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Journal ArticleDOI

Acoustic performance of countersunk micro-perforated panel in multilayer porous material:

L. Yuvaraj1, S. Jeyanthi1
01 Mar 2020-Building Acoustics (SAGE PublicationsSage UK: London, England)-Vol. 27, Iss: 1, pp 3-20
TL;DR: In this article, the acoustic performance of a countersunk micro-perforated panel, along with two distinct porous materials used in a multilayer porous absorber configuration, was investigated.
Abstract: This study investigates the acoustic performance of a countersunk micro-perforated panel, along with two distinct porous materials used in a multilayer porous absorber configuration. Additive manuf...
Citations
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01 Jan 2000
TL;DR: In this paper, the exact formulae of the acoustical impedance of a narrow slit and its low-frequency approximation are derived and a simple and practical formula is derived for the single slit.
Abstract: It is well known that narrow slit may be used as acoustical element. The exact formulae of the acoustical impedance of a narrow slit and its low-frequency approximation are available. The theory of slit is extended and a simple and practical formula is derived for the single slit. It is found that the resistances-to-reactance ratio of the slit increases to larger than one when the slit width is decreased to submillimeter range, and a panel with extremely narrow slits plus a back cavity will make an absorber with good absorption in a wide frequency range, without any porous or fibrous material. A complete theory of the microslit absorber (MSA) is, thus, presented and its absorption characteristics are discussed. It is found that the MSA has essentially the same formulae as the microperforated absorber (MPA), except that the numerical coefficient of the resistance is smaller and the end correction for the mass reactance is larger for the MSA, resulting a performance inferior to that of MPA, ordinarily. Measures are proposed to compensate for these.

22 citations

Journal ArticleDOI
TL;DR: In this paper , a 50 mm thick meta-structure is proposed, which obtains an average sound absorption performance of 70 % from 1000 Hz to 2800 Hz, compared with a structure of the same size but without considering the acoustic critical absorption effect.

4 citations

Journal ArticleDOI
TL;DR: In this article, an acoustic structure consisting of cellular and perforated panel absorbers has been designed to noise control, and the sound absorption behavior of designed acoustic structure has been investigated experimentally by reinforcing with STFs having different rheological properties.

2 citations

Journal ArticleDOI
Ke Li1, Shengjun Li, Zhonghua Bao1, Qianqian Liu1, Tao Liu1 
TL;DR: The experimental results show that the optimization method of the parameters of the impedance gradient change medium based on reinforcement learning was superior to the traditional method and are effective to reduce the acoustic reflection to a lower level.
Abstract: Based on the relative researches, in order to solve the problem that the parameters of impedance gradient change medium are difficult to be optimized and generalized in different environments, an o...

2 citations

References
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Journal ArticleDOI

3,536 citations

Journal ArticleDOI
TL;DR: In this paper, the effect of different aperture geometries on the resonance frequency of resonators is considered and illustrated by examples, considering losses due to viscosity, heat conduction, and radiation, the optimum design for maximum resonance absorption is analyzed, and the results are expressed in terms of design charts.
Abstract: Absorption and scattering from resonators in a free field as well as in walls are discussed. The effect of different aperture geometries on the resonance frequency of resonators is considered and illustrated by examples. Considering losses due to viscosity, heat conduction, and radiation, the optimum design for maximum resonance absorption is analyzed, and the results are expressed in terms of design charts. Nonlinear effects on the absorption and resonance frequency are also included, and a discussion of the onset of turbulence is presented.

751 citations

Journal ArticleDOI
TL;DR: In this paper, new expressions are given that can be used instead of the phenomenological equations of Delany and Bazley, and they provide similar predictions in the range of validity of these equations, and in addition are valid at low frequencies where the equations provided unphysical predictions.
Abstract: New expressions are given that can be used instead of the phenomenological equations of Delany and Bazley. They provide similar predictions in the range of validity of these equations, and in addition are valid at low frequencies where the equations of Delany and Bazley provide unphysical predictions. These new expressions have been worked out by using the general frequency dependence of the viscous forces in porous materials proposed by Johnson et al. [J. Fluid Mech. 176, 379 (1987)], with a transposition carried out to predict the dynamic bulk modulus of air. The model used suggests how sound propagation in fibrous materials can depend both on the diameter of the fibers and on the density of the material.

493 citations

Journal ArticleDOI
TL;DR: In this article, a study of the behavior of the acoustic impedance of a range of perforates at medium and high incident sound pressure levels was carried out, which included a detailed experimental programme together with a theoretical analysis of the problem.

392 citations

Journal ArticleDOI
TL;DR: In this paper, the authors used smoke particles in a 3.5-in. diameter circular tube to study acoustical streaming phenomena around orifices, showing that there exist four definite regions of flow as the particle velocity in the orif.
Abstract: In his theory of streaming caused by sound waves, Eckart shows that time independent streams necessarily follow as part of the solution of the complete wave equatoin, taking into account viscosity and second‐order terms. His treatment is mainly valid for liquids and it proves that the driving force of the streams is proportional to frequency squared. The effect, therefore, is especially important in the ultrasonic region (crystal winds). However, he suggests that slow streams might also be carried in air at audio frequencies.Studies of acoustical streaming phenomena around orifices have been made by the use of smoke particles in a 3‐in. diameter circular tube. These studies covered a range of orifices from thicknesses of 0.5 mm to 19 mm and diameters of 3.5 mm to 20 mm. The frequency lay between 150 to 1000 c.p.s. Velocities in the orifice cover the range of 0 to 700 cm/sec.Close studies of the flow patterns have disclosed that there exist four definite regions of flow as the particle velocity in the orif...

358 citations