Reverberation Time In Classrooms Research Articles

Premises for Effective Teaching and Learning: State of the Art, New Outcomes and Perspectives of Classroom Acoustics

Many booklets and standards have already been published on classroom acoustics in several countries, based on studies that were completed up to ten years ago and which were mainly focused on the speech intelligibility of pupils under noisy conditions. In the last decade many studies began to consider the complex speech communication scenario in classrooms, where acoustic requirements are needed for both teachers and pupils. The voice monitoring of teachers has revealed challenging conditions for speaking because of bad acoustics, with consequences on vocal health. Research has underlined the importance of voice support from the room, which has led us to reconsider the optimal reverberation time in classrooms, whose tendency is towards higher values than those for listening. On the other hand, it has been proven that a high reverberation increases the listening effort and decreases reading abilities. Thus, the question of the optimal reverberation time for speaking and listening arises, as well as the need to optimize the design of classrooms to support the voice and control the sound tail. The perceived reverberation is closely related to the perceived acoustical quality, which is recognized as the most important environmental aspect in classrooms. Reverberation also amplifies the noise produced by pupils themselves and affects their well-being. To cope with this, a new device has been introduced to inform pupils on the need to lower their voices and respect others. A summary of the state of the art of classroom acoustics is given in this lecture, together with the new findings on the effects of bad acoustics on pupils' learning and well-being and on teachers' vocal behaviour. A new paradigm on speech communication is needed in classrooms that should involve both teaching and learning. Further work is required to investigate the factors that underpin this complex communication scenario.

Passive variable acoustic technology for classroom reverberation time: a case study

PurposeTo maximise acoustic comfort in a classroom, the acoustic conditions of the space should be variable. So, the optimal acoustic state also changes when the classroom changes from a study environment into a lecture environment. Passive Variable Acoustic Technology (PVAT) alters a room’s Reverberation Time (RT) by changing the total sound absorption in a room. The purpose of this paper is to evaluate the improvements to classroom acoustic comfort when using PVAT.Design/methodology/approachThe study is conducted in an existing tertiary classroom at Auckland University of Technology, New Zealand. The PVAT is prototyped, and the RTs are measured according to international standards before and after classroom installation. The acoustic measurement method used is a cost-effective application tool where pre- and post-conditions are of primary concern.FindingsPVAT is found to offer statistically significant improvements in RT, but the key benefits are realised in its’ ability to vary RT for different classroom situations. It is predicted that the RT recommendations for two room types outlined in the acoustic standard AS/NZS 2107:2016 are satisfied when using PVAT in a single classroom space. By optimising RT, the acoustic comfort during both study and lecture is significantly improved.Originality/valueWhen PVAT is combined with an intelligent system – Intelligent Passive Room Acoustic Technology (IPRAT) – it can detect sound waves in real time to identify the optimal RT. This paper details a pilot case study that works towards quantifying the benefits of IPRAT, by prototyping and testing the PVAT component of the system.Highlights A pilot case study outlines the development and test of a variable acoustic prototype in a tertiary classroomA method is adopted to measure acoustic conditions, using three under-researched Android applicationsThe benefits of PVAT are realised in its ability to vary RT by adjusting the prototypes’ sound absorptionBy using PVAT in a single space, the recommended RTs for two room types outlined in the acoustic standard AS/NZS 2107:2016 can be satisfiedThe improvements in acoustic comfort due to PVAT are statistically significant

A Review of the Effect of Classroom Sound-Field Amplification on Children in Primary School.

Being able to hear the teacher clearly is an important factor for children's learning. However, classrooms often have suboptimal listening conditions. Sound-field amplification systems (SFAS) can help improve classroom listening conditions by increasing the level of the teacher's speech compared to the background noise throughout the classroom. The aim of this review article was to review the effect of SFAS on children in primary school. A comprehensive search of four online databases (ERIC, PubMed, Scopus, and Web of Science) was conducted. The search terms were classroom sound-field amplification and classroom amplified distribution system. Twenty-one articles were deemed relevant for the review plus an additional six from their references. Most articles were published between 1996 and 2015. Only one article was published since 2016. A range of child populations were studied including typically developing children and children with difficulties and disabilities such as hearing loss, developmental language disorders, attention-deficit/hyperactivity disorder, emotional and behavior disorders, Down syndrome, and developmental disabilities. There were several different measures that were used to evaluate the effectiveness of SFAS including speech perception assessments, language assessments, academic and comprehension assessments, classroom observations, interviews, and questionnaires. Improvements with SFAS were found for speech perception, listening comprehension and auditory analysis, language outcomes, academic outcomes, and behavior. SFAS can benefit children's listening and learning; however, the child's background, classroom reverberation time (limit to < 1 s), and layout and type of learning activities, especially in modern classrooms, need to be taken into consideration.

