Experimental and numerical investigation on aerosols emission in musical practice and efficiency of reduction means.

Early in the CoViD-19 pandemic, musical practices, especially singing and playing wind instruments, have been pointed out as having a high risk disease transmission due to aerosol production. However, characterization of these emission sources was not consolidated. This study focuses on the generation of aerosols and potential reduction in the context of playing wind instruments and singing. Aerosol concentration reduction means are evaluated using aerosol measurements in clean room and Computational Fluid Dynamics. Measurements at the bell of a clarinet and in front of singers are performed with or without a protection (bell cover for clarinet and surgical mask for singers). Numerical results on clarinet suggest that most of the supermicron ( ≥ 1 µ m ) particles are trapped on the walls of the instruments, which act as a filter, depending on toneholes configurations (closed or opened) changing the frequency of sound produced. Experimental results are consistent since almost only submicron particles contribute to the measured number concentration during playing clarinet. First of all, the high inter and intra-individuals variability is highlighted, with high coefficients of variation. This study highlights the impact of fingerings on the generated particles and the efficiency of protections such as bell cover (from 3 to 100 times), depending on the played note and players. Results for singers show that surgical masks significantly reduce the aerosol concentration (from 8 to 170 times) in front of the mouth. The evolution of aerosol concentration is also correlated with sound intensity.

The dual influence of the reed resonance frequency and tonehole lattice cutoff frequency on sound production and radiation of a clarinet-like instrument.

The internal and external spectra of woodwind reed instruments are partially determined by the tonehole lattice cutoff and reed resonance frequencies. Because they can impact the spectrum in similar ways, a study of one without accounting for the other risks incomplete or false conclusions. Here, the dual effects of the cutoff and reed resonance frequencies are investigated using digital synthesis with clarinet-like academic resonators. It is shown that the odd and even harmonics have similar amplitudes at and above the cutoff frequency or reed resonance frequency, whichever is lowest. However, because the resonators radiate efficiently at the cutoff, it has the additional role of reinforcing the amplitude of both the odd and even harmonics in the external spectrum. The spectra are analyzed using the single value descriptors playing frequency, spectral centroid (SC), odd/even ratio (OER), and brightness as a function of the musician mouth pressure. Higher reed resonances correspond to higher values for all descriptors. The OER and brightness increase with resonator cutoff frequency, whereas the SC exhibits more complicated trends. The reed resonance has a larger impact on the "playing condition oscillation threshold," implying that it may have a more important role in sustaining auto-oscillation.

Woodwind instrument design optimization based on impedance characteristics with geometric constraints.

Computational optimization algorithms coupled with acoustic models of wind instruments provide instrument makers with an opportunity to explore new designs. Specifically, they enable the automatic discovery of geometries exhibiting desired resonance characteristics. In this paper, the design optimization of woodwind instruments with complex geometrical features (e.g., non-cylindrical bore profile and side holes with various radii and chimney heights) is investigated. Optimal geometric designs are searched so that their acoustic input impedance has peaks with specific target frequencies and amplitudes. However, woodwind instruments exhibit complex input impedance whose features, such as resonances, might have non-smooth evolution with respect to design variables, thus hampering gradient-based optimization. For this reason, this paper introduces new formulations of the impedance characteristics (resonance frequencies and amplitudes) using a regularized unwrapped angle of the reflection function. The approach is applied to an illustrative instrument subjected to geometric constraints similar to the ones encountered by manufacturers (a key-less pentatonic clarinet with two-registers). Three optimization problems are considered, demonstrating a strategy to simultaneously adjust several impedance characteristics on all fingerings.