Acoustic metamaterials hold great potential for applications in the sensing and control of sound waves. These materials rely on their geometry, not their composition, for functionality, but their geometric configurations are usually fixed when they are fabricated, limiting their potential. In this study, researchers exploit the reversibility, reprogrammability, and inherently nondestructive nature of nonlinear magnetic lattices to engineer the propagation of sound waves through two distinct configurations (phases) of a metamaterial. Harnessing the unique wave-control properties of each phase yields a robust wave filter for ultralow-frequency sound waves that is $t\phantom{\rule{0}{0ex}}u\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}b\phantom{\rule{0}{0ex}}l\phantom{\rule{0}{0ex}}e$ in real time.