Register holes suppress unwanted modes by exploiting pressure nodes and maxima

Evidence

To suppress the first mode in this way without affecting the second, this hole should be drilled in a position where the undesired mode has a pressure maximum. When all the tone holes are covered, this would be exactly halfway down the resonator—a point at which the first mode has a pressure maximum and is therefore reduced, but the second mode has a pressure node and is therefore unaffected (see Figure 4.18). Register holes can be placed at other positions to enable overblowing to different modes. In practice, register holes may be set in compromise positions because they have to support all the notes available in that register, for which the effective pipe length is altered by uncovering tone holes. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1193

Categorization

• DEFINE: Explains the acoustic principle behind register holes in woodwind instruments—placement at pressure maxima/node positions determines which modes are suppressed.