Nonlinear effects contributing to hand-stopping tones in a horn

Area of Science:

• Acoustics
• Musical Instrument Physics
• French Horn Performance

Background:

• Hand stopping is a French horn technique producing a distinct "penetrating" and "metallic" timbre.
• Previous research focused on impedance changes, neglecting the physical basis of the stopped-horn tone quality.

Purpose of the Study:

• To investigate the dominant physical cause of the metallic tone quality in hand-stopped French horn playing.
• To analyze the relationship between sound characteristics and physical phenomena during hand stopping.

Main Methods:

• Numerical calculations of the stopped-horn model's transmission function.
• Measurements of sound pressure and wall vibration during hand stopping.
• Excitation and immobilization experiments to assess sound radiation and wall vibration correlation.

Main Results:

• The metallic tone is associated with higher harmonics (>10 kHz) from a rapidly corrugating waveform.
• Wall vibration on the bell was initially suspected but later experiments denied its correlation with higher harmonic generation.
• Mouthpiece pressure measurements suggest nonlinear sound propagation along the bore is responsible for wave corrugations.

Conclusions:

• Nonlinear sound propagation within the French horn bore is the likely cause of the metallic timbre produced by hand stopping.
• The generation of high-frequency harmonics is a key characteristic of the stopped-horn sound.
• Further research may explore the precise mechanisms of nonlinear acoustics in brass instruments.