à 15H -
Séminaire d'Erik Alan Petersen, invité par l'équipe S3AM, à suivre via le lien meet.ircam.fr/ErikPetersen
"The Tonehole Lattice Cutoff Frequency: results from theoretical, numerical, and experimental studies"
This seminar discusses the effect of the tonehole lattice cutoff frequency on internal and external sound fields of woodwind instruments. The tonehole lattice cutoff frequency is a phenomenon of woodwind instruments that can be explained by the theory of wave propagation in periodic media. Below the cutoff, a wave traveling into the lattice is evanescent and radiates predominately from the first tonehole, while above cutoff, the wave propagates in the lattice and radiates from multiple toneholes. This theory, however, is strictly valid only for infinite, lossless lattices, and the departure from geometric periodicity of real instruments hinders the direct study of the cutoff on their sound production and radiation. Here, we use simplified clarinet-like resonators with periodic tonehole lattices that are designed to have specific cutoffs while maintaining the same first resonance frequency, and therefore resemble the theoretical case more closely than do real instruments. Therefore, certain phenomena observed on sound production and radiation can be directly attributed to the cutoff of the resonator.
In order to evaluate the effect of the cutoff, we propose three studies. The first considers only the passive response of the academic resonators through the transfer function from internal acoustic pressure and flow variables to external pressure and flow variables. We show using anechoic measurements and simulations that the cutoff has a strong impact on the radiation characteristics of the resonators, particularly with respect to directivity patterns. The second project uses digital synthesis based on physical models to evaluate the effect of the cutoff on sound production. This demonstrates a connection between the cutoff and spectral characteristics of the internal pressure and flow signals. The third study uses in situ measurements of the academic resonators played by a musician using a clarinet mouthpiece to evaluate the effect of the cutoff on the radiated sound field. These results demonstrate a strong link between the cutoff and the external spectral characteristics which are supported by audio examples. The results of the three studies are largely coherent and show how the cutoff frequency helps explain the link between internal and external acoustic variables.