Quasi-Turbulent Damping at Wind Instrument Joints and Tone Holes

Abstract

The measured Q of air column resonance can fall quickly with playing level by a factor of three or more at fortissimo (SPL ≳ 143 dB inside first open tone hole) below the classical nonturbulent value associated with softer playing (SPL < 100 dB). The increased damping arises at all sharp-edged discontinuities in the bore, such as in mouthpiece receivers, valves, and tuning slides of brass instruments, and the sockets, tenons, and tone holes of woodwinds. Rounding these edges gradualizes the growth of the damping. Good instruments so treated become responsive and “flexible.” When an instrument is thoroughly warmed up, similar changes arise via the temperature dependence of the kinematic viscosity and thence of the Reynolds number. Rounding of even a single corner is noticed by many players. Rounding also produces a “darkening” effect on tone color, owing to reduction of nonlinear turbulent effects. Musicians recognize a tonal distinction between drawn and soldered tone holes on saxophones. Rounding the corners of the latter eliminates the distinction. Study of numerous instruments and modification of many confirm that rounding from long use is one way that age improves wind instruments, provided bore and tone hole dimensions are not deranged by wear. Care with rounding can eliminate many problems of “unvented” tone holes (such as hissing, stuffiness, and unclear tone) if they are also sized correctly to maintain uniformity of tone hole lattice cutoff frequency.