(a) A cavity-backed MPP absorber with a flexible boundary surface; (b) particle velocity distribution in relation to the panel velocity and the air particle velocity averaged over each hole.
(Color online) Schematic and picture of the experimental set-up used for measuring the input impedance and absorption coefficient of the MPPA.
Sound absorption coefficient of a thin MPPA: predicted assuming a rigid (gray) or an elastic (black) MPP; measured using the two-microphones method (circles).
Phasor representation of the input impedance of a thin MPPA: predicted assuming a rigid (bold gray) or a flexible (bold black) panel; measured using the two-microphones method (circles). Circles of constant absorption coefficient (thin black).
(Color online) Schematic and picture of the experimental set-up used for measuring the disk vibrating response of the MPPA using a laser scanning vibrometer.
(Color online) Measured vibrating response of the MPPA disk in relation with local maxima of the sound absorption coefficient. Comparison with the velocity predicted at the resonance frequencies of the panel-cavity volume displacing modes.
Phase difference curves between the panel averaged velocity and the air particle velocity induced by the incident wave in the MPP holes: predicted from Eq. (15) (solid gray); from Kundt’s tube measurements and Eq. (15) (circles); from LSV mobility and acoustic transfer function measurements (dashed).
Simulation results on the influence of the perforation ratio on the sound absorption coefficient of a rigid (gray) or flexible (black) MPP absorber: (solid); (dashed); (dash-dotted).
Influence of the normalized perforation ratio on the first PC-controlled (solid) and HC-controlled (dashed) resonant frequencies of a thin MPPA: coupled mode analysis (gray) and vibro-acoustic model (black). Thin reference curves: HC resonance (dashed); first PC resonance (solid); and first panel resonance (dash-dotted). Upper (squares) and lower (circles) measured resonance frequencies.
Experimental results on the influence of the cavity depth on the sound absorption coefficient of a flexible MPPA (): (crosses); (circles); (dotted); (dash-dotted); (solid); (gray).
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