Research and optimization of acoustic environment in ordinary classrooms of middle school

A good classroom acoustic environment will contribute to teachers’ health and students’ learning. Comfortable acoustic environment requires suitable reverberation time, sufficient loudness, uniform sound field distribution, high language clarity, and no acoustic defects such as echo and acoustic focusing. In this study, the optimization strategy of acoustic environment is proposed through the investigation, field testing and numerical simulation analysis of a middle school classroom in Wenzhou under different ventilation conditions. The results show: the key factors affecting the classroom acoustic environment are outdoor activity noise, corridor noise, and classroom teacher-student activity noise. Through optimization, the quality of classroom acoustic environment is improved significantly. Classroom reverberation time (intermediate frequency) decreased from 1.5s to 0.7s; ALC decreased from 9.65% to 4.75%; STI increased from 0.534 to 0.664. The research results provided reference for acoustic design of secondary school classrooms in the future.

Acoustics in South African classrooms: Regulations versus reality

This research set out to broaden the pool of evidence regarding the acoustic conditions at schools in South Africa. A review of local and international literature, standards and design guidelines shows that the ideal classroom acoustic conditions of 35 dBA ambient and 0.7 s reverberation time are required to enable a suitable environment for teaching and learning. A review of local literature revealed a very small body of knowledge regarding actual acoustic conditions and monitoring of classroom acoustics and that these cases demonstrated ambient noise levels in classrooms (whether occupied or unoccupied) to be above the recommendations of the relevant South African National Standard (SANS 10103). The limited local research promted the need for this case study. The findings of a province-wide survey of urban schools showed that traffic noise is the main source of noise disturbance in schools. A case study of five schools showed that the average outdoor noise level at schools exposed to traffic throughout the day is 63.3 dBA and the average indoor noise level at these schools when classrooms are unoccupied is approximately 58 dBA, which is significantly higher than the requirement. The reverberation time in classrooms was between 0.6 and 1.75 s. It is concluded that the current acoustic conditions in South African urban schools is poor when evaluated against the South African National Standards. However, since this is based on only five case studies, a broader study is required to understand the general conditions and establish suitable mitigation measures.

A Slight Increase in Reverberation Time in the Classroom Affects Performance and Behavioral Listening Effort.

The purpose of this study was to investigate the effect of a small change in reverberation time (from 0.57 to 0.69 s) in a classroom on children's performance and listening effort. Aiming for ecological listening conditions, the change in reverberation time was combined with the presence or absence of classroom noise. In three academic tasks, the study examined whether the effect of reverberation was modulated by the presence of noise and depended on the children's age. A total of 302 children (aged 11-13 years, grades 6-8) with normal hearing participated in the study. Three typical tasks of daily classroom activities (speech perception, sentence comprehension, and mental calculation) were administered to groups of children in two listening conditions (quiet and classroom noise). The experiment was conducted inside real classrooms, where reverberation time was controlled. The outcomes considered were task accuracy and response times (RTs), the latter taken as a behavioral proxy for listening effort. Participants were also assessed on reading comprehension and math fluency. To investigate the impact of noise and/or reverberation, these two scores were entered in the statistical model to control for individual child's general academic abilities. While the longer reverberation time did not significantly affect accuracy or RTs under the quiet condition, it had several effects when in combination with classroom noise, depending on the task measured. A significant drop in accuracy with a longer reverberation time emerged for the speech perception task, but only for the grade 6 children. The effect on accuracy of a longer reverberation time was nonsignificant for sentence comprehension (always at ceiling), and depended on the children's age in the mental calculation task. RTs were longer for moderate than for short reverberation times in the speech perception and sentence comprehension tasks, while there was no significant effect of the different reverberation times on RTs in the mental calculation task. The results indicate small, but statistically significant, effects of a small change in reverberation time on listening effort as well as accuracy for children aged 11 to 13 performing typical tasks of daily classroom activities. Thus, the results extend previous findings in adults to children as well. The findings also contribute to a better understanding of the practical implications and importance of optimal ranges of reverberation time in classrooms. A comparison with previous studies underscored the importance of early reflections as well as reverberation times in classrooms.

