Search results for "Sound absorption"
showing 9 items of 9 documents
Experimental investigation of the effect of moisture on the acoustic properties of lightweight substrates used in green envelopes
2021
International audience; Substrates are used in green walls and roofs to supply air and water to the roots of the growing plants. These substrates are porous with micropores which store water and macropores which facilitate drainage and air entry. Effect of moisture on acoustic absorption is studied for two lightweight substrates: coir dust and perlite. Measurement of dry and moistened substrates are conducted to evaluate their effective speed of sound, attenuation, characteristic impedance, compressibility and density between 100 Hz and 1000 Hz using an impedance tube and the three microphone-two load method. Effect of moisture on these quantities is found to depend strongly upon the intera…
Enhancing the sound absorption of small-scale 3D printed acoustic metamaterials based on Helmholtz resonators
2018
Acoustic metamaterials have recently become of interest for their ability to attenuate sound by breaking the mass-density law. In this paper, acoustic metamaterials based on Helmholtz resonators and capable of attenuating sound up to 30 dB are fabricated for sound absorption applications in the small scale. The proposed metamaterials are subwavelength at a factor of $\lambda /12$ with respect to the lateral dimension of the units. The directional response due to the position of the acoustic source on the sound attenuation provided by the metamaterial is investigated by controlling the location of a loudspeaker with a robot arm. To enhance and broaden the absorption bands, structural modific…
New Acoustic Test Chambers at the University of Palermo
2008
Acoustic test chambers at the University of Palermo have been completed after a design optimization of existent building structures. A unique building houses five reverberation chambers, differently coupled each other in order to achieve a large flexibility on testing procedures, and offices for the staff. Main measurements offered to national and international standards include determination of sound power, sound insulation and sound absorption. Reverberation chambers present peculiar geometries in order to achieve the desidered sound fields. Chambers structure and layout within the whole building, housing all the acoustic facilities, has been designed in order to achieve strong sound insu…
Sound absorption prediction of linear damped acoustic resonators using a lightweight hybrid model
2019
International audience; A lightweight numerical method is developed to predict the sound absorption coefficient of resonators whose cross-section dimensions are significantly larger compared to the viscous and thermal boundary layer’s thicknesses. This method is based on the boundary layer theory and on the perturbations theory. According to the perturbations theory, in acoustical domains with large dimensions, the fluid viscosity and thermal conductivity only affect the boundary layers. The model proposed in this article combines the lossless Helmholtz wave equation derived from a perfect fluid hypothesis, with viscosity and thermal conductivity values of a real fluid to compute the sound …
Mechanical and acoustical behavior of sugarcane and flax fibres reinforced biocomposite
2017
For reasons of comfort, modern constructions require acoustic and thermal insulating materials, offering good mechanical performances. In this context, the valorization of plant fibres from the agro-food industry presents economic and environmental benefits. Thus, the aim of the present study is to develop a multifunctional sugarcane fibres reinforced epoxy porous composite combining good acoustic and mechanical properties.The study of the bagasse fibres geometry has shown that fibres’ length and diameter distribution can be fitted by lognormal laws. Composites manufactured by thermocompression process with an epoxy matrix were characterized using an experimental design whose parameters wer…
Recent developments in the acoustical properties of perforated and porous materials containing dead-end pores
2017
It was shown recently in Nevers, France, Sherbrooke, Canada and Salford, UK, that porous materials with semi-opened pores or materials with open pores bearing lateral cavities or resonators at the microscopic scale of the pores can result in peculiar sound absorption properties. Various examples of these materials can be found in engineering and in everyday life including bio-based materials. The cavities and resonators can be assimilated to dead-end pores, which are opened at one end and closed at the other. The dead-end pores are known to geophysicists. We studied them more recently in the field of engineering acoustics where the saturating fluid is air. The closed ends prevent the fluid …
Acoustic properties of plates with unevenly distributed macro perforations backed by woven meshes
2012
A hybrid model describing the acoustic properties of plates with macro-perforations that can be unevenly distributed on the plate surface and backed by woven or precision woven meshes with microscopic perforations is proposed. The plate perforations may be of circular or rectangular shapes. Since the perforated plate may not necessarily be considered as an equivalent fluid, its surface impedance is calculated by the Maa model [Noise Control Eng. J. 29, 77-84 (1987)], whereas the Johnson-Champoux-Allard model [J. Appl. Phys. 70, 1975-1979 (1991)] is used for the mesh. It is observed that the absorption of the carrying plate seems to depend on the hydraulic diameter of the perforations and no…
On the measurement and prediction of the sound absorption coefficient of air-cavity backed perforated plates considering the holes interaction effect…
2012
International audience; This paper deals with the measurement and prediction of air cavity backed perforated plates considering the holes interaction effect under relatively low sound excitation. A revised expression for the radiation contribution is proposed to properly account for the holes interaction effect. This expression is integrated in the characteristic impedance expression following Atalla and Sgard [J. Sound Vib. 303, 195-208 (2007)] model. Perforated plate specimens with different centre-to-centre holes distances (pitches) are built and tested using an impedance tube. The particular cases of holes interaction effect with constant low porosity and of holes interaction effect wit…
Sound absorption coefficient of a porous material covered with a low open area perforated plate under high sound excitation
2012
International audience; The sound absorption coefficient of porous materials covered with low open area perforated plate is studied under high sound intensities in the absence of mean flow. The theoretical considerations are based on the equivalent fluid following the Johnson-Champoux-Allard approach and the use of the transfer matrix method. To take into account the high sound levels effects, the air flow resistivity of each layer is modified following the Forchheimer law. Two specimens of perforated plate are built and tested when backed by a polymeric foam and a fibrous material. A specific impedance tube setup is developed for the measurement of the surface acoustic impedance for sound …