Excitation mechanisms in woodwind and brass instruments

Abstract

A general analysis is given of the behaviour of musical instruments driven by a reed mechanism. Attention is concentrated on the reed mechanism itself and a clear distinction is drawn between the behaviour of reeds striking inwards (as in the clarinet, oboe and organ pipe) and reeds striking outwards (as in the trumpet and other brass instruments). Impedance curves are calculated for reed generators of each type and it is shown that sounding of the instrument requires that the acoustic admittance of the reed, as seen from inside the mouthpiece, should have a negative real part of larger magnitude than the real part of the pipe admittance. This implies that there is a minimum permissible blowing pressure for each reed configuration. A reed striking inwards must operate at a frequency below the reed resonance and below but close to the frequency of an impedance maximum for the pipe. A reed striking outwards must operate at a frequency above and close to the reed resonance and above and close to an impedance maximum for the pipe. Brief consideration is given to other matters, including non-linearities and their role in limiting oscillation amplitude and in generating harmonics.