# Open-Plan Offices: Comparison of Methods for Measuring Psychoacoustic Intelligibility Parameters
## 3 Results
### Acoustic Analysis of Intelligibility
#### 3.2.1 Analysis by Objective Methods  
For the acoustic analysis with objective methods, the Dirac\({}^{\circledR}\) software was used with reverberation and speech parameters according to ISO 3382, from which some were selected for analysis. The reverberation parameters used were early and late sound energy ratio with sound decay measurements below \(-\)60 dB because sound behavior in offices is generally explained by early energy. The reverberation parameters used in this study were the Early Decay Time (_EDT_), which is based on the first and earliest reflections for a sound decay of \(-\)10 dB. Other parameters used were reverberation time (_RT_), for a sound decay of \(-\)60 dB and T30, for a sound decay of \(-\)30 dB, the latter being recommended for offices. According to ISO 3382, the speech parameters used for analysis were Speech Transmission Index (_STI_) and Loss of Articulation of Consonants (_%ALCons_). The _%ALCons_ was a parameter used to represent the subjective methods apart from the subjective rating categories, which are also provided by the Dirac\({}^{\circledR}\) software. After the experimental design, 408 data were obtained for each parameter (_EDT_, _RT_, _T30_, _STI_, and _%ALCons_) with all combinations of the factors of interest. A GLM analysis was performed to explain the behavior of the data. Reverberation parameters did not present significant changes with the factors of interest of the study. Only three measurement points presented changes in the average measured time:  
* Point 8, when office noise was emitted from sources located outside the work area with a medium effect, the _EDT_ averaging time decreased (\(\beta=-1\mathrm{E}^{-6}\), d = 0.63). This point is in an area with _SPL_ changes and near the glass walls, which causes sound reflection. * Point 15, the _EDT_ varied when the office noise was emitted, but depending on the location of the external sound source was the contribution to the average time. This means that when the emission came from the position to the right near the wall (L1A), there was a small effect in the decrease in the _EDT_ (\(\beta=-1\mathrm{E}^{-6}\), d = 0.20). On the other hand, if the emission came from the position to the center of the window (L1B) with a large effect, the _EDT_ times increased (\(\beta=2\mathrm{E}^{-5}\), d = 1). This point is in a zone without _SPL_ changes and close to an open space. * Point 16, the _EDT_ presented changes in the meantime when no sound was emitted from the external sound source positioned at the center of the window (L1B). This decreased the _EDT_ (\(\beta=-1\mathrm{E}^{-6}\), d = 1). This point was located close to glass walls but abutted the unfurnsibed open space. Figure 3: Scheme of the sound factors of the study. This schematic represents the sound heat map, with a color scale for the position of each measurement point within the working area. On the other hand, intelligibility parameters presented significant changes with respect to some factors. The speech transmission analysis showed that STI changed its value with a small effect when assigning measurement point (\(p\) = 0.009, f = 0.33) and with the location of the sound source (\(p\) < 0.001, f = 0.28), while STI changed with a large effect when varying the type of sound (\(p\) < 0.001, f = 0.55) (Figure 4). During the study, the mean value of the intelligibility levels was \(STI\) = 0.68, indicating a good overall speech quality level for the room. In addition, the \(STI\) presented specific significant changes (Figure 5).