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1
Content available The cello sound generation mechanism in vibroacoustic studies of the impact of the endpin material on the cello sound
Gorazd Łukasz, Pochel Maja
Vibrations in Physical Systems
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2023
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Vol. 34, nr 2
art. no. 2023201
EN
The aim of the paper is to present the structure of the mechanism that excites the cello strings to vibrate, used in vibroacoustic research of the impact of the endpin material on the cello sound. The construction of the device is inspired by the hurdy-gurdy mechanism. In the acoustic study of string instruments, it is hard to take into account the human factor during the generation of sound. When playing an instrument, there is difficulty in obtaining repeatability of the generated sound, especially with a large number of repetitions. The presented device is particularly useful during vibroacoustic tests of bowed string instruments. It enables the generation of continuous sound and ensures the repeatability of excitation. In addition to the description of the construction of the mechanism, vibroacoustic tests related to the determination of the influence of the cello endpin material on its timbre were also presented. The impact of the endpin material on the cello sound was determined based on measurements as well as subjective impressions of the musicians.
2
Content available Application of the scattering matrix method to evaluate acoustic mufflers properties
Gorazd Łukasz
Vibrations in Physical Systems
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2022
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Vol. 33, nr 2
art. no. 2022204
EN
The aim of the paper is to analyse acoustic reflective muffler applying the scattering matrix method. In general, the method is based on dividing the muffler/system into separate subsystems and apply the acoustic multi-ports theory to calculate the scattering matrix of each element to finally combine the results and obtain the scattering matrix of the entire system/muffler. The multi-port procedure is derived from the theory of electric networks and allows to analyse acoustic devises of complex geometry with prescribed accuracy. Based on the scattering matrix, the transmission loss was determined.
3
Content available Experimental Determination of a Reflective Muffler Scattering Matrix for Single-Mode Excitation
Gorazd Łukasz
Archives of Acoustics
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2021
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Vol. 46, No. 4
667--675
EN
The aim of the paper is to experimentally determine the scattering matrix S of an example reflective muffler of cylindrical geometry for Helmholtz number exceeding the plane wave propagation. Determining the scattering matrix of an acoustic systems is a new and increasingly used approach in the assessment of reduction of noise propagating inside duct-like elements of heating, ventilation and air conditioning systems (HVAC). The scattering matrix of an acoustic system provides all necessary information on the propagation of wave through it. In case of the analysed reflective silencer, considered as a two-port system, the noise reduction was determined by calculating the transmission loss parameter (TL) based on the scattering matrix (S). Measurements were carried out in two planes of the cross-section of pipes connected to the muffler. The paper presents results of the scattering matrix evaluation for the wave composed of the plane wave (mode (0,0)) and the first radial mode (0,1), each of which was generated separately using the self-designed and constructed single-mode generator. The gain of proceeding measurements for single modes stems from the fact that theoretically, calculation of the S-matrix does not require, as will be presented in the paper, calculation of the measurement data inverse matrix. Moreover, if single mode sound fields are well determined, it ensures error minimization. The presented measurement results refer to an example of a duct like system with a reflective muffler for which the scattering matrix S was determined. The acoustic phenomena inside such a system can be scaled by the parameter ka.
4
Content available Simulation of a single mode wave generation in cylindrical systems applying numerical methods
Gorazd Łukasz, Snakowska Anna
Vibrations in Physical Systems
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2019
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Vol. 30, nr 1
art. no. 2019118
EN
The paper presents simulations of a selected single mode generation in systems containing duct-like elements applying the finite element method (FEM). Simulations were carried out for values of the Helmholtz number exceeding the plane-wave propagation, i.e. for a multimode wave. The presented results constitute the first step to analyse propagation of the multimode wave through more complicated systems such as mufflers, even in a form of a cascade. Propagation of the incident wave in the form of a single mode greatly simplifies solutions of many problems, to mention only derivation of the transmission or the scattering matrices. The results obtained can be applied to analyse the effectiveness of attenuation of acoustic silencers or elements of heating, ventilation and air conditioning systems (HVAC) at the design stage. Results of simulations are compared with already published experimental data obtained in a measurement set-up containing the self-designed single mode synthesizer.
5
Content available Evaluation of the transmission and the scattering matrix applicability to the mufflers analysis
Snakowska Anna, Gorazd Łukasz, Jurkiewicz Jerzy
Vibrations in Physical Systems
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2019
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Vol. 30, nr 1
art. no. 2019102
EN
The analysis of the acoustical systems can be carried out based on a number of different formalisms, of which applied frequently are the transfer matrix formalism, in which the chosen state variables are the sound pressure p and the sound velocity v, and the scattering matrix formalism adopting the sound pressures p+ and p− and the sound velocities v+ and v− of waves propagating through an element in both directions. Even though, they are mathematically equivalent, i.e. there exists the unequivocal transformation from one to another there are some advantages and disadvantages in applying one or the other to analyse mufflers or other acoustic system, especially when the propagation of a multimode wave is assumed and numerical calculations are indispensable. In the paper the transformation between the formalisms has been derived and applied to analyse the phenomena at a junction between the tail pipe and the chamber and also in mufflers composed of one or two chambers. The more flexible for numerical calculations seems the scattering matrix formalism, especially when the number of propagating modes differs on both sides of a junction. On the other hand the transmission matrix formalism is suitable for analysing systems constituting a cascade. The sources of the advantages and disadvantages of both formalisms are explained. The results obtained can be helpful in the effective design of silencers with specific properties.
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