The effects of classroom reverberation time and traffic noise on English listening comprehension of Chinese university students

The importance of classroom acoustic environment to students’ listening and learning has been widely realized, especially for second-language learning classrooms. An experiment has been carried out in this paper to study the effects of classroom reverberation time (RT) and traffic noise level (TNL) on English listening comprehension (ELC) for Chinese university students. A total of 12 combination conditions of RT and TNL (3 RTs × 4 TNLs) were designed in the experiment, and their effects on both students’ objective ELC accuracy rates and subjective perception were tested. The results show TNL has significant negative impacts on students’ ELC performance (including ELC accuracy rate and subjective perception), while RT has less effect on students’ ELC performance (which has significant effects only at some particular TNL (TNL = 50 dB(A)). Based on the experimental results, an indoor TNL limitation of not >40 dB(A) is recommended for English immersion classrooms in China. In addition, students’ subjective perceptions are found to be more sensitive to the change of acoustic condition than objective performance, and subjective assessment can be considered as a more appropriate measure in classroom acoustic environment evaluation. According to the authors’ knowledge, this study is the first attempt to study the effects of classroom RT and TNL on ELC for Chinese university students. The findings can be used as a reference for the acoustic research and design of Chinese university classrooms, especially for English-teaching classrooms in China.

Feed forward neural network application for classroom reverberation time estimation

&lt;span&gt;Acoustic problem is a main issues of the existing classroom due to lack of absorption of surface material. Thus, a feed forward neural network system (FFNN) for classroom Reverberation Time (RT) estimation computation was built. This system was developed to assist the acoustic engineer and consultant to treat and reduce this matter. Data was collected and computed using ODEON12.10 ray tracing method, resulting in a total of 600 rectangular shaped classroom models that were modeled with various length, width, height, as well as different surface material types. The system is able to estimate RT for 500Hz, 1000Hz, and 2000Hz. Using the collected data, FFNN for each frequency were trained and simulated separately (as absorption coefficients are frequency dependent) in order to find the optimum solution. The final system was validated and compared with the actual measurement value from 15 different classrooms in Universiti Tun Hussein Onn Malaysia (UTHM). The developed system show positive results with average validation accuracy of 94.35%, 95.91%, and 96.42% for 500Hz, 1000Hz, and 2000Hz respectively. &lt;/span&gt;

Prediction of Classroom Reverberation Time using Neural Network

In this paper, an alternative method for predicting the reverberation time (RT) using neural network (NN) for classroom was designed and explored. Classroom models were created using Google SketchUp software. The NN applied training dataset from the classroom models with RT values that were computed from ODEON 12.10 software. The NN was conducted separately for 500Hz, 1000Hz, and 2000Hz as absorption coefficient that is one of the prominent input variable is frequency dependent. Mean squared error (MSE) and regression (R) values were obtained to examine the NN efficiency. Overall, the NN shows a good result with MSE < 0.005 and R > 0.9. The NN also managed to achieve a percentage of accuracy of 92.53% for 500Hz, 93.66% for 1000Hz, and 93.18% for 2000Hz and thus displays a good and efficient performance. Nevertheless, the optimum RT value is range between 0.75 – 0.9 seconds.

Estimation of Reverberation Time in Classrooms Using the Residual Minimization Method

Abstract The objective of the residual minimization method is to determine a coefficient correcting the Sabine’s model. The Sabine’s equation is the most commonly applied formula in the designing process of room acoustics with the use of analytical methods. The correction of this model is indispensable for its application in rooms having non-diffusive acoustic field. The authors of the present paper will be using the residual minimization method to work out a suitable correction to be applied for classrooms. For this purpose, five different poorly dampened classrooms were selected, in which the measurements of reverberation time were carried out, and for which reverberation time was calculated with the use of theoretical methods. Three of the selected classrooms had the cubic volume of 258.5 m3 and the remaining two had the cubic volume of 190.8 m3. It was sufficient to estimate the correction for the Sabine’s equation. To verify the results, three other classrooms were selected, in which also the measurements of reverberation time were carried out. The results were verified by means of real measurements of reverberation time and by means of computer simulations in the program ODEON.

