An acoustic device (100) comprises an array of acoustic membranes (1,2,3,4) formed on a foil (10). Each of the acoustic membranes (1,2,3,4) is configured to vibrate at a resonance frequency (Fr) of the acoustic membranes (1,2,3,4) for generating respective acoustic waves (W1,W2,W3,W4). Relative phases (ΔΦ12,ΔΦ34) are determined at which the acoustic membranes (1,2,4,5) are actuated for generating a predetermined interference pattern (C) between the acoustic waves (W1,W2,W3,W4). A lamb wavelength (λs) is determined of lamb waves (Ws) at the resonance frequency (Fr) traveling through intermediate sections (10i,10j) of the foil (10) between adjacent acoustic membranes (1,2; 3,4). Distances (X12,X34) of the intermediate sections (10i,10j) between the adjacent acoustic membranes (1,2; 3,4) in the layout are determined in accordance with the relative phases (ΔΦ12,ΔΦ34) and the lamb wavelength (λs) for having the lamb waves (Ws), generated by one acoustic membrane (1,3), arrive in phase with an adjacent acoustic membrane (2,4).