Influence of wall vibrations on the transient sound of flue organ pipes.
Malte Kob · The Journal of the Acoustical Society of America · 2010
The question of how the vibrations of a metal flue organ pipe contribute to the perceived sound has been investigated intensively in the last decades. Numerical, experimental, and theoretical works have shown that the influence can modify fundamental frequency, amplitude, and stability of the sound. However, these changes are small in the stationary sound of a pipe and vary with boundary conditions. Fewer investigations have concentrated on the transient sound of a pipe. As one result of the research done in a project within the Gteborg Organ Art center, it was shown that due to the casting process, baroque flue organ pipes often have considerably thinner upper ends than modern pipes. To prove the influence of the wall vibration on the perceived sound, recordings of a blown pipe with and without damping of the wall have been carried out. Furthermore, investigations of eigenmodes of the pipe under test using finite element calculations and pressure and velocity measurements with force excitation at the labium with subsequent modal analysis were made. The results confirm that some structural modes are excited when the pipe is blown and some components of the transient spectra change when the pipe is damped.