## 2 Method
### Objective Measurements
#### 2.1.2 Hall Acoustic Conditions and Measurements  
Six hall configurations have been considered in this study by varying the location of the diffusive surfaces over the lateral walls within two different main acoustic conditions of the overall surfaces of the hall: absorptive (-A) and reflective (-R) (Figure 1). Three conditions of the diffusive surfaces (Figures 1 and 2) have been tested by shifting their location over the front, mid, and rear part of each lateral wall (hereafter labeled Df, Dm, Dr, respectively). Moreover, two reference conditions, that is, all variable surfaces set in the absorptive (All-A) and reflective (All-R) mode have been considered in order to investigate the overall absolute effect of the presence of a diffusive surface. The absorptive condition was chosen for the eye-level fixed panels in all the measurements in order to avoid the strong reflections from the lower parts of the walls. The ceiling was set at the maximum operative height of 10 m, i.e., leading to a room volume of 3720 m\({}^{3}\). ISO 3382-1 [17] objective parameters have been measured in the unoccupied room conditions. A detailed description of the measurement set-up is given in [7], while here a brief overview is given in order to help the reader understand the main elements. Measurements have been carried out using the ITA-Toolbox, an open-source toolbox for Matlab [29]. Monaural and binaural measurements have been performed with twenty-four omnidirectional microphones (Sennheiser KE-4) and two artificial heads (ITA Head), respectively (Figure 2). The microphones have been set at a height of 3.7 m in a crossed array \begin{table}
\begin{tabular}{c c} \hline \hline
**Characteristic** & **Details** \\ \hline Use & Multipurpose \\ Plan type & Shoebox \\ Dimensions & H\({}_{\text{variable: H}}\)\({}_{\text{min}}\) = 3.5 m; H\({}_{\text{max}}\) = 10 m; W = 15.5 m; L = 24.0 m \\ Volume & V\({}_{\text{min}}\) = 818.4 m\({}^{3}\); V\({}_{\text{max}}\) = 3720 m\({}^{3}\) \\ Seats & Variable: N\({}_{\text{max}}\) = 350 \\ Ceiling & Variable panels: N\({}_{\text{vp}}\) = 54 \\ Long lateral walls & Variable panels: N\({}_{\text{vp}}\) = 49; Fixed panels: N\({}_{\text{fp}}\) = 12 \\ Short front/rear walls & Variable panels: N\({}_{\text{vp}}\) = 42; Fixed panels: N\({}_{\text{fp}}\) = 12 \\ Reverberation time (500–1000 Hz) & \(T_{60,\text{min}}\) = 0.4 s; \(T_{60,\text{max}}\) = 4 s \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Architectural and acoustical details of the ESPRO based on [PERSON] [27; 28]. Figure 1: Surface acoustic conditions absorptive, reflective, and diffusive (A, R, and D). Interior view and simplified models of the eight configurations of the hall. Six configurations tested with three different locations of the diffusive surfaces (Df-A, Dm-A, Dr-A, Df-R, Dm-R, Dr-R) and two reference conditions (All-A and All-R). that extended to one of the two halves of the audience area (Figures 1 and 2). This height was chosen in order to reach the center of the first level of variable panels. Additionally, the artificial heads (Head 1 and Head 2) have been placed in the middle of the microphone array in order to be representative of the largest number of receiver positions and adjusted at an ear height of 3.7 m from the floor level as the omnidirectional microphones. Head 1 was located close to the central symmetry axis of the room and Head 2 at the midway between the axis and the lateral wall. The impulse responses at these positions have been used for the auralization introduced in the listening test session. Two omnidirectional sound sources have been positioned at the front part of the room. Each source consisted of a three-way system of low, medium, and high-frequency sources, which were positioned at different heights, that is, at 0.40, 3.70, and 3.90 m, respectively [7]. The excitation signal was an exponential sine sweep with a sampling rate of 44.1 kHz, a length of 16.8 s, and a frequency range separated for each speaker of the sources.