Celse K. Amédin

Reproducibility experiments on measuring acoustical properties of rigid-frame porous media (round-robin tests)

This paper reports the results of reproducibility experiments on the interlaboratory characterization of the acoustical properties of three types of consolidated porous media: granulated porous rubber, reticulated foam, and fiberglass. The measurements are conducted in several independent laboratories in Europe and North America. The studied acoustical characteristics are the surface complex acoustic impedance at normal incidence and plane wave absorption coefficient which are determined using the standard impedance tube method. The paper provides detailed procedures related to sample preparation and installation and it discusses the dispersion in the acoustical material property observed between individual material samples and laboratories. The importance of the boundary conditions, homogeneity of the porous material structure, and stability of the adopted signal processing method are highlighted.

On the modeling of sound radiation from poroelastic materials

Numerical approaches based on finite element discretizations of Biot’s poroelasticity equations provide efficient tools to solve problems where the porous material is coupled to elastic structures and finite extent acoustic cavities. Sometimes, it may be relevant to evaluate the radiation of a poroelastic material into an infinite fluid medium. Examples include (i) the evaluation of the diffuse field sound absorption coefficient of a porous material and/or the sound transmission loss of an elastic plate coupled to a porous sheet, (ii) the assessment of the acoustic radiation damping of a porous material coupled to a vibrating structure. The latter is particularly important for the correct experimental characterization of the intrinsic damping of the material’s frame. Up to now, the acoustic radiation of a porous medium into an unbounded fluid medium has usually been neglected. The classical approaches for modeling free field radiation of porous materials (i) assumes the interstitial pressure at the radiation surface to be zero or (ii) fixes the radiation impedance to an approximate value. This paper discusses the limitations of these assumptions and presents a numerical formulation for evaluating the sound radiation of baffled poroelastic media including fluid loading effects. The problem is solved using a mixed FEM-BEM approach where the fluid loading is accounted for using an admittance matrix. Both numerical examples and a transmission loss test are presented to illustrate the performance of the technique and its applications.

Acoustical characterization of absorbing porous materials through transmission measurements in a free field

Various results are presented to experimentally validate the theoretical modeling of the acoustic radiation of a circular piston through a thin layer of porous absorbing material, as worked out by Amedin et al. [J. Acoust. Soc. Am. 98, 1757–1766 (1995)]. This theoretical modeling is subsequently exploited for the development of an acoustical characterization method for porous absorbing materials. The method is based on acoustical pressure measurements taken at two different positions in an open baffled tube radiating into the material to be characterized and at a given point above the material, and on an iterative process of numerical resolution. The reliability of the method is evaluated by means of numerical simulations and by comparisons using the two-layer method in an impedance tube [J. Acoust. Soc. Am. 74, 1577–1582 (1983)]. The preliminary tests show that the new method can be used to experimentally characterize the specific acoustic impedance and the propagation constant of porous absorbing materi...

How reproducible is the acoustical characterization of porous media

There is a considerable number of research publications on the characterization of porous media that is carried out in accordance with ISO 10534-2 (International Standards Organization, Geneva, Switzerland, 2001) and/or ISO 9053 (International Standards Organization, Geneva, Switzerland, 1991). According to the Web of ScienceTM (last accessed 22 September 2016) there were 339 publications in the Journal of the Acoustical Society of America alone which deal with the acoustics of porous media. However, the reproducibility of these characterization procedures is not well understood. This paper deals with the reproducibility of some standard characterization procedures for acoustic porous materials. The paper is an extension of the work published by Horoshenkov, Khan, Bécot, Jaouen, Sgard, Renault, Amirouche, Pompoli, Prodi, Bonfiglio, Pispola, Asdrubali, Hübelt, Atalla, Amédin, Lauriks, and Boeckx [J. Acoust. Soc. Am. 122(1), 345-353 (2007)]. In this paper, independent laboratory measurements were performed on the same material specimens so that the naturally occurring inhomogeneity in materials was controlled. It also presented the reproducibility data for the characteristic impedance, complex wavenumber, and for some related pore structure properties. This work can be helpful to better understand the tolerances of these material characterization procedures so improvements can be developed to reduce experimental errors and improve the reproducibility between laboratories.

Prediction of the acoustical performance of enclosures using a hybrid statistical energy analysis: image source model.

