The absorption of sound at oblique angles of incidence

Heyl, Paul R.; Chrisler, V. L.; Snyder, W. F.

doi:10.6028/jres.004.021

Cited by 4 publications

(3 citation statements)

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“…The impedance tube method is mainly intended for measurements under an acoustic plane wave at normal incidence. Improvements of this method so that it can measure absorption coefficients and impedance at oblique incidence were proposed, including an apparatus for prescribed incidence angles that had been suggested many years ago [28] and the more recent multi-modal decomposition method [29]. An important limitation of the impedance tube method is that the dimensions of the sample are generally small, and even if the minimum size of samples in the impedance tube have been shown to be slightly expanded [30], out-of-tube methods are generally preferred since they generally allow simpler setups and testing large samples.…”

Section: Methods For Measuring Sound Absorption At Oblique Incidencementioning

confidence: 99%

Additional Sound Absorption Within a Poroelastic Lamella Network Under Oblique Incidence

Dauchez¹,

Nennig²,

Robin³

2018

Acta Acustica united with Acustica

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To tackle the lack of efficiency of passive sound absorbing treatments in the low frequency range, a specific arrangement of a poroelastic material is proposed. Compared with the usual uniform layout, giving a lamella network structure to a material provides additional sound absorption below the quarter wavelength resonance frequency at oblique incidence. This is demonstrated experimentally on a sample made of melamine foam lamellas. A numerical approach that incorporates geometric periodicity highlights the mechanisms involved in this additional dissipation, achieved by combining structural and viscous dissipation within the lamellas. The shear and bending resonances of the lamellas can be excited at oblique incidence. The frequency of the shear resonance is related to the thickness of the sample, whereas the bending resonance is also a function of the width of the lamellas. These simple dimensional parameters allow adjustable tuning of the associated frequencies at which additional sound absorption can be obtained.

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Section: Methods For Measuring Sound Absorption At Oblique Incidencementioning

confidence: 99%

Additional Sound Absorption Within a Poroelastic Lamella Network Under Oblique Incidence

Dauchez¹,

Nennig²,

Robin³

2018

Acta Acustica united with Acustica

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“…1,2 Two standardized methods are followed to measure the properties of sound-absorbing materials, and both were initially proposed nearly a century ago. [3][4][5][6][7][8][9] The first is the impedance tube method [10][11][12][13] and the second is the reverberation chamber method. 14,15 Regarding the impedance tube, many improvements have been proposed to the early twentiethcentury standing wave tube apparatus.…”

Section: Introductionmentioning

confidence: 99%

“…1,2 Two standardized methods are followed to measure the properties of sound-absorbing materials, and both were initially proposed nearly a century ago. 3–9 The first is the impedance tube method 10–13 and the second is the reverberation chamber method. 14,15…”

Section: Introductionmentioning

confidence: 99%

Estimation of acoustical materials sound absorption coefficient under oblique incidence plane wave and diffuse field via Allard model inversion

Sciard,

Berry,

Sgard

et al. 2024

Building Acoustics

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A technique for estimating the sound absorption of materials under oblique incidence plane wave and diffuse field excitations is proposed. It requires a mobile loudspeaker and a pair of fixed microphones above a layer of absorbing material. Starting from sound pressure measurements made above the material surface for multiple source positions and by inverting Allard’s propagation model, the proposed method allows for the identification of two effective (or equivalent) parameters, namely, the complex effective density and the complex wave number. Obtaining these parameters makes it possible to estimate the sound absorption coefficient for a plane wave with any angle of incidence or under a diffuse acoustic field by summation over the angles. The results are compared to theoretical values calculated using the Johnson-Champoux-Allard model and to reference measurements obtained using an impedance tube, a small cabin, a large reverberant room, and a sound field synthesis method. One of the limitations of this method lies in the assumptions associated with the Allard model to describe the sound field above the material (assumed to be isotropic, homogeneous, of constant thickness, and to behave like an equivalent fluid). The main advantages are (1) that the sound absorption coefficient can be estimated under oblique incidence plane wave and diffuse acoustic field with values that are always in a physical range (between 0 and 1), and (2) that samples of the order of the square meter without specific preparation can be tested which reduces the constraints associated with impedance tube or reverberant room measurements.

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Die Schallschluckstoffe

Skudrƶyk

1954

Die Grundlagen Der Akustik

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The absorption of sound at oblique angles of incidence

Cited by 4 publications

References 0 publications

Additional Sound Absorption Within a Poroelastic Lamella Network Under Oblique Incidence

Additional Sound Absorption Within a Poroelastic Lamella Network Under Oblique Incidence

Estimation of acoustical materials sound absorption coefficient under oblique incidence plane wave and diffuse field via Allard model inversion

Die Schallschluckstoffe

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