The acoustic quality of learning spaces, such as classrooms, is a worldwide issue. Some countries have regulations or guidelines for these environments, which does not happen properly in Brazil. Beyond the lack of nationwide research related to classroom acoustics, Brazil has two standards with a few information related to classroom acoustics. One of them was written in 1992, having a single demand concerning an appropriate reverberation time for conference rooms at the 500 Hz frequency, without detailed requirement, in contrast to other national guidelines. Another one, updated in 2020, recommends the sound pressure levels for indoor environments, having classrooms in its list. The aim of this study is to analyze the acoustic quality of two Brazilian classrooms over a public university in the south part of Brazil. Several impulse responses were taken within the learning environments and then processed in Matlab with the ITA ToolBox. The classrooms were also modeled into RAVEN and I-SIMPA software aiming to identify different sound absorption schemes to improve their speech intelligibility. The findings showed that the classrooms had a bad acoustic environment, with a measured reverberation time of approximately . However, the simulation suggested that implementing sound absorption strategies could reduce the reverberation effects by half, bringing it closer to optimal levels. The estimated costs for implementing sound absorbers were for Classroom 01 and for Classroom 02.
van den HeuijKGovertsTNeijenhuisK, et al. Challenging listening environments in higher education: an analysis of academic classroom acoustics. J Appl Res High Educ2021; 13(4): 1213–1226.
2.
BottalicoPAstolfiAHunterEJ.Teachers’ voicing and silence periods during continuous speech in classrooms with different reverberation times. J Acoust Soc Am2017; 141(1): EL26.
3.
MealingsK.Classroom acoustics and cognition: a review of the effects of noise and reverberation on primary school children’s attention and memory. Build Acoust2022; 29(3): 401–431.
4.
International Organization for Standardization. ISO 10534-2. Acoustics – Determination of sound absorption coefficient and impedance in impedance tubes – Part 2: Transfer-Function Method. Technical Report. International Organization for Standardization, 1998.
5.
International Organization for Standardization. ISO 354.Acoustics – Measurement of sound absorption in a reverberation room. Technical Report. International Organization for Standardization, 2003.
6.
AmlaniAMRussoTA.Negative effect of acoustic panels on listening effort in a classroom environment. J Am Acad Audiol2016; 27(10): 805–815.
7.
LabiaLShtrepiLAstolfiA.Improved room acoustics quality in meeting rooms: investigation on the optimal configurations of sound-absorptive and sound-diffusive panels. Acoustics2020; 2(3): 451–473.
8.
RussoDRuggieroA.Choice of the optimal acoustic design of a school classroom and experimental verification. Appl Acoust2019; 146: 280–287.
9.
AstolfiAMinelliGPuglisiGE.A basic protocol for the acoustic characterization of small and medium-sized classrooms. J Acoust Soc Am2022; 152(3): 1646–1659.
International Organization for Standardization. ISO 3382-1. Acoustics – Measurement of room acoustic parameters – Part 1: Performance spaces. Technical Report. International Organization for Standardization, 2009.
12.
BistafaSR. Acústica aplicada ao controle do ruído, São Paulo, Brazil, 2018.
13.
MinelliGPuglisiGEAstolfiA.Acoustical parameters for learning in classroom: a review. Build Environ2022; 208: 108582.
14.
Van ReenenCManleyD. Classroom acoustics: Mainstreaming and application of standards. Proc Mtgs Acoust2023; 51(1): 015003.
15.
Brazilian Association of Technical Standards. NBR 12179. Acoustic treatment in closed rooms – Procedure. Technical Report. Brazilian Association of Technical Standards, 1992.
16.
Brazilian Association of Technical Standards. NBR 10152. Acoustics – Sound pressure levels of indoor environments. Technical Report. Brazilian Association of Technical Standards, 2020.
17.
Brazilian Association of Technical Standards. NBR 10151. Acoustics – Measurement and evaluation of sound pressure levels in inhabited environments – Application for general use. Technical Report. Brazilian Association of Technical Standards, 2019.
18.
BadinoEShtrepiLAstolfiA.Acoustic performance-based design: a brief overview of the opportunities and limits in current practice. Acoustics2020; 2(2): 246–278.
19.
VorländerM.Computer simulations in room acoustics: concepts and uncertainties. J Acoust Soc Am2013; 133(3): 1203–1213.
20.
Deutsches Institut für Normung. DIN 18041. Acoustics quality in rooms – Specification and instructions for the room acoustics design. Technical Report. Deutsches Institut für Normung, Berlin, 2016.
21.
Ente Italiano di Normazione. UNI 11532-2. Caratteristiche acustiche interne di ambienti confinati – Metodi di progettazione e tecniche di valutazione – Parte 2: Settore scolastico. Technical Report. Ente Italiano di Normazione, 2020.
