Beamforming

Array aperture (physical size) determines the wavelengths that can be effectively steered and discriminated. At low frequencies (long wavelengths), the aperture must be large relative to wavelength for good directionality. At high frequencies (short wavelengths), compact arrays work. A rule of thumb: aperture should be at least 2–4 wavelengths at the frequency of interest for useful gain.

Delay-and-sum is a fixed beamformer: weights (delays and gains) are fixed based on the desired look direction. It provides constant gain in the look direction but limited sidelobe suppression. Adaptive beamformers (MVDR, LCMV) adjust weights in real time to minimize noise power while maintaining gain toward the desired direction, providing better interference rejection.

Microphone spacing should not exceed half the shortest wavelength of interest to avoid spatial aliasing. For example, at 4 kHz (wavelength ≈ 8.6 cm), spacing should be ≤4.3 cm. Closer spacing (λ/4) provides better directivity but increases computational cost and array complexity.

Yes, beamforming is widely used in underwater sonar and marine bioacoustics. The principle is identical, but acoustic wavelengths are much longer in water than in air (speed of sound ≈1500 m/s in seawater vs. 343 m/s in air), so underwater arrays are physically larger. Multi-element hydrophone arrays enable source localization, species identification, and communication in underwater environments.

In reverberant rooms, late reflections and diffuse sound arrive from many directions. Beamformers designed for direct sound cannot suppress these diffuse components because they lack directional coherence. Acoustic preprocessing (dereverberation, inverse filtering) or multi-microphone algorithms that exploit coherence differences (superdirectional arrays, speech separation) can mitigate reverberation effects.