# Open-Plan Offices: Comparison of Methods for Measuring Psychoacoustic Intelligibility Parameters
## 2 Materials and Methods
Subsequently, to compare methods for measuring intelligibility, the Dirac\({}^{\circledR}\) acoustic software is used to measure room acoustic parameters in field or laboratory applications according to ISO 3382 (room acoustics), ISO 18233 (analysis methods), and IEC 60268-16 (speech intelligibility) [27]. The acoustic analysis was performed with objective and subjective methods. The objective methods were analyzed for the effects of sound factors such as the type of sound, the location of the sound sources, and the measurement points by means of acoustic reverberation and speech transmission parameters. With the subjective methods, the speech quality assessments were analyzed in terms of psychoacoustic parameters at each of the measurement points within the workstation area. The comparison of intelligibility measurement methods was performed considering four variables at each measured point. Two variables for the objective method were the \(RT\) and \(STI\), and two variables for the subjective method were the %ALCons and the subjective speech quality rating. All variables were obtained from the Dirac\({}^{\circledR}\) software. The subjective speech quality analysis method is based on ISO 3382-3, which ranks the \(STI\) and %ALCons values on a categorical rating scale, Table 1. On the other hand, two factors of interest were used to compare the methods: the location of the measurement points, the sound sources, and the sound conditions under which the study was carried out. The assignment of the measurement points was obtained from a sample of 18 of the 46 measurement points on the grid used in the environmental noise analysis. The location of the sound sources was determined using guidelines from the ISO 3382-3 standard. This involved utilizing data obtained from the reverberation of the room and calculating the Minimum Distance (3) \(Dmin\)[18]. \[Dmin=2\sqrt{\frac{V}{cRT}} \tag{3}\] \begin{table}
\begin{tabular}{c c c} \hline
**Speech Intelligibility** & \
\begin{tabular}{c} **Speech Transmission** \\ **Index RASTI** \\ \end{tabular} &
\begin{tabular}{c} **Percentage Articulation Loss** \\ **of Consonants (\%ALCons)** \\ \end{tabular} \\ \hline Bad & 0–0.30 & 27–46.5 \\ \hline Poor & 0.30–0.45 & 12–24.2 \\ \hline Fair & 0.45–0.60 & 5.3–11.4 \\ \hline Good & 0.60–0.75 & 1.6–4.8 \\ \hline Excellent & 0.75–1 & 0–1.4 \\ \hline \end{tabular}
\end{table} 
Table 1: Relationship between \(STI\) and %ALCons and the subjective assessment of the degree of intelligibility. The following factors were used for this study: (a) location of the sound sources--Source A was located outside the work area to meet the _Dmin_ requirements with respect to the workstations, while Source B was located inside the study area with distances less than the _Dmin_ with respect to the workstations; (b) location of the measurement points within the work area; and (c) types of sounds emitted--silence, which represents the office soundscape, and a sound recording of office noise, which is a recording with real office sounds. Additionally, the treatment of the factors was a random combination of the sounds emitted from each sound source. This formed four sound conditions: emission of office noise by source A, emission of office noise by source B, emission of office noise by both sources AB, and not emitting the background noise 0, i.e., leaving the soundscape of the office. Additionally, to control the experiment, only one frequency band was used, establishing it as a block variable because this frequency is the one that provides the greatest contribution to the intelligibility of the word [1]. Finally, the data obtained from the acoustic analysis, with the experimental design, were analyzed using a General Linear Model (GLM) to determine the behavior of the statistically significant acoustic parameters. Because some parameters did not fit a normally distributed behavior, these were adjusted with the Box-Cox power transformation for normality in the residuals.