## 1 Introduction  
Nowadays, due to technological progress, noise level enhancement has been observed. Machines and devices commonly used in industry and everyday life generate noise, which may cause health damage. Noise is also one of the factors influencing mental performance [1]. Therefore, high efforts are made to reduce the noise pollution in the human environment. In general, noise can be divided into high-, mid- and low-frequency noise. Low-frequency noise, considered in the frequency range up to approximately 500 Hz, is most difficult to limit due to passive barriers' inefficiency at this frequency range (when the noise frequency decreases, the mass, dimensions and cost of passive elements generally increases in order to be effective [2]). As an alternative or complementing solution, active control methods can be employed [3; 4; 5; 6]. They can be used, e.g., to reduce noise entering through open windows [7; 8]. Active methods are especially efficient at the low-frequency range, where passive barriers are infeasible [9]. However, when classically employed, they practically result in generating local zones of quiet, whereas at other areas the noise is reinforced. This requires additional care if the users are moving or the noise is nonstationary. Additionally, the number of secondary sound sources needed to make the zones controlled is high, which increases the total cost and highly interferes with the environment, making the solution unacceptable for many applications. In this research, an active noise-reducing casing is investigated. The active casing encloses a device that generates an excessive noise. The original device casing may be used if it is made of thin walls or the device can be surrounded by an additional casing satisfying such requirement. The control system of the casing operates according to the Active Structural Acoustic Control (ASAC) approach. This means that by actively controlling vibrations of the casing panels, the noise emission to the environment is reduced. The ASAC approach represents several advantages over a typical Active Noise Control (ANC), where loudspeakers are used as the secondary sources [10; 11]. The most important feature is that the active casing provides a global noise reduction in a whole room (reduces the noise emission), instead of creating only local zones of quiet and enhancing the noise elsewhere. This is a very desirable property of any active noise-reducing system. Efficiency of this method was previously investigated by the authors and the results have been reported in multiple publications [12; 13; 14]. However, in the previous research, the active casing was placed distant from the walls of the room the casing was enclosed by. In this paper, the active casing is located in a corner and such placement is intentionally used to facilitate the active control system's operation. Moreover, such placement of a device can be commonly encountered in real life. The presented research aims to evaluate the hypothesis that placing the active casing in a corner and appropriately rearranging the microphones can lead to both enhanced noise reduction levels and a wider frequency range of global noise reduction (in the entire room). A proper theoretical justification for such behavior is provided. The noise reduction performance is investigated and compared for multiple configurations, including a range of distances from the corner and different error microphone arrangement. The analysis of both primary and secondary paths is also given. Advantages and drawbacks of different active casing configurations are presented and discussed. The remainder of the paper is organized in five sections. Section 2 describes the laboratory setup, i.e., the light-weight active casing and utilized actuators and sensors. Section 3 describes research experiment assumptions. The placement of the active casing in the corner is described and error microphones arrangements are depicted.