This paper investigates the performance limitations of conventional linearly constrained minimum variance (LCMV) beamformers implemented with circular microphone arrays. In particular, we show that imposing null constraints on interference directions can lead to a deviation of the mainlobe from the desired steering angle. A theoretical analysis is presented to characterize this deviation, and a closed-form expression for the deviation is derived to reveal the underlying low-frequency behavior of LCMV beamformers. To address this issue, we propose a mainlobe-controlled LCMV (MC-LCMV) beamformer. Simulation results demonstrate that the proposed method substantially improves spatial directivity and speech enhancement performance compared with conventional LCMV beamformers.

Differential microphone arrays (DMAs) have garnered significant attention in recent research and development due to their high directivity and frequency-invariant beampatterns. However, DMAs frequently encounter substantial white noise amplification, which limits their practical applications. This paper addresses this issue by introducing a general method for designing robust DMAs with microphone arrays of arbitrary planar topology. The proposed approach approximates the beampattern using the Jacobi-Anger series expansion and constrains the white noise gain (WNG) to a specified value. This minimizes the error between the beampattern and the ideal directivity pattern while ensuring a reasonable level of robustness. A closed-form solution for the robust differential beamformer filter is derived using the quadratic eigenvalue problem (QEP) method. Simulation results demonstrate the feasibility and effectiveness of the proposed approach.

Differential microphone arrays are widely used for far-field sound acquisition due to their high directivity and compact geometry. However, they lack the flexibility to adapt in dynamic acoustic environments with multiple or moving interferers. This paper proposes a novel method for fusing multiple differential beamformers to improve robustness under such conditions. A set of beamformers is designed with distortionless constraints in the target direction and nulls in various potential interference directions. An online fusion strategy is then applied, where a subset of beamformer outputs is selected and adaptively combined at each time frame based on the criterion of minimizing the instantaneous output variance. Simulation results demonstrate that the proposed method achieves superior interference suppression and speech quality, while maintaining low computational complexity suitable for real-time processing.

Thanks to their high directivity, compact size, and reliable performance, differential microphone arrays (DMAs) have attracted great interest from both industry and academia as they have demonstrated great potential to be used in a wide range of applications for high-fidelity speech acquisition. Nevertheless, in many real-world applications, DMAs powered with fixed differential beamformers are often inadequate in suppressing interference, particularly in environments with multiple or moving sources. To address this issue, this work develops an adaptive convex combination (ACC)-based method, which combines multiple differential beamformers in an online manner for enhanced performance. While the major contribution is a new real-time processing algorithm that facilitates optimal linear combinations of different differential beamformers, making them adapted to dynamic environments, the presented method also provides valuable insights as how to combine different beamformers for online robust implementation.

This paper investigates the problem of designing differential beam-formers with planar microphone arrays to achieve not only the desired target directivity pattern but also control the beamwidth (BW) or sidelobe level (SLL). We first discuss the target directivity patterns and express the Dolph-Chebyshev polynomial based form of target directivity patterns into linear combination of cylindrical harmonics. We then address the problem of designing differential beamformers through beampattern approximation based on the Jacobi-Anger series expansion. Two methods are subsequently developed: the first one involves designing beamformers to achieve the target directivity pattern while minimizing SLL under a pre-specified value of BW and the second one aims to attain the target directivity pattern while minimizing the null-to-null BW under a pre-specified level of SLL. Simulations are carried out to validate the method and the results demonstrate the properties of the proposed method.

Differential microphone arrays (DMAs) can measure both the acoustic pressure field and the differential acoustic pressure fields, which gives them great advantages in a wide range of applications for acoustic and speech signal acquisition. The core component of DMAs is the so-called differential beamformer, the design of which typically involves taking into account the a priori knowledge about the array geometry and the desired directivity pattern that is related to the differential sound field to respond. This paper deals with the design of differential beamformers with spherical microphone arrays. It presents a novel design approach based on the null constraints formed from the desired directivity pattern. In comparison with the exiting methods, the proposed approach only requires the information of the zeros in the beampattern, which provides notable flexibility and convenience for spherical DMA design in practical applications.

Linear differential microphone arrays (LDMAs) are commonly integrated into thin and portable devices to achieve high-fidelity speech acquisition. Traditional LDMAs typically consist of only omnidirectional microphones, which impose limitations on their ability to produce steerable spatial responses due to constraints in array element directivity and linear array geometry. A recent solution to this limitation involves integrating both omnidirectional and bidirectional microphones in LDMA design, enabling the creation of steerable spatial responses. This paper extends the core idea of integrating omnidirectional and bidirectional microphones, and develops a more general and comprehensive theory and method for designing steerable LDMAs. It makes two main contributions. Firstly, it introduces a general approach to designing steerable LDMAs, in which any type of directional microphones can be used. Secondly, it gives the minimum number of omnidirectional and directional microphones required to achieve a specific order of steerable LDMA. Simulations validate the proposed method and illustrate how omnidirectional and directional sensors can be combined to form the desired LDMAs.

This paper studies the design of maximum directivity factor (MDF) beamformers based on uniform linear arrays (ULAs) consisting of acoustic vector sensors (AVSs). We first derive the main lobe constraints, which ensure that the beamformer's beampattern achieves a maximum in the look direction, and prove that any beamformer that satisfies the proposed constraints can be written as the sum of two orthogonal beamformers: the maximum white noise gain (MWNG) beamformer and a reduced-rank beamformer. Then, we derive the MDF beamformer by maximizing the directivity factor (DF) under the deduced constraints. We also derive a robust version of the MDF beamformer, which can keep the WNG above a pre-specified level. Compared to the conventional MDF beamformer based on ULAs with omnidirectional microphones, the designed MDF beamformer with uniform linear AVS arrays (ULAVSAs) can steer the beampattern to any look direction in the 3-dimensional space and achieves a higher directivity. The proposed MDF beamformer also outperforms the two-step MDF beamformer with ULAVSAs since it maximizes the DF. The proposed methods are validated through simulations as well as real experiments.

This paper is dedicated to the design of fully steerable linear differential microphone arrays (LDMAs). We analyze the steerable ideal spatial responses and explain why conventional LDMAs consisting of only omnidirectional microphones have limited steering ability. In order to circumvent this limitation, we suggest to use both omnidirectional and bidirectional (with a dipole shaped directivity pattern) microphones. We discuss the minimum numbers of omnidirectional and bidirectional sensors required for achieving steerable spatial responses and present a method to design fully steerable differential beamformers with LDMAs through the Jacobi-Anger series expansion. Simulations validate the presented technique and the steering flexibility of the designed LDMAs.