Acoustic Absorbers and Diffusers

Room acoustic modelling of textile materials hung freely in space: from the reverberation chamber to ancient churches

“…This parameter is given by the ratio between pressure and particle velocity at the boundary of the surface and, is most generally a complex number, meaning that it affects both their amplitude and phase. A derivation of the relations between Z and α is beyond the scope of the paper and can be found in one of the many textbooks on the topic (Cox and D'Antonio 2004;Kuttruff 2009). However, when Z is very similar to air impedance Z 0 = ρc (where ρ is the density and c is sound speed), α obtains the highest value, while when Z is much larger the surface is rigid and α tends to zero.…”

“…The problem is that of establishing the best way to model textile materials hung free in space. Textiles are porous sound absorbing materials whose properties are well known and understood (Cox and D'Antonio 2004;Kuttruff 2009). However, although their theoretical behaviour can be predicted with relative ease, most of the experimental data refer to materials close to walls, or draped, with very little information available on textiles hung freely in space (Ognedal 2005).…”

“…In addition, the choice of material properties is much more delicate, and can often have substantial impact on the final results. The literature provides a wealth of information about the sound absorption of many types of materials (Cox and D'Antonio 2004), but when scattering and diffusion are taken into account the amount of information is noticeably reduced and prompts a return to 'educated guessing' based on experience as the sole rule. Small differences in the way different software handle scattering also contribute to further complicating this task.…”

Inverse estimation of the non-acoustical parameters of loose granular absorbers by Simulated Annealing

“…Sound absorption dissipates sound energy into heat by viscous and thermal effects [2][3][4]. Most of sound absorbing materials are porous-type, resonator-type or mixed porous-resonator type.…”

A Transient Boundary Element Method for Acoustic Scattering from Mixed Regular and Thin Rigid Bodies

“…An alternative is to predict this dispersion using a numerical model, and the BEM is well suited to this task 27 . The speed and low cost of this approach aids prototyping of new designs, and even allows automated optimisation of treatments to be performed 28 .…”