22.
MartellottaFD’albaMDella CrociataS.Laboratory measurement of sound absorption of occupied pews and standing audiences. Appl Acoust2011; 72(6): 341–349.
KleinerMTichyJ.Acoustics of small rooms. London: CRC Press, 2014.
25.
VorländerM.Auralization: fundamentals of acoustics, modelling, simulation, algorithms and acoustic virtual reality. RWTHedition. Aachen, Germany: Springer International Publishing, 2020.
26.
CoxTd’AntonioP.Acoustic absorbers and diffusers: theory, design and application. Boca Raton, FL: CRC Press, 2016.
27.
BrandãoESantosESMeloVS, et al. On the performance investigation of distinct algorithms for room acoustics simulation. Appl Acoust2022; 187: 108484.
28.
TorresJCBAspöckLVorländerM.Comparative study of two geometrical acoustic simulation models. J Braz Soc Mech Sci Eng2018; 40(6): 300.
29.
SchröderDVorländerM.RAVEN: a real-time framework for the auralization of interactive virtual environments. In: Proceedings of the forum acusticum, Aalborg, Denmark, 2011, pp.1541–1546. Aalborg, Denmark: European Acoustics Association.
30.
PelzerSAspöckLSchröderD, et al. Integrating real-time room acoustics simulation into a CAD modeling software to enhance the architectural design process. Buildings2014; 4(2): 113–138.
31.
BrinkmannFAspöckLAckermannD, et al. A round robin on room acoustical simulation and auralization. J Acoust Soc Am2019; 145(4): 2746–2760.
32.
PicautJFortinN.SPPS, a particle-tracing numerical code for indoor and outdoor sound propagation prediction. In: d’AcoustiqueSF (ed.) Acoustics 2012. Nantes, France, 2012. https://hal.archives-ouvertes.fr/hal-00810894 (accessed 10 August 2023).
33.
NussbaumerPPicautJ.Analyse et choix des paramètres d’entrée d’un modèle de lancer de particules dans le cas de réflexions spéculaires en acoustique des salles. In: Congrès Français d’Acoustique 2014. Poitiers, France, 2014, P.7p. https://hal.archives-ouvertes.fr/hal-01069841 (accessed 8 July 2023).
NowoświatA.Impact of temperature and relative humidity on reverberation time in a reverberation room. Buildings2022; 12(8): 1282.
36.
TronchinL.Variability of room acoustic parameters with thermo-hygrometric conditions. Appl Acoust2021; 177: 107933.
37.
BoucherMARychtarikovaMZelemL, et al. Reverberation time and audibility in phased geometrical acoustics using plane or spherical wave reflection coefficients. J Acoust Soc Am2019; 145(4): 2681–2690.
38.
International Organization for Standardization. ISO 3382-2. Acoustics – Measurement of room acoustic parameters – Part 2: Reverberation time in ordinary rooms. Technical Report. International Organization for Standardization, 2008.
39.
International Electrotechnical Commission. IEC 60268-16. Sound system equipment – Part 16: Objective rating of speech intelligibility by speech transmission index. Technical report. International Electrotechnical Commission, 2020.
40.
PierceAD.Acoustics: an introduction to its physical principles and applications. New York, NY: Springer, 2019.
41.
BerzbornMBomhardtRKleinJ, et al. The ITA-Toolbox: An open source MATLAB toolbox for acoustic measurements and signal processing. In: 43th Annual German Congress on Acoustics, Kiel, Germany, 6–9 March 2017. http://publications.rwth-aachen.de/record/687308 (accessed 10 July 2023).
42.
JamesA.Uncertainty in room acoustics measurements. In PetersR (ed.) Uncertainty in acoustics: measurements, prediction and assessment. Boca Raton, FL: CRC Press, 2021, pp. 175–217.
43.
ZhuPMoFKangJ.Influence of sound source characteristics in determining objective speech intelligibility metrics. Appl Acoust2015; 89: 188–198.
44.
Gomez-AgustinaLAygunHMohanLST. Non-special loudspeakers as speech test sources in natural acoustics speech intelligibility investigations. Acoustics2023; 5(3): 619–630.
R Core Team. R: a language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria, 2022. https://www.R-project.org/ (accessed 16 July 2023).
47.
FarinaA. Simultaneous measurement of impulse response and distortion with a swept-sine technique. In: Proceedings of the 108th Convention of the Audio Engineering Society, Paris, France, 2000.
48.
International Organization for Standardization. ISO 354. Acoustics – Measurement of sound absorption in a reverberation room. Technical Report. International Organization for Standardization, 2003.
49.
BradleyJReichRNorcrossS.A just noticeable difference in c50 for speech. Appl Acoust1999; 58(2): 99–108.