Enclosures are commonly used to reduce the sound exposure of workers to the noise radiated by machinery. Some acoustic predictive tools ranging from simple analytical tools to sophisticated numerical deterministic models are available to estimate the enclosure acoustical performance. However, simple analytical models are usually valid in limited frequency ranges because of underlying assumptions whereas numerical models are commonly limited to low frequencies. This paper presents a general and simple model for predicting the acoustic performance of large free-standing enclosures which is capable of taking into account the complexity of the enclosure configuration and covering a large frequency range. It is based on the statistical energy analysis (SEA) framework. The sound field inside the enclosure is calculated using the method of image sources. Sound transmission across the various elements of the enclosure is considered in the SEA formalism. The model is evaluated by comparison with existing methods and experimental results. The effect of several parameters such as enclosure geometry, panel materials, presence of noise control treatments, location of the source inside the enclosure, and presence of an opening has been investigated. The comparisons between the model and the experimental results show a good agreement for most of the tested configurations.

Sound field of a baffled piston source covered by a porous medium layer

Two models for the prediction of sound transmission through a thick layer of material which lies on a horizontal baffle are presented. These models are a preliminary investigation of a method for the acoustical and physical characterizations of porous materials. The acoustic source is assumed to be a circular, baffled piston source mounted under a layer of porous material. The sound is transmitted through the porous layer to the semi‐infinite half‐space above the layer. The models are used to calculate the transfer function between the volume velocity of the source and the sound pressure above the porous material. The first model is based on the integral method in which appropriate Green’s functions are used to describe the sound field, and on a collocation procedure. The second model uses a method of decomposition of the sound field into cylindrical waves. The numerical results of the two models are in good agreement. A significant sensitivity of the transmitted sound field to the material’s physical cha...

Sound transmission through multilayer structures with isotropic elastic porous materials

This paper discusses the prediction of transmission loss through multilayer structures with porous materials. First, a brief review of recent formulations for multilayer structures with poroelastic materials is presented. Second, the transmission loss problem is described and formulated using a coupled finite element and boundary element procedure. Issues such as poroelastic‐elastic coupling, poroelastic‐fluid coupling, and radiation from a poroelastic material will be addressed. The developed model is validated through numerical examples. Its advantages and limitations are discussed. Finally, typical results showing the vibroacoustic effects of several parameters such as the multilayer configuration, the types of porous materials, and the mounting conditions are presented. [Work supported by Bombardier, Inc., Canadair and N.S.E.R.C.]

A hybrid SEA/image sources approach for the prediction of the insertion loss of enclosures

Enclosures are a classical solution to reduce the sound exposure of workers to the noise radiated by machinery. Their acoustic design can be achieved with the help of predictive tools based on simple analytical tools or sophisticated numerical deterministic models. However, there is no simple and fast tool allowing to account for the complexity of the enclosure configuration, capable of better simulating the non‐diffuse nature of the field inside the enclosure and covering the typical frequency range [100Hz; 5000Hz]. This paper presents the development of such a tool for the prediction of the acoustic performance of enclosures. It is based on a hybrid model: the statistical energy analysis (SEA) for the sound transmission across the various elements of the enclosure and the method of image sources for the sound field inside the enclosure. The approach is validated by comparing calculation and experimental results carried out in a semi‐anechoic room on rectangular and L‐shape enclosures for several inner s...

A transmission method for estimating the specific acoustic impedance of a porous material: Modelization

A new method is suggested for the characterization of porous materials; it is based on a measurement of the sound transmission through a layer of the material. This paper presents two theoretical models to evaluate the potential of the method. In these models, a thin layer of the material lies on a horizontal baffle; the acoustic source is a waveguide mounted vertically under the baffle with its end flush to the baffle and the sound is transmitted through the layer to the half‐space above the layer. The two models calculate the transfer function between the volume velocity of the waveguide and the sound pressure over the layer. The first model is based on the integral method and collocation in which the appropriate Green’s functions are used to describe the sound field. The second model uses a method of decomposition into plane waves. The details of each model are described; results, comparisons, and validations are presented. Finally, the potential of the method to evaluate the characteristics of the por...

Integral method for modeling the sound field above a porous material

A new concept of a transmission technique for the characterization of porous material is presented. It is based on the accurate modeling of the sound field above the layer of material that rests on an horizontal infinite baffle. The sound field is generated by a waveguide mounted vertically under the baffle with its termination flush to the baffle. The waveguide is assumed to create a uniform distribution of particle velocity at the termination. The field in the material is expressed using a Green’s function that accounts for the multiple reflections on the baffle and at the upper surface of the material. The field above the material is formulated in terms of the pressure gradient distribution over the upper surface. Starting with the boundary conditions at the upper surface (continuity of the sound pressure and normal particle velocity), the collocation method is used to solve for the pressure gradient at a mesh on this surface. This, in turn, allows one to calculate the sound pressure above the material...