Acoustic behavior of chimney pipes
S. J. J. M. F. Kokkelmans, Marc-Pierre Verge, Avraham Hirschberg, A. P. J. Wijnands, R. L. M. Schoffelen · The Journal of the Acoustical Society of America · 1999
The objective of this work is to study the acoustic behavior of chimney organ pipes. The working hypothesis is that its role is to reinforce the fifth harmonic of the tone of a stopped pipe. According to Helmholtz, the chimney should have the length of an open pipe resonating at the frequency of the fifth harmonic. This design appears to be the least favorable one, except if the chimney is placed half inside and half outside the main pipe, and should therefore be avoided. The ratio of the modulus of the admittance of the different harmonics appears to describe, for the chimney pipe used in this study, the dependency of the ratio of the measured amplitude of the fifth, third, and first harmonic with the geometry of the chimney. The admittance curve can therefore be used to determine the effects of the geometry of the chimney on the timbre of the organ pipe. This result is used in order to determine the optimal diameter of the chimney as a function of its length.