International audienceIncandescent filaments and membranes are often used as infrared sources despite their low efficiency, broad angular emission, and lack of spectral selectivity. Here, we introduce a metasurface to control simultaneously the spectrum and the directivity of blackbody radiation. The plasmonic metasurface operates reliably at 600 °C with an emissivity higher than 0.85 in a narrow frequency band and in a narrow solid angle. This emitter paves the way for the development of compact, efficient, and cheap IR sources and gas detection systems
This paper presents experimental results that quantify the range of influence of vocal tract manipulations used in saxophone performance. The experiments utilized a measurement system that provides a relative comparison of the upstream windway and downstream air column impedances under normal playing conditions, allowing researchers and players to investigate the effect of vocal-tract manipulations in real time. Playing experiments explored vocal-tract influence over the full range of the saxophone, as well as when performing special effects such as pitch bending, multiphonics, and "bugling." The results show that, under certain conditions, players can create an upstream windway resonance that is strong enough to override the downstream system in controlling reed vibrations. This can occur when the downstream air column provides only weak support of a given note or effect, especially for notes with fundamental frequencies an octave below the air column cutoff frequency and higher. Vocal-tract influence is clearly demonstrated when pitch bending notes high in the traditional range of the alto saxophone and when playing in the saxophone's extended register. Subtle timbre variations via tongue position changes are possible for most notes in the saxophone's traditional range and can affect spectral content from at least 800-2000 Hz.
A method is proposed to determine the transfer matrix parameters of a discontinuity in a waveguide with the finite element method (FEM). This is used to characterize open and closed woodwind instrument toneholes and develop expressions for the shunt and series equivalent lengths. Two types of toneholes are characterized: Unflanged toneholes made of thin material, such as found on saxophones and concert flutes, and toneholes drilled through a thick material, such as found on most instruments made of wood. The results are compared with previous tonehole models from the literature. In general, the proposed expressions provide a better fit across a wide range of frequencies and tonehole sizes than previous results. For tall toneholes, the results are in general agreement with previous models. For shorter tonehole heights, some discrepancies from previous results are found that are most important for larger diameter toneholes. Finally, the impact of a main bore taper (conicity) on the characterization of toneholes was investigated and found to be negligible for taper angles common in musical instruments.
The classical Transfer-Matrix Method (TMM) is often used to calculate the input impedance of woodwind instruments. However, the TMM ignores the possible influence of the radiated sound from toneholes on other open holes. In this paper a method is proposed to account for external tonehole interactions. We describe the Transfer-Matrix Method with external Interaction (TMMI) and then compare results using this approach with the Finite Element Method (FEM) and TMM, as well as with experimental data. It is found that the external tonehole interactions increase the amount of radiated energy, reduce slightly the lower resonance frequencies, and modify significantly the response near and above the tonehole lattice cutoff frequency. In an appendix, a simple perturbation of the TMM to account for external interactions is investigated, though it is found to be inadequate at low frequencies and for holes spaced far apart.
The problem of the junction between a cylinder and a truncated cone at frequencies below the first cutoff of the cylinder is investigated, in particular for the case of acute angles. An analytical model of the matching of a cylinder and a truncated cone is derived for the general case of a cone of finite length having a known terminal impedance. When the cone is infinite and the angle is right, the problem is similar to the classical problem of a tube radiating in an infinite baffle. The model is based on a general formulation of the junction of several waveguides at low frequencies (when only the fundamental mode propagates in each guide), and on the assumption that at high frequencies, the radiation impedance of the cylinder is equal to its characteristic
Recent investigations are presented for the measurement of acoustic input impedance of wind music instruments. Initial efforts have focused on measurements of alto saxophones using a two-microphone, three-calibration tube procedure. We first present the design of the impedance probe, as well as the data sampling and analysis procedures. We then discuss the relationship between errors in the calculated calibration parameters and the resulting measured transfer functions. Finally, we compare the input impedances of Yamaha Z and Selmer Series II alto saxophones for several low register fingerings. We note several instances where the Yamaha saxophone possesses significantly stronger fundamental resonances than the Selmer saxophone.
The two-microphone technique with a broadband excitation has been used for the measurement of various objects including straight conical waveguides and alto saxophones. An improved procedure has been developed whereby the noise excitation signal is pre-filtered by the inverse frequency response of the system under consideration. This approach helps reduce distortion and improves the SNR of the measurement. Results with and without pre-filtering are compared for different fingerings of an alto saxophone. The input impedance of a straight conical waveguide is compared with theory and discrepancies are analyzed. The input impedance of saxophones are evaluated with the transmission matrix approach and compared with measurements. A software environment for efficient comparison and analysis of measurement data with theoretical calculations is presented. We also propose a framework for sharing raw measurement data among researchers to allow comparison of results obtained with different apparatus on similar objects to better quantify their accuracy.
A new approach for the analysis of vocal-tract influence in single-reed woodwind instruments during performance was recently reported (Scavone et. al., 2008). Two types of vocal-tract influence were observed. When the downstream air column provides only weak support of a given note, players can use a strong and narrow-bandwidth upstream resonance to override the reed vibrations, such as when pitch bending or playing extended register notes. Performers can also use a more wide-bandwidth upstream resonance to affect subtle timbre variations when playing notes over the full range of the instrument. The research reported here addresses the performance of multiphonic tones, for which the results of the previously mentioned study were less conclusive. While it is clear that upstream influence is involved in the production of multiphonics, we are interested in determining whether performers must support a specific intermodulation component or a wider bandwidth range of components for proper production. The latest results of this research will be reported.
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