Microstructures for lowering the quarter wavelength resonance frequency of a hard-backed rigid-porous layer

Abstract

The Open University's repository of research publications and other research outputs Microstructures for lowering the quarter wavelength resonance frequency of a hard-backed rigid-porous layer Journal Item How to cite: Attenborough, Keith (2018). Microstructures for lowering the quarter wavelength resonance frequency of a hard-backed rigid-porous layer. Applied Acoustics, 130 pp. 188-194. For guidance on citations see FAQs.

Macro- and micro-structure designs for porous sound absorbers

“…The sound absorption of a dual-porosity arrangement involving two different widths of orthogonal intersecting uniform slits has been considered previously [10]. Such an arrangement is predicted to result in low-Q quarter wavelength layer resonance.…”

“…Considerable efforts have been made to relate such parameters to pore structure, thereby, improving understanding of the influence of pore structure on acoustical performance [7] and of what to control during the manufacturing process [9]. On the other hand, simple pore structures are predicted to yield absorption spectra comparable with, or, indeed, better than those achieved with bulk manufactured materials [10].…”

“…Previously the acoustical performances of rigid-framed media containing identical uniform pores inclined to the surface, sinusoidally-sided slits, annular cylindrical pores and slit arrays with two significantly-different cross sections (dual porosity) have been considered separately and in combination [10]. These pore structures increase tortuosity thereby increasing the effective path length and reducing the sound speed through the hard-backed layer.…”

“…So far, however, not much use has been made of knowledge about the influence of pore structure on acoustical properties. For example, the changes in absorption observed with pore inclination in perforated samples manufactured by 3D printing [12] are predictable [10]. Moreover, macro-structural effects have not been considered.…”

“…In principle, subject to the constraints of additive manufacturing processes [14], it should be possible to devise internal structures at macro-and micro-scales that realise any desired sound absorption performance. After revising a model for the acoustical properties of arrays of parallel, uniform, identical slits, previous work [2][3][4]10] is extended by predicting the absorption spectra yielded by impedance matching, periodic non-uniformity and partitioning in simple slit-pore structures.…”