Comparison of first-order Ambisonic microphone arrays

Today, there are several first-order Ambisonic microphone arrays commercially available. These arrays are composed of 4 cardioid capsules that are arranged on the vertices of a tetrahedron. In contrast to commonly used surround recording techniques, Ambisonic microphone arrays facilitate three-dimensional sound field recording with a single compact array. This contribution compares 3 different first-order microphone arrays in a listening experiment: Oktava MK4012, Soundfield SPS200 and ST450. The comparison includes different orientations of the arrays, as well as traditional 2-channel stereo with spaced microphones and ORTF as references. All 8 recording configurations simultaneously captured 2 sound scenes. Playback employed the hemispherical loudspeaker arrangement of the IEM CUBE. 14 subjects evaluated the reproduction in terms of Localization, Spatial Depth, Envelopment, Sound Quality and Preference. In accordance to measured directivity patterns, the perceived influence of the orientation is depending on the specific microphone array. Moreover, the results indicate that Preference is largely determined by Sound Localization and Sound Quality. Finally, we propose an orientation for first-order microphone arrays that preserves the frontal localization and sound quality of stereo, and enhances the envelopment by Ambisonics at the same time.