Nonlinear Structuring of Helmholtz Resonators for Increasing the Range of Sound Absorption
ENTPE, Universiť de Lyon
Tuesday 2 june, 2015, 08:40 - 09:00
0.7 Lisbon (47)
The common way to solve the problem of sound absorption and control is to combine optimized acoustic absorbers, typically foams, wools, perforated plates, or honeycombs, in multilayered structures. But porous materials suffer from a lack of absorption at low frequencies when compared to their efficiency at higher frequencies. At low frequencies, typically below 1000 Hz, a porous material stands in the viscous regime resulting in a low absorption property. Furthermore, increasing the thickness and the mass of the structure is usually impossible for practical applications. One of the best current technologies for damping low frequencies resonances consists in a coupling of the place to be treated, with another resonating system used as absorber, known as Frahm dampers or Helmholtz resonators. The drawback of these systems is that they are valid and tuned for a very narrow frequency range. The geometry of the neck of Helmholtz resonators plays an important role in the quality and the range of noise absorption. In this work we will presents a novel structured geometry of Helmholtz resonators and by treating system analytically and numerically we will show the efficiency of the structured neck. Finally analytically and numerical developments will be accompanied by experimental results.
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