The technology described in this document can be embodied in an apparatus that includes an array of multiple microphones, and a passive directional acoustic element disposed between at least two of the multiple microphones. The passive directional acoustic element includes a pipe having an elongated opening along at least a portion of the length of the pipe, and an acoustically resistive material covering at least a portion of the elongated opening. One or more structural characteristics of the passive acoustic element is configured for capturing a target frequency range in accordance with a target beam pattern associated with the array.