# Experimental/Numerical Acoustic Assessment of Aircraft Beat Headsets Based on Electrospupn Mats
## 2 Experimental Campaign  
The experimental campaign was conducted in a semi anechoic chamber at CIRA (Figure 1). A dummy headrest was characterized from an acoustical standpoint, in order to compare different configurations of headrest shape and fabrics. The main purpose was to understand which combination of shape and covering materials represented the best choice in terms of noise abatement for the aircraft seat's headrest. Additionally, the performances of an innovative nanofiber textile (Figure 2a) made of PVP plus silica inclusions [17; 18; 19; 20; 21; 22] were assessed. Silica inclusions were added to the PVP nanomaterial to obtain the fire-resistant characteristics of the material and comply with flyability requirements. Such nanofiber textiles have appealing acoustic properties thanks to their small fiber dimensions that give a high surface-to-volume ratio. Such  
Figure 1: Semi-anechoic chamber at CIRA: the setup consists of a dummy seat with binaural head and configurable headrest. materials were made with an electro-spinning process (Figure 2b), which allowed us to obtain fibers with diameters of a few micrometers in the form of a textile with random fiber disposition. Several layers were then superimposed as in Figure 2b to obtain the desired mass or thickness. In the current investigation, cylindrical insertions made with several layers of PVP nanofiber textiles were embedded in the caps of the dummy headrest, see Figure 3. Different configurations for the headrest were considered to evaluate the impact of the nanofiber insertions and of the headrest shape. The insertions were added by cutting out two cylindrical sections from the headrest foam and replacing them with the nanofibrous material samples, preserving the overall mass of the headrest. Two geometries of the headrest were considered, referred to as \"folded\" and \"unfolded\" geometries hereinafter (Figure 4). In addition, the configurations including the original foam are referred to as the \"baseline\", and those with nanofiber insertions as \"insertion\". Figure 3: Configurable headrest adopted for the experimental investigations. Figure 2: (**a**) Schematic view of the electrospinning process; (**b**) layers of nanofiber textile [19]. The acoustic load consists of a monopole source positioned at different locations around the seat at head height. Figure 5 shows the different monopole source positions considered during the tests. Three different angles and two different distances from the binaural head were considered for each of the four headrest setups, thus, a total of 24 experiments were carried out. The final test matrix is reported in Table 1.  
A calibrated volume velocity source (Simcenter Qsource), with emitted sound power spectrum, shown in Figure 6, was used as acoustic monopole source (Figure 7a). A periodic chirp was used as excitation signal and a binaural head (HEAD Acoustics HMS) was used to represent the passenger during the flight (Figure 7b). The frequency range of interest was set up to 1600 Hz with a resolution equal to 0.5 Hz. Four free-field microphones were positioned at ear height, whereas two microphones were already available inside the head's ears (Figure 7b). Such a redundancy enables the assessment of the sound pressure levels over a larger area and with different microphone calibrations. The choice of the free-field microphones was motivated by the rather low-frequency range of the experiments. These were \(1/2^{\prime\prime}\) 46 AE GRAS microphones, with a nominal sensitivity of 50 mV/Pa. Figure 4: Different headrest geometries considered for the experimental investigations: (**a**) unfolded and (**b**) folded. Figure 5: Monopole source positioning for the experimental measurements.