The influence of microphone directivity on the level calibration and equalization of 3D loudspeakers setups

With increasing popularity of 3D sound formats the issue of correctly calibrating 3D loudspeaker systems arises. The typical calibration procedure involves a single-position measurement, where the elevation angle between the microphone and the different loudspeaker layers on the vertical plane is varying. Anechoic measurements of 1/2” and 1/4” microphones show that mainly the vertical angle affects the microphone directivity. Any angle other than 0° causes high-frequency attenuation, and this is mainly dependent on the microphone diameter. The result is an erroneous calculation of the level and frequency response of a loudspeaker in a listening room. In this paper, we derive a vertical angle- and microphone-diameter-dependent compensation and apply and verify it with measurements in an ITU-R BS.1116 conform listening room.