Fig. 4: The meta-mufflers are constructed through the parallel arrangement of multiple Helmholtz resonators.
From: Resonance-based acoustic ventilated metamaterials for sound insulation
a The double-layer acoustic muffler and sound transmission loss spectrum. Reproduced with permission from ref. 72. b The acoustic metamaterial consists of multiple layers of monopolar point scatterers cascaded together, along with the configurations of a monopolar point scatterer and an individual resonator within it. The spectrum presents the sound absorption coefficient. Reproduced with permission from ref. 59.
