A microphone assembly includes a substrate, an acoustic transducer, an integrated circuit, and a cover couples to the substrate to enclose a back volume of the microphone assembly in which the acoustic transducer and the integrated circuit are disposed. The acoustic transducer includes a back plate and a diaphragm oriented parallel to the back plate disposed over an aperture in the substrate to receive acoustic signals. The cover is a metallic material with a thickness and a corresponding thermal diffusivity to attenuate incoming radio-frequency signals. The attenuation of the radio-frequency signals prevents ambient noise detectable by the microphone assembly.