## 2 Methodology
### Listening Test Preparation
#### 2.3.2 Acoustic Conditions and Stimuli Preparation  
As HoH listeners wearing a cochlear implant are subject to a modification of the acoustic field in which speech communication takes place, e.g., the minimization of reverberation and background noise reduction, the objective of this study was to understand the extent to which SNRs could influence speech intelligibility while a talker is wearing face masks with different properties in terms of breathability, filtration efficiency, and acoustic attenuation. To reflect realistic and ecological situations, three SNRs were defined that represent acoustic conditions from the less challenging to the most challenging, which are, +10 dB SNR, +5 dB SNR, and 0 dB SNR. A baseline to which the results could be compared was also added; therefore, a no-noise configuration corresponding to a quiet condition was tested. As far as the selection of the noise type to be added to the listening tests, typical classroom noise was used. The noise included children talking and moving in the classroom. It was  
Figure 2: Measured sound attenuation \(\Delta\)SPL in third-octave bands for Mask 1 (\(\bullet\)), Mask 2 (\(\times\)), and Mask 3 (\(\lozenge\)).  
measured in a typical Italian primary school classroom, where reverberation time was very low, and represented an ecological noisy situation that included not only energetic but also informational content, which is indeed one of the most challenging sources of masking to be faced in everyday acoustic scenarios [31; 32].  
The sentences described in Section 2.3.1 were mixed, with noise at different levels to obtain each SNR condition (i.e., 0 dB, +5 dB, and +10 dB). To account for the effect of the face mask provided on the speech produced, the sentences were recorded in the anechoic room of the Applied Acoustics Laboratory of the Politecnico di Torino using a head and torso simulator (HaTS, model 4128-C by Bruel & Kjaer), which was used as an artificial mouth that was cover by the masks themselves. A calibrated class-1 sound level meter was then placed 1 m from the mouth to acquire the speech signal filtered using the masks. According to the test length given by [PERSON] et al. [28], which corresponded to 14 sentences produced under the same acoustic condition to obtain reliable results, a first set of 14 sentences \(\times\) 4 noise conditions (i.e., no noise, +10 dB SNR, +5 dB SNR, 0 dB SNR) \(\times\) 4 mask conditions (i.e., no mask, Mask 1, Mask 2, Mask 3) was prepared.  
As the length of the tests was challenging for the participants involved, a subset of 10 sentences was extracted from the original dataset to shorten the trial and allow a higher concentration rate to be maintained for the children. A statistical analysis was conducted to compare the results, which matched between the ones obtained with the long (14 sentences \(\times\) 4 noise conditions \(\times\) 4 mask conditions = 224 sentences overall) and with the short (10 sentences \(\times\) 4 noise conditions \(\times\) 4 mask conditions = 160 sentences overall) versions of the test. For this reason, all the results were considered together. Overall, the number of sentences administrated per listener typology can be summarized as follows:  
* 5 listeners from the EG were administered with the long version test (i.e., 14 sentences) under the no noise, +10 dB SNR, +5 dB SNR, 0 dB SNR, and No Mask, Mask 1 and Mask 2 conditions;
* 9 listeners from the EG were administered with the short version test (i.e., 10 sentences) under the no noise, +10 dB SNR, +5 dB SNR, 0 dB SNR, and No Mask, Mask 1 and Mask 2 conditions;
* 6 listeners from the CG were administered with the short version test (i.e., 10 sentences) under the no noise, +10 dB SNR, +5 dB SNR, 0 dB SNR, and No Mask, Mask 1 and Mask 2 conditions.