Evaluation of the Acoustic Comfort in University Classrooms, Based on the Brazilian Technical Standard NBR 10152—Use of Noise Mapping and Acoustic Barriers to Counter Noise on a University Campus

An evaluation was made of the acoustic quality of classrooms on two campuses of the Federal University of Paraná. Despite the heavy vehicle traffic flow on the streets in and around the campuses, the noise maps of the Polytechnic Center campus indicated that the noise that reaches the facades of the buildings vary from 55 to 60 dB(A), putting this campus within the limit of 60 dB(A) established by municipal law for Special Educational Zones (SEZ). In contrast, noise pollution at the Jardim Botânico campus has reached serious proportions, with noise maps indicating that its buildings are directly affected by noise levels of 65 to 70 dB(A). A simulation of the construction of two acoustic barriers showed their effectiveness in reducing noise levels to 55 and 60 dB(A). However, the downside is that acoustic barriers are expensive to build and cause visual pollution.


Introduction
According to the World Health Organization, a large part of the world's population is affected by noise pollution, which is second only to air and water pollution (WHO, 2017). Goines and Hagler (2007) call noise pollution a modern scourge. In addition to the auditory effects of noise pollution, non-auditory effects include annoyance, cognitive impairment, sleep disorders and cardiovas-more sustained and less stressful. Excessive noise and reverberation in classrooms are obstacles to learning, insofar as they degrade or inhibit speech communication (Lubman & Sutherland, 2001). This work was guided by three main objectives: 1) Analysis of the equivalent sound pressure levels (Leq) measured in the classrooms of the Polytechnic Center and Jardim Botânico campuses of the Federal University of Paraná. 2) Comparison of the measured equivalent sound pressure level (Leq) and that recommended by ABNT, the Brazilian Association of Technical Standards, NBR 101-52-Noise levels for acoustic comfort. 3) Determination of the Noise Curve (NC) of each classroom, classifying it based on its measured equivalent sound level, as well as its subjective classification. This subjective classification may describe the classroom as very quiet, quiet, moderately noisy, noisy, very noisy and extremely noisy, according to Cavanaugh et al. (2010). The calculations for noise mapping of the front façades of buildings on the two campuses are also shown.
A scenario was simulated using two acoustic barriers to reduce the sound levels on the façades of the central building of the Jardim Botânico campus, where noise pollution is more critical. Such barriers have proven to be effective in combating noise pollution. However, the main problem is that they cause visual pollution, not to mention that their construction is expensive.

Methodology
Equivalent sound pressure levels, Leq, were measured following the guidelines of the Brazilian standard NBR 10152 on noise levels for acoustic comfort. The evaluated classrooms were furnished but unoccupied, and the only people in the rooms were the operator of the sound pressure level meter and his assistant. A

