Free reeds as pressure-controlled valves
James P. Cottingham · The Journal of the Acoustical Society of America · 2012
The analysis of excitation mechanisms in pressure-controlled wind instruments by Neville Fletcher in a 1979 paper [Acustica 43, 63-72 (1979)] and later papers has been applied in understanding the operation of free reed instruments. This analysis enables calculation of impedance curves for reed generators and yields the well-known result that an inward striking reed coupled to a pipe operates at a frequency below the reed resonance and below but close to the frequency of an impedance maximum of the pipe, while an outward striking reed has operating frequency above both the reed resonance and the frequency of the pipe impedance maximum. This is useful, since free reeds can function as either inward striking or outward striking reeds, depending on details of the reed design and possible coupling with resonators. Fletcher’s analysis was first applied to free reeds in the harmonica by Johnston [Acoustics Australia, 16, 69-75 (1987)] and has subsequently been applied to free reeds and free reed instruments in a variety of ways, which are summarized in this paper. These include modeling the change in sounding frequency with blowing pressure as well as determining the sounding frequency of both inward and outward striking reed-resonator combinations.