From Stereo to Full-Sphere Ambisonics
Conventional stereo recording captures sound along a single left–right axis, which works well for music and broadcast but limits how precisely engineers can measure or reconstruct real acoustic environments. Ambisonics microphones go far beyond this, recording an entire 360 degree audio soundfield. Using spherical microphone arrays, they sample the sound pressure around a rigid sphere and convert it into higher-order ambisonics signals that describe sound coming from every direction. This enables detailed spatial audio capture, advanced beamforming, and accurate analysis of complex soundfields, from concert halls to outdoor soundscapes. The em64d Eigenmike from mh acoustics is a sixth-order ambisonics microphone array with 64 capsules on an 84 mm sphere, designed for full three-dimensional soundfield recording. It supports precise acoustic measurements and immersive audio workflows that traditional stereo systems simply cannot match, forming a foundation for applications such as virtual reality, immersive music, and scientific soundfield research.
What Makes an Optical MEMS Microphone Different?
Most modern miniature microphones rely on capacitive MEMS structures: a thin diaphragm placed a few microns from a perforated backplate. This architecture is highly scalable for consumer devices but fundamentally constrained in noise and dynamic range, typically topping out around 70 dB SNR and 130 dB SPL acoustic overload point. Optical MEMS breaks this limitation by eliminating the backplate. sensiBel’s SBM100B optical MEMS microphone uses laser interferometry inside the package: a tiny VCSEL light source, diffractive optical element, and photodetector track diaphragm motion optically rather than electrically. With up to 20 times greater membrane movement, the design achieves 80 dB SNR, a 146 dB SPL overload point, and 132 dB dynamic range, essentially matching handheld studio condenser microphones that are 50–100 times larger. Crucially, the SBM100B is a digital-output device, simplifying integration into multi-microphone arrays optimized for ambisonics recording and advanced spatial processing.
Inside the em64d Eigenmike: 64 Optical MEMS Capsules
The em64d Eigenmike is the first ambisonics recording system to integrate sensiBel’s SBM100B optical MEMS microphone across all 64 elements of its spherical array. It maintains the familiar 84 mm rigid sphere and sixth-order ambisonics capability of the previous em64 model, but radically modernizes its internal architecture. Each SBM100B capsule contributes studio-grade performance with 80 dB SNR, 146 dB SPL acoustic overload point, and a wide 20 Hz–20 kHz frequency response at a 48 kHz sampling rate. The array achieves a spatial aliasing cutoff above 12 kHz, enabling high-frequency beamforming and detailed 3D directivity control. Compared with the earlier electret condenser design, the optical MEMS upgrade adds approximately 8 dB of SNR and 16 dB of headroom, improving both quiet ambience and loud-event recording. The em64d combines this hardware with EigenStudio control software and EigenUnit VST plugins, offering a complete platform for multi-track 360 degree audio capture and post-production.
Why Optical MEMS Matters for Professional 360 Degree Audio
Higher-order ambisonics recording depends heavily on consistency between individual microphones. Small variations in magnitude or phase responses can degrade beamforming accuracy, spatial resolution, and the realism of reconstructed soundfields. Optical MEMS technology directly addresses this requirement. The SBM100B’s digital design supports tight matching across capsules, along with the manufacturing stability and repeatability associated with MEMS processes. Surface-mount assembly and reflow compatibility simplify building dense arrays such as the em64d, shortening production lead times and reducing system-level complexity. For engineers, this translates into reliable, repeatable spatial audio capture with fewer calibration headaches. The combination of high SNR, wide dynamic range, and stable performance makes the em64d particularly compelling for professional ambisonics recording in critical environments—whether capturing orchestral performances, complex urban soundscapes, or experimental immersive audio content intended for VR and AR platforms.
New Possibilities for Immersive Sound and Acoustic Research
By coupling optical MEMS microphones with a high-order ambisonics array, the em64d Eigenmike enables applications that demand both precision and immersion. Researchers can use the system for accurate acoustic measurements, mapping three-dimensional soundfields in concert venues, industrial sites, or natural habitats. Sound designers and field recordists can capture rich 360 degree audio environments—such as dense rainforests or bustling cityscapes—with enough spatial detail to recreate them convincingly in binaural or multi-speaker playback systems. The high dynamic range allows recording both delicate ambient textures and intense transient events without compromising quality. In post-production, advanced beamforming and directional analysis help isolate sources or steer virtual microphones throughout the recorded space. As optical MEMS technology matures and scales, it is poised to become a key enabler for next-generation spatial audio capture, bringing studio-grade fidelity and precise acoustic insight to compact, field-ready ambisonics microphones.