Chinese speech intelligibility of children in noisy and reverberant environments

Reverberation time and signal-to-noise ratio in classrooms are critical factors to speech intelligibility. In this study, the combined effect of reverberation time and signal-to-noise ratio on Chinese speech intelligibility of children was investigated in 28 elementary school classrooms in China. The results show that Chinese speech intelligibility scores increase with an increase of signal-to-noise ratio and the age of children, and decrease with an increase of reverberation time in classrooms. Younger children require higher signal-to-noise ratio and shorter reverberation time than older children to understand the speech. The A-weighted signal-to-noise ratio combined with a wide range of reverberation time can be used to predict speech intelligibility score and serve as a criterion for classroom design for elementary schools.

Teachers' voicing and silence periods during continuous speech in classrooms with different reverberation times.

The relationship between reverberation times and the voicing and silence accumulations of continuous speech was quantified in 22 primary-school teachers. Teachers were divided into a high and a low reverberation time groups based on their classroom reverberation time (higher and lower than 0.90 s). Reverberation times higher than 0.90 s implicate higher voicing accumulations and higher accumulations of the silences typical of turn taking in dialogue. These results suggest that vocal load, which can lead to vocal fatigue, is influenced by classroom reverberation time. Therefore, it may be considered a risk factor for occupational voice users.

Aspects concerning the acoustical performance of school buildings in Portugal

Acoustic measurements were performed in eight schools of different levels of education (from kindergarten to college) located in Viseu – Portugal. The acoustic evaluation was made in order to analyze the most common problems that may condition the acoustic environment inside school building.The acoustics evaluation of school buildings was made by the measurement of: reverberation time in classrooms; sound insulation between classrooms and between classrooms and corridors; impact sound insulation of floors and airborne sound insulation of façade. The sound insulation of façade was made with all elements closed and with natural ventilation conditions (banners or windows tilt mode).It was found that most of the studied cases revealed disabled constructive aspects in relation to the acoustic requirements of school buildings compromising the quality of education.

The effects of acoustical refurbishment of classrooms on teachers' perceived noise exposure and noise-related health symptoms.

To investigate whether acoustical refurbishment of classrooms for elementary and lower secondary grade pupils affected teachers' perceived noise exposure during teaching and noise-related health symptoms. Two schools (A and B) with a total of 102 teachers were subjected to an acoustical intervention. Accordingly, 36 classrooms (20 and 16 in school A and school B, respectively) were acoustically refurbished and 31 classrooms (16 and 15 in school A and school B, respectively) were not changed. Thirteen classrooms in school A were interim "sham" refurbished. Control measurements of RT and activity sound levels were measured before and after refurbishment. Data on perceived noise exposure, disturbance attributed to different noise sources, voice symptoms, and fatigue after work were collected over a year in a total of six consecutive questionnaires. Refurbished classrooms were associated with lower perceived noise exposure and lower ratings of disturbance attributed to noise from equipment in the class compared with unrefurbished classrooms. No associations between the classroom refurbishment and health symptoms were observed. Before acoustical refurbishment, the mean classroom reverberation time was 0.68 (school A) and 0.57 (school B) and 0.55 s in sham refurbished classrooms. After refurbishment, the RT was approximately 0.4 s in both schools. Activity sound level measurements confirmed that the intervention had reduced the equivalent sound levels during lessons with circa 2 dB(A) in both schools. The acoustical refurbishment was associated with a reduction in classroom reverberation time and activity sound levels in both schools. The acoustical refurbishment was associated with a reduction in the teachers' perceived noise exposure, and reports of disturbance from equipment in the classroom decreased. There was no significant effect of the refurbishment on the teachers' voice symptoms or fatigue after work.

