The microphone shall be a surface mounted, aluminum, electret condenser microphone with a bi-directional polar pattern. The visible diameter and height of the microphone above the mounting surface shall be 1 1/4" (32mm) and 5/8" (24 mm). The microphone shall be resistant to RF interference from portable mobile and handheld devices. The frequency response range shall be 50 Hz to 17kHz and the sensitivity 14 mV/Pa.