# Open-Plan Offices: Comparison of Methods for Measuring Psychoacoustic Intelligibility Parameters
## 2 Materials and Methods  
The present study consists of comparing the methods of measuring intelligibility to evaluate the behavior of the sound conditions and the size of the effect they have on the parameters at the measured points. The study was carried out in the library of a university in northern Mexico, where the computer service area was selected. The computer service area is an open-plan office with an ABW design. The office has a space of 789 m\({}^{2}\), five private offices, a boardroom, and a data center area. In the open-plan office, there are 24 shared workstations with four cubicles per workstation. In terms of interior design features, the offices have glass walls, carpeted floors, and two wooden staircases. The rest of the space has painted cobblestone walls, two large windows, and an artificial garden with stone flooring on one side. Within the selected area were 12 workstations, for which 18 measurement points were located for the acoustic study (Figure 1). The acoustic analysis consisted of an environmental noise study and an intelligibility acoustic study. The environmental noise study was carried out according to Mexican standards using a type 2 sound level meter. In contrast, the acoustic study was performed according to ISO international standards using a microphone and two omnidirectional loudspeakers. In addition, two sound recordings were used. The environmental noise analysis was performed to identify the sound conditions of the office, and the acoustic analysis was carried out to evaluate the intelligibility in the different places of the selected area. In Mexico, there is no specific regulation on acoustics in open-plan office environments since Mexican regulations refer to the evaluation and control of noise in workplaces. The environmental noise study was carried out based on NOM-011-STPS-2001 Noise [26]. The soundscape of the office studied has stable noise. Based on NOM-011 Noise, the environmental noise study was conducted with the Sound Pressure Gradient method, for which two trajectories were established (linear and transverse), and sound pressure levels were measured with a type 2 sound level meter at different measurement points, looking for differences of 3 dB to identify changes in sound power in the area. The measurement points were assigned according to NOM-011, which requires that dimensional measurements be taken at the beginning of the study and then the space be divided into a grid. In this study, the grid was formed with 46 measurement points with 3 m. On the other hand, the acoustic analysis was performed with architectural acoustic design techniques by estimating the reverberation of the enclosure. For the analysis of intelligibility, the specialized software Dirac(r) version 6 was used. To determine the architectural acoustic design criteria, the reverberation characteristics of the enclosure were estimated. First, the  
Figure 1: Layout of the computer service area. size of the enclosure was calculated: \(P\) (m) is the perimeter, \(A\) (m\({}^{2}\)) is the total surface, and \(V\)(m\({}^{3}\)) is the volume. Then, according to the construction materials and furniture, the absorption coefficients were determined using [PERSON]'s formula to determine the reverberation time, \(RT\) (1), for which the average absorption coefficient, \(\overline{\alpha}\) (2), was calculated. With the estimated \(RT\), an acoustic survey of the area was performed. \[RT=\frac{0.161\ V}{\overline{\pi}S_{t}} \tag{1}\]  
\[\overline{\alpha}=\frac{A_{tot}}{S_{t}} \tag{2}\]  
Sound absorption is an element used for architectural acoustic design. The degree of sound absorption of materials is estimated by the absorption coefficient \(\alpha\), which is defined as the ratio between the energy absorbed by the material and the energy incident on it. It is important to consider that the \(\alpha\) values are directly related to the physical properties of the material and vary with each frequency.