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  Figure 11. Top left: sketch of a chimney organ pipe. a–c: Measured spectra (black) and calculated input admittance (red) of the experi- mental chimney pipes. a: Reference chimney pipe design. Numbers on the blue background are the amplitudes of the first seven har-
bers on the yellow background show the same changes in the levels of the other harmonics. As can be seen, the op- timized resonators can enhance the targeted harmonics by more than 15dB while keeping the fundamental frequency constant. This amplification can be considered substantial if one takes into account that the experimental pipes only dif- fered in the geometry of their resonators.
The intention of the authors of this paper was to demon- strate that the research on organ pipes leads to a better un- derstanding of how they function. Moreover, research can provide scientific explanations to support or refute strong established beliefs of organ builders and, last but not least, can provide new scientific results and tools for further im- provement of the art of pipe organ building.
monic partials. b: Optimized design enhancing the third harmonic (pure fifth) by 15 dB. c: Optimized design enhancing the fifth (major third) by 17 dB. Numbers on the green and yellow backgrounds show the relative levels of the harmonics compared with the reference pipe.
Judit Angster is a physicist and has been working at the Fraunhofer Institute of Building Physics IBP in Stuttgart, Ger- many, since 1992. She established and has been head of the Research Group of Musi- cal Acoustics/Photoacoustics. She lectures on acoustics at the University of Stuttgart
and the State University of Music and Performing Arts Stutt- gart. Her research activities are focused on musical acoustics, music and room, pipe organ acoustics, and photoacoustics. She organizes organ acoustics workshops as an international advanced training for organ builders and organ experts. She comes from the well-known organ builder family Angster.
Péter Rucz is an electrical engineer whose main interests are musical and numerical acoustics and digital signal processing. He obtained his diploma (MS) and PhD in electrical engineering at the Budapest University of Technol- ogy and Economics, Budapest, Hungary.
Currently, Péter is a researcher at the Laboratory of Acous- tics and Studio Technologies at the same university.
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