# A Wearable Microphone Array Helmet for Automotive Applications  
[PERSON]  
1 Department of Engineering for Industrial Systems and Technologies, University of Parma, 43124 Parma, Italy; [EMAIL_ADDRESS] (D.P. ); [EMAIL_ADDRESS] (M.B. ); [EMAIL_ADDRESS] (A.F.) [PERSON]  
2 Department of Engineering and Architecture, University of Parma, 43124 Parma, Italy 22 Centro de Investigacion de Investigacdetect pedestrians in an autonomous emergency braking system. Finally, [PERSON] et al. attempted to enhance hands-free communication by integrating a microphone array into the seat belt [7]. The usage of microphone arrays for hands-free communication inside cars is widely studied and offers a large volume of the literature, among which three relevant references worth to be cited are [8; 9; 10]. Active Noise Control (ANC) is another field where microphone arrays find relevant practical applications in the automotive industry. In [11], linear and circular arrays with 4, 8, 16, or 32 capsules were employed to enhance noise cancelling inside a car cabin by means of the virtual sensing technique. A comprehensive review of virtual sensing algorithms for ANC can be found in [12]. In [13], a head-shaped array with 32 capsules and 8 cameras was used to spatially assess the effectiveness of an ANC system installed in a segment-D car. In [14], two linear arrays of 6 microphones were each used to enhance the performance of an ANC system by means of the noise source separation technique. From the previous examples, it is evident that geometry plays a crucial role when designing a microphone array. In fact, it determines the portion of space where the system exhibits optimal accuracy, such as a line, a plane, a half-space, or the full sphere. As a result, microphone arrays with a variety of shapes were observed. In [15], [PERSON] et al. discussed the optimal design for linear arrays, while in [16] [PERSON] et al. did the same for planar arrays and in [17] [PERSON] et al. for the cylindrical ones. Nevertheless, most of the microphone arrays are spherical, namely the spherical microphone array (SMA), constituted by a rigid shell; however, in some applications, open frame SMA are also employed. An in-depth analysis of the design of open frame SMA is discussed in [18; 19], while four of the most relevant papers discussing design, analysis, and processing of rigid SMA are [20; 21; 22; 23]. The dimension of the array is another key factor for the design, since the larger the array, the lower the minimum frequency where beamforming is effective [24]. Therefore, large arrays, either real or virtual [25], are required to localize noise sources at low frequency. This is particularly important when dealing with ANC systems for cars, which are mostly effective at very low frequencies, e.g., 50 Hz-400 Hz for road noise as referred in [26] and up to 1 kHz for total applications such as engine noise order cancelling, as referred in [27]. Another fundamental feature for microphone array design is the number of capsules, as the closer the microphones, the higher the maximum beamforming frequency, as demonstrated in [28] by [PERSON]. Consequently, a trend toward the continuous appearance on the market of systems with an ever-increasing number of capsules was observed. The first microphone array was launched in 1978 by [PERSON] with the name \"Soundfield\" [29; 30]. It featured four capsules positioned in the vertices of a tetrahedron; several other microphone arrays featuring four capsules have come to the market in the following decades, the last of them being the Saramonic Sr-VR in 2024. In 2009, Eingemike32 (also employed in this work) was launched by [PERSON] [31], i.e., a SMA featuring 32 capsules; in 2017, the Octomic by Core Sound, featuring 8 capsules and the Zylia, another SMA featuring 19 MEMS capsules, were launched; and finally in 2023, the new Eingemike64, featuring 64 capsules was launched. In 2015, a prototype featuring 252 capsules was presented by [PERSON] et al. [32], while in 2021, [PERSON] et al.