## 1 Introduction  
An active noise control (ANC) system consists of an electroacoustic device designed to eliminate an unwanted sound by superposing a signal of equal amplitude and opposite phase, sometimes defined as an anti-noise signal, computed through an adaptive algorithm. This technology was proposed and patented by [PERSON] in 1936, but the development of ANC systems started only in the 1980s with the arrival of digital signal processors (DSPs) on the market [1]. In recent decades, ANC has attracted significant interest for applications in several fields [2, 3], where traditional solutions are not very effective due to the low-frequency range of the disturbance. Indeed, ANC is typically used to cancel noise at low frequency, where a low sampling rate makes it possible to process the measured data and generate the output signal in real time. Four main configurations of active noise control systems can be found in the literature, mainly depending on the type of source of unwanted noise and on the a priori knowledge of the kind of noise emitted [4]. In a feed-forward ANC system, a reference sensor (such as a microphone or an accelerometer) measures the signal of the annoying sound source. The implementation of this ANC configuration is convenient and widely applied whenever it is possible to sense a noise signal coherent with the source to be attenuated. Nevertheless, this is not always possible or convenient, and in such cases, a feedback configuration is preferable. This other approach does not use a reference sensor but models the reference signal from the sensing of the error signal; thus, this type of system works well for a predictable noise signal, as in the case of periodic signals. Hybrid ANC configurations combine the feed-forward approach to control broadband noise with a feedback algorithm dedicated to narrowband components [5; 6]. When the noise source signal is known a priori, ANC configurations with filter coefficients fixed in time rather than computed in real time through an adaptive algorithm can also be used [7; 8]. The performance of the ANC system strongly depends on the type of application. For example, in an enclosed space, in which the modal response of the cavity creates a complex acoustic field, the ANC systems suffer from the presence of reflections related to the cavity boundaries, generally limiting the attenuation capacity. In this case, multiple control sources and error microphones are necessary to control the noise, optimizing their position to avoid placing them in pressure nodes [4]. However, only a few applications of multichannel ANC systems in enclosures can be found in the literature. In particular, these studies are mainly related to the field of transport. For example, in the automotive industry, where research is imprinted to find light solutions to limit the increment in fuel consumption respecting the volumetric constraints, the target is to cancel the noise perceived inside the car compartment [9]. One of the typical strategies regards the implementation of the Least Mean Squares algorithm with a filtered reference signal (FXLMS) and its variations, which represents the most common choice in practical applications for its simplicity of implementation and robustness. This is usually employed for engine noise attenuation not only on cars [10; 11] but also on work vehicles such as tractors [12; 13], harvester machines [14] or loader machines [15]. Other types of noise sources, such as road noise, have a broadband nature but have some characteristics independent of the vehicle speed. In this case, also to limit stability problems, the main strategy regards the use of fixed precalculated filter coefficients [7; 16]. Some more innovative algorithms can be found in the literature [17], but they are limited to experimental tests in the laboratory. Even if these LMS-based algorithms have been widely developed in recent decades, a fair comparison among different algorithms in a multichannel configuration applied to an enclosed space is still missing in the literature.