Speaker-Oriented Classroom Acoustics Design Guidelines in the Context of Current Regulations in European Countries

Summary Most European countries have regulatory requirements or guidelines for reverberation time in classrooms which have the goal of enhancing speech intelligibility and reducing noise levels in schools. At the same time, school teachers suffer frequently from voice problems due to high vocal load experienced at work. With the aim of improving working conditions for teachers, this article presents guidelines for classroom acoustics design that meet simultaneously criteria of vocal comfort and speech intelligibility ,w hich may be of use in future discussions for updating regulatory requirements in classroom acoustics. Tw or oom acoustic parameters are shown relevant for as peaker: the voice support, linked to vocal effort, and the decay time derive df rom an oral-binaural impulse response, linked to vocal comfort. Theoretical prediction models for room-averaged values of these parameters are combined with am odel of speech intelligibility based on the useful-to-detrimental ratio and empirical models of signal-to-noise ratio in classrooms in order to derive classroom acoustic guidelines, taking into account physical volume restrictions linked to the number of students present in ac lassroom. The recommended values of reverberation time in fully occupied classrooms for flexible teaching methods are between 0.45 sa nd 0.6 s( between 0.6 and 0.7 si na nu noccupied bu tf urnished condition )f or classrooms with less than 40 students and volumes belo w2 10 m 3 .W hen designing larger classrooms, ad edicated acoustic study taking into account considerations about geometry ,m aterial and speaker/audience placements should be made, which can help to increase the voice support and reduce the vocal effort.

Blind estimation of reverberation time in classrooms and hospital wards

This paper investigates blind Reverberation Time (RT) estimation in occupied classrooms and hospital wards. Measurements are usually made while these spaces are unoccupied for logistical reasons. However, occupancy can have a significant impact on the rate of reverberant decay. Recent work has developed a Maximum Likelihood Estimation (MLE) method which utilises only passively recorded speech and music signals, this enables measurements to be made while the room is in use. In this paper the MLE method is applied to recordings made in classrooms during lessons. Classroom occupancy levels differ for each lesson, therefore a model is developed using blind estimates to predict the RT for any occupancy level to within ±0.07s for the mid-frequency octave bands. The model is also able to predict the effective room and per person absorption area.Ambient sound recordings were also carried out in a number of rooms in two hospitals for a week. Hospital measurements are more challenging as the occurrence of free reverberant decay is rarer than in schools and the acoustic conditions may be non-stationary. However, by gaining recordings over a period of a week, estimates can be gained within ±0.07s. These estimates are representative of the times when the room contains the highest acoustic absorption. In other words when curtains are drawn, there are many visitors or perhaps a window may be open.

Classroom Reverberation Time Based on the Sabine Equation

Classroom Reverberation Time Based on the Sabine Equation

Students and Soundwaves: Five Strategies to Promote Good Classroom Acoustics

Students and Soundwaves: Five Strategies to Promote Good Classroom Acoustics

Classroom acoustics in public schools: A case study

The acoustic quality of a standard classroom (Standard 23) of the public school system in the city of Curitiba has been evaluated. This standard has a central circulation aisle with two classrooms in each side. Each room has windows to the outside and to the internal aisle. Additionally, the aisle has a 6-m-high zenithal skylight, together composing the building’s main lighting and ventilation system. But, Standard 23 lacks acoustic quality of the classrooms. In order to assay this, measurements have been performed under several conditions, using the Building Acoustics System of Bruel &amp; Kjaer. The measured reverberation time (RT) of the four classrooms for a frequency of 500 Hz was: 1.65 s (empty classroom), 1.15 s (20 students in the room), and 0.76 s (40 students). According to WHO recommendations, the ideal RT in classrooms should be around 0.6 s. DIN 18041 establishes an RT between 0.8 and 1.0 s, to allow for adequate intelligibility. Background noise in an empty room was 63.3 dB (A), above the limit established by the Brazilian standard of acoustic comfort: 40 dB (A). The reaction of students and teachers has indicated that the main source of acoustic discomfort is the noise generated by the neighboring classrooms.

Estimating reverberation time in classrooms by the power method

The Sabin equation relates reverberation time to room volume and absorption. If an acoustic source of known power is placed in a room, the absorption is also related to the power per bandwidth, volume, and pressure. Combining the Sabin equation with the power equation and solving for reverberation time yields a relationship for reverberation time as a function of volume, pressure, and the power of the source. This approach has been reported to deviate from the decay method at low frequency. In a laboratory reverberation room, it yielded reasonable results in the frequency range of interest in classrooms. Reasonable results were also achieved in real classrooms in the 500- to 2000-Hz frequency range. Based on these findings, it may be possible to make acceptable reverberation time measurements in less time with less sophisticated instrumentation than the decay method.