Pressure wave reflections in a barred organ windchest
T. L. Finch, A. W. Nolle · The Journal of the Acoustical Society of America · 1985
The effects of windchest design on the pressure rise and hence on the starting transient of organ pipe speech have been investigated by Caddy and Pollard [Acustica 7, 277 (1957)] and by Lottermoser [Z. Angew. Phys. 20, 424 (1966)]. Their results were described by equivalent circuits with lumped constants. We show measurements of windchest pressure, pipe sound output, and wind velocity into the pipe foot as functions of time, using a 1.5-m-long note channel of a barred windchest with a hand-operated pallet valve. The results indicate that a long channel must be considered as an acoustic transmission line. For a rapid opening of the pallet, the pressure signal advancing along the channel consists of (a) a negative pulse due to the pallet displacement, followed by (b) a rising pressure step of height ps, the supply pressure. When the pulse is reflected from the rigid far end of the channel, a pressure pedestal of height approaching 2ps, and duration 2(length)/c is observed there. At other positions, the initial pressure rise is followed by a delayed further rise due to the returning reflection. [TLF is visiting Scholar, The University of Texas at Austin, 1984–1995.]