Results and Discussion
This section describes the results of the measurements taken at the Polytechnic Center of the Federal University of Paraná-UFPR. Using a B&K 2270 analyzer, Leq measurements were taken in the following spaces of the Science and Technology buildings: in classrooms PG 03, PG 11, and PF 06, as well as on the first, second and ground floor of the Library, in Study Room 2.8 of the library, and in the Study Hall facing the library, as illustrated in Figure 1.  The duration of the measurement at each point was 10 minutes. Graphs were created using Brüel & Kjaer's BZ-5503 Measurement Partner Suite, and are shown in Figures 2-9. The equivalent sound pressure level, Leq, measured in classroom PG 03 was 37 dB(A). Figure 2 also illustrates the NC 30 curve. As can be seen in the graph, the NC 30 curve touches the frequency spectrum at 4000 Hz. Table 2 lists all the locations of internal measurements, the equivalent sound pressure levels and NC curve ratings, and the subjective acoustic assessment of the environment according to Cavanaugh et al. (2010).
The LAeq measured in classroom PG 11 was 44.7 dB(A), while the NC curve was 40. The curve was found to touch the spectrum at the frequency of 4000 Hz, a frequency band that presented an LZeq of 37.8 dB. In classroom PF 06, the measured Leq was 49 dB(A). This time, the NC curve that touched the frequency spectrum was NC 45, at a frequency of 500 Hz, where the LZeq was 48.9 dB.        All the spaces had Leq values within or below the recommended range except the Study Hall, whose measured Leq was 64.8 dB(A), while the recommended maximum limit is 55 dB(A) ( Table 2). The NC rating of the Study Hall was 62, thus also exceeding the limit specified by NBR 10152, which recommends up to NC 50. Lastly, the subjective classification according to Cavanaugh et al. (2010) indicated this space was extremely noisy. It should be noted that, for this analysis, the student Study Hall was considered a "circulation area," while the other spaces were considered library and Although there are several study tables, this is a circulation area because it is close to one of the main entrances to the block and is also a meeting place. It is common to see people working together, discussing ideas and talking loudly, which explains the measured Leq levels. Be that as it may, the data collected here and analyzed indicated that this space is too noisy to be used for studying. Some noise control measure would have to be implemented to meet original purpose for which it was designed. A reformulation of the layout and/or raising the awareness of its occupants is alternatives that could be implemented. Another alternative to lower the noise levels in the room would be to line its walls and ceiling with acoustic absorbing material. The NC ratings of classrooms PG 03, PG 11 and PF 06 were 30, 40, and 45, respectively, all of them below or within the recommended limit of NC45. As for the subjective evaluation, classrooms PG11 and PF 06 were classified as moderate and PG 03 as quiet.
On the ground floor, first floor, second floor and study room 2.8 of the library, the NC ratings were 31, 31, 30 and 28, respectively. As for the perception of sound, the four spaces were classified as quiet.
The measurements taken on the Jardim Botânico campus of UFPR are presented next. The spaces measured indoors on this campus were classrooms 103, 116, 117, 118 and computer lab 128. Figure 10 illustrates the location of these rooms on the campus. These rooms were chosen so that that at least one room was measured on each side of the main building, where most of the classrooms are located. The diagonal areas of the building facing Avenida Mayor Lothário Meissner were not measured because they are staff offices. Table 3 indicates the locations of indoor measurements taken on Jardim Botânico campus, along with their equivalent sound pressure levels, NC curves, and subjective assessment of acoustic quality, based on Cavanaugh et al. (2010).    Figures 11-15 illustrate the NC curves of the locations described in Table 3. The upper line that cuts through the graph in Figure 16 represents the permissible noise limit specified by Curitiba Municipal Law 10,625 for Special Educational Zones-SEZ, while the lower line corresponds to the limit for SEZ established by Brazil's NBR 10151 standard for acoustic comfort of the community. Figure 17 shows a daytime noise map of the facades of the buildings on the Polytechnic Center. On this map, note that the facades closest to the streets and avenues on and around the Polytechnic Center campus are the ones affected by high noise levels, originating from both inside and outside the campus. The predominant colors indicate noise levels of 65 -70 dB(A) and 55 -60 dB(A), while lower noise levels of 50 to 55 dB(A) predominate further inside the campus. This finding indicates that noise levels on most of the Polytechnic Center campus falls within the limits established for educational zones by the Brazilian standard that regulates Community Noise. Figure 18 depicts a noise map of the façades of the buildings on Jardim Botânico campus.
As can be seen in Figure 18, the facades of the central building of the Jardim Botânico campus are subjected to high sound levels, particularly the entire front façade, where noise levels of 65 to 70 dB(A) were recorded. High sound levels in the range of 60 to 65 dB(A) also reached the side façade of the building. This classifies the Jardim Botânico campus as noise polluted, since the sound levels reaching the façades exceed the limit for Special Educational Zones-SEZ established by Curitiba Municipal Law 10625, which is 60 dB(A). These levels also exceed the noise limit of Leq 55 dB(A) specified by the Brazilian NBR 10151 standard for quiet zones around schools and hospitals.
In an attempt to solve the problem, the placement of noise barriers along the front of the Jardim Botânico campus was simulated, as depicted in Figure 19.

Conclusion
This work involved an evaluation of the noise levels on the Polytechnic Center and Jardim Botânico campuses of the Federal University of Paraná. The findings indicate that most of the classrooms of the Polytechnic Center offer acoustic comfort, qualifying them as "quiet" according to Cavanaugh et al. (2010). The noise maps of the buildings at the Polytechnic Center indicate a predominance of noise levels of 55 to 60 dB(A), i.e., within the limit of 60 dB(A) established by Curitiba Municipal Law 10625 for Special Educational Zones-SEZ.
On the other hand, noise levels of 65 to 70 dB (A) reach the front façades of the buildings on the Jardim Botânico campus, placing it in a situation of serious noise pollution. The noise limit established by municipal law for SEZ is 60 dB(A). To reduce these levels, simulated noise barriers were placed in front of the buildings. These simulated noise barriers proved to be highly effective, reducing the noise levels depicted in Figure 20 to 55 to 60 dB(A). However, despite the effectiveness of the simulated noise barriers in reducing noise levels on the Jardim Botânico campus, the construction of such barriers would not only involve high investment costs but also cause undesirable visual pollution.