## 2 Materials and Methods
### Calibration  
The calibration procedure of the sound reproduction systems used for the listening part of the experiment consisted of several steps. Firstly, the reproduction level of the pair of loudspeakers was calibrated at 80 dBA using broadband pink noise limited to the common frequency range of speech, i.e., from 50 to 5000 Hz. The bandwidth of the pink noise was limited to 5 kHz to avoid coloration of the reproduced pink noise at high frequencies that could possibly influence the subjective calibration process, although it was performed only informally. The coloration stems from the comb filtering effect that appears at high frequencies due to the proximity of the table surface to both the loudspeaker and the listener, but also due to the diffraction from the edges of the computer monitor that was placed on that table. Moreover, the broadband A-weighted levels of full-band and filtered pink noise differ by less than 0.5 dB, thus, the required calibration level is maintained. The reproduction level was measured at the position of the listener, i.e., their head, using a class-1 sound level meter. After this, a dummy head was placed at the same position. Pink noise was reproduced over loudspeakers once again and was recorded using the dummy head and REAPER v6.45, developed by COCKOS Inc. from Rosendale, NY, USA as the DAW software of choice After that, the chosen pair of headphones was placed on the dummy head. Pink noise was reproduced over them and recorded the same way as before. To equalize the loudness of the two recordings, i.e., the sounds heard by the dummy head, a feature of the DAW software was used, regarding the analysis of loudness of recordings. In particular, the loudness of the two recordings was analyzed in terms of the so-called Loudness Units Full Scale (LUFS), and the headphone output level was adjusted so that the obtained LUFS values were equal for both recordings [36].  
As an informal test, a similar, but purely subjective loudness-matching calibration procedure was conducted using a small group of expert listeners. They were asked to listen to the same pink noise while alternating the reproduction between loudspeakers and headphones, and to adjust the headphone level until the perceived loudness of pink noise was the same on both systems. For every listener, the set headphone level differed from the one obtained as described above by no more than 1.5 dB. This result suggests that even a purely subjective loudness-matching level calibration of the two systems would work reasonably well.  
The calibration procedure for the reading part of the experiment consisted of recording the pure 1-kHz tone of a class-1 calibrator with the known level of 94 dB placed onto the microphone. All recordings of read speech that were made during the experiment were analyzed and their level was referenced to the known level of the recorded calibrator signal. As the experiment was conducted over several days, the calibration tone was recorded each day before starting the recording test session and also at the end of the day. The analysis of the calibration recordings reveals that the gain structure in the recording system remained stable and practically unchanged over the course of the experiment, i.e., the observed changes were lower than 0.1 dB.