raised frequency are no longer resonances. The reed goes looking for something better—namely, the next available higher mode, which does have support of higher harmonics. This is an octave higher for an oboe, or a twelfth higher in the case of a clarinet or other closed-open pipes. — Eric J. Heller, Why You Hear What You Hear- An…, 1590

Categorization

• DEFINE: Clear explanation of what a register/speaker/octave hole actually does mechanically, beyond the common hand-wave that it ‘helps players overblow.’