求翻译：The earplugs were actually sonic filter sponges, cannibalized from fairy Lower Elements Police helmets. Butler had obtained the helmets, along with a treasure trove of fairy technology, over a year previously when one of Artemis’s schemes pitted him against a fairy SWAT team. The sponges were grown in LEP labs, and had tiny porous membranes that sealed automatically when decibel levels surpassed safety standards.是什么意思？

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