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Sound absorption and transmission through flexible micro-perforated structures
Áreas de investigación
  • Ingeniería civil y arquitectura
Soundproof structures made of single and multiple-layer Micro-Perforated Panels (MPPs) have proved efficient to improve acoustical comfort, speech intelligibility and comply with lightweight, transparency and fibreless requirements. Increasing applications are found in architectural acoustics or in the aeronautic and surface transport industries.1-2 A large research effort has been devoted to study the absorption properties of MPP resonance absorbers backed by a rigid wall.3-4 The shear forces due to the increase of particle velocity through the MPPs sub-millimeter holes dissipate the acoustical energy and can create relative wide-band absorbers without any additional layer of porous materials to be effective. To widen the effective bandwidth without altering the maximum absorption value, the combination of multiple MPPs has been proposed.5-6 Most of these analyses have been developed considering MPPs as rigid structures of infinite extent. However, experimental evidence of the influence of the vibrating response of thin MPPs has been found that show the strong effect of panels structural modes on the MPP acoustic performance, as unexpected absorption peaks appear in the low frequency range.7-10 Recently, Bravo et al.9 have presented results to determine how the sound absorption properties of rigidly-backed MPPs are modified by the vibrating response of the perforated facing. The extra peaks or dips appearing in the absorption coefficient have been classified as panel-controlled or hole-cavity-controlled resonances of the panel-hole-cavity system, depending on whether the effective air mass of the perforations is greater or lower than the panel first modal mass. Also, the absorption coefficient is often considered as the only parameter indicating the performance of the device. Few studies on MPPs acoustical performances address both absorption and transmission problems.11-12 Recently, Dupont et al.11 have used a transfer matrix approach that couples a MPP with an infinite flexible plate to model the absorption and the transmission properties. They have shown that inclusion of a vibrating back panel to the MPP alone increases the Transmission Loss (TL) of the partition, significantly reduces reflections and weakens the coincidence effect. Toyoda and Takahashi12 have developed a theoretical model for the absorption and the TL of a double-leaf MPP structure backed by an elastic wall, assuming systems of infinite extent. The air-cavity subdivision technique can be achieved by inserting a honeycomb layer within the cavity. It has proved to be efficient for improving both absorption and transmission performances at mid-frequencies.12-13 Indeed, the subdivisions provide normal absorption conditions inside each core cell, therefore enhancing acoustical dissipation within the whole system. If the subdivisions are glued to the facings, maximum absorption is increased with respect to the unglued case albeit at the expense of the transmission loss which degrades around the mass-air-mass resonance, but still stays higher than the TL obtained with the full air cavity. It is the aim of the present work to develop and validate a fully coupled model to describe sound absorption and transmission through multi-layer MPPs and that accounts for both finite-size and elasticity effects of the panel. A fully coupled modal approach is proposed to calculate the absorption coefficient and the TL of finite-sized layouts made up of flexible panels, including MPPs. Validation results are presented for a single-layer MPP device against measurements performed in an anechoic chamber. Specific relationships are experimentally observed on the air-frame relative velocity over the MPP surface around the Helmholtz-type and the structural resonance frequencies of the MPP layout. Principled guidelines are provided for enhancing both the sound absorption and transmission properties of such MPP structures through suitable setting of the design parameters.
Nombre congreso
ICA 2013
Tipo de participación
Lugar del congreso
Montreal, Canada
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Título de las actas
Proceedings of Meetings on Acoustics, Volume 19
Esta actividad pertenece a memorias de investigación
  • Autor: Teresa Bravo Maria (UPM)
Grupos de investigación, Departamentos, Centros e Institutos de I+D+i relacionados
  • Creador: Departamento: Física e Instalaciones Aplicadas a la Edificación, al Medio Ambiente y al Urbanismo
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