Tonehole Undercutting
Undercutting has been practised by makers of woodwind instruments for centuries. A skilled craftsman can shape the junction between a tonehole and the bore of an instrument to alter significantly the characteristics of a note played using that hole. Undercutting may be used to increase loudness, improve timbre and playability, make tuning adjustments and change the interval between notes in different playing registers. While undercutting is widely and effectively used, a full acoustical understanding is still developing. The effects of undercutting are not detectable in acoustical measurements made at low sound levels but rely instead on processes that are more apparent when an instrument is played loudly.
The current work in Edinburgh uses Particle Image Velocimetry on a simplified clarinet model to visualise the oscillating airflow around a tonehole over the timescale of a millisecond. The formation of jets and vortices has been observed at realistic playing levels and these phenomena seem to provide the key to understanding undercutting. Investigation into their effects on the acoustic field around the tonehole is underway.
