| Fri September 1st 2023 11:00 – 12:30 ZH286 | Seminar | Why an organ pipe sounds longer than it actually is Leo van Hemmen |
Details:In 1860 Helmholtz published a famous paper describing the eigenmodes and eigenfrequencies of a cylindrical open organ flue pipe. Not only did he incorporate the underlying physics but also the ensuing mathematics. The only trouble was, as neatly pointed out by the famous French organ builder Cavaillé-Coll in the very same year 1860, that the actual fundamental frequency is lower than the one predicted by his theory: For an organ pipe of length L, two anti-nodes at the end with half a wavelength in between give L = λ/2 but an organ pipe “in action” sounds lower and, hence, “longer” than it actually is. The question as to the why has tantalized organ-pipe research ever since and puzzled many scientists, starting with Rayleigh. Exactly 75 years ago Levine and Schwinger published an intricate paper, a true tour-de-force, that seemed to present a breakthrough in that the end correction was computed to be 0.61 a where a is the radius of the pipe. Their method did not, however, allow a physical interpretation of their findings. Here experimental results are presented that explain why the notorious prefactor of a may well be near 0.61 and show that nevertheless the fundamental assumption of a potential flow does not hold. | ||
