A type of microphone that detects sound pressure level (SPL) changes at a boundary of the acoustic space in order to reduce interference between direct and reflected sound. In a boundary microphone, the capsule is fitted flush in a surface that is large and flat compared to the wavelength of sound being captured. This produces a semi-omni-directional pick-up pattern. Boundary Microphone is also referred to as Pressure Zone Microphone (see WFTD PZM).

