# Experimental/Numerical Acoustic Assessment of Aircraft Beat Headsets Based on Electrospupn Mats
## 4 Results and Discussion  
Charts of Sound Pressure Level as a function of frequency for the different configurations of headrest and source location are shown in Figure 11 for the experimental tests, and in Figure 12 for the numerical ones.  
Based on the analysis of the results of Figure 11, the following comments can be highlighted:  
Figure 10: Absorbing coefficients for PVP nanofiber textile and the reference material.  
Figure 9: (**a**) BEM models; (**b**) close up of the model for the folded headrest and the monopole source positioned at 0\({}^{\circ}\).  
* There are some improvements provided by the PVP nanofiber insertions for almost all the configurations in the range 800-1400 Hz, whereas no differences are observed when the monopole source is positioned at 90 deg.
* No significant effect of modifications of both headrest geometry and cover textile is noticeable below 600 Hz. This can be attributed to the fact that at such low frequencies the acoustic wavelengths are larger than the largest headrest size; therefore, no significant alterations in the sound field can be achieved by modifying the headrest shape.
* Benefits of the different textiles and shapes on the SPL are lower when increasing the distance between the source and the headrest. Less benefits can be therefore expected when the acoustic sources are far from the headrest.  
Figure 11: Cont.  
For a fair comparison of the presented numerical and experimental analyses, some elements of approximation should be taken into consideration. The nanofiber insertion impedances adopted in the simulation were measured for a textile thickness equal to nearly 1 cm, slightly different from the one adopted experimentally, close to 1.5 cm. Moreover, numerical simulations assumed the material's impedance as independent from the angle of incidence and equal to the value obtained by experimental characterization with the [PERSON]'s tube [17; 18; 19]. Thereby, it was assumed a perfectly normal incidence of the sound waves, whereas in the studied scenario--as in most of the real-life conditions--acoustic excitations with a different angle of incidence are occurring. Despite these elements of approximations, the accordance between numerical and experimental trends was judged as acceptable.  
All of the \"unfolded\" headrest configurations outperform the \"folded\" ones throughout the considered frequency range. Moreover, as also confirmed experimentally (Figure 11), significant attenuations were achieved in the range of 600-1400 Hz by the adoption of the PVP nanofiber insertions.  
Figure 11: Experimental results in terms of SPL vs. frequency spectra for different headrest’s configurations; monopole source at a distance equal to (**a**) 75 cm or (**b**) 150 cm; “PVP” or “Base” refer to the configurations with or without the PVP + silica nanofibrous insertions in the caps.  
The highest acoustic load for an aircraft cabin during the cruise is the one generated by the external TBL, reaching a peak value at a frequency of nearly 1 kHz [23]. Hence, the adoption of these PVP insertions can also lead to some advantages in this critical low frequency range. Finally, further experimental and numerical investigations are also currently under development for frequencies higher than 1600 Hz.