Evaluation of acoustical conditions for speech communication in working elementary school classrooms

Detailed acoustical measurements were made in 41 working elementary school classrooms near Ottawa, Canada to obtain more representative and more accurate indications of the acoustical quality of conditions for speech communication during actual teaching activities. This paper describes the room acoustics characteristics and noise environment of 27 traditional rectangular classrooms from the 41 measured rooms. The purpose of the work was to better understand how to improve speech communication between teachers and students. The study found, that on average, the students experienced: teacher speech levels of 60.4 dB A, noise levels of 49.1 dB A, and a mean speech-to-noise ratio of 11 dB A during teaching activities. The mean reverberation time in the occupied classrooms was 0.41 s, which was 10% less than in the unoccupied rooms. The reverberation time measurements were used to determine the average absorption added by each student. Detailed analyses of early and late-arriving speech sounds showed these sound levels could be predicted quite accurately and suggest improved approaches to room acoustics design.     

Rating,ranking, and understanding acoustical quality in university classrooms

Nonoptimal classroom acoustical conditions directly affect speech perception and, thus, learning by students. Moreover, they may lead to voice problems for the instructor, who is forced to raise his/her voice when lecturing to compensate for poor acoustical conditions. The project applied previously developed simplified methods to predict speech intelligibility in occupied classrooms from measurements in unoccupied and occupied university classrooms. The methods were used to predict the speech intelligibility at various positions in 279 University of British Columbia (UBC) classrooms, when 70% occupied, and for four instructor voice levels. Classrooms were classified and rank ordered by acoustical quality, as determined by the room-average speech intelligibility. This information was used by UBC to prioritize classrooms for renovation. Here, the statistical results are reported to illustrate the range of acoustical qualities found at a typical university. Moreover, the variations of quality with relevant classroom acoustical parameters were studied to better understand the results. In particular, the factors leading to the best and worst conditions were studied. It was found that 81% of the 279 classrooms have "good," "very good," or "excellent" acoustical quality with a "typical" (average-male) instructor. However, 50 (18%) of the classrooms had "fair" or "poor" quality, and two had "bad" quality, due to high ventilation-noise levels. Most rooms were "very good" or "excellent" at the front, and "good" or "very good" at the back. Speech quality varied strongly with the instructor voice level. In the worst case considered, with a quiet female instructor, most of the classrooms were "bad" or "poor." Quality also varies with occupancy, with decreased occupancy resulting in decreased quality. The research showed that a new classroom acoustical design and renovation should focus on limiting background noise. They should promote high instructor speech levels at the back of the classrooms. This involves, in part, limiting the amount of sound absorption that is introduced into classrooms to control reverberation. Speech quality is not very sensitive to changes in reverberation, so controlling it for its own sake should not be a design priority.     

Effect of occupancy on acoustical conditions in university classrooms

Acoustical measurements were made in 12 university classrooms with and without occupants at Kangwon National University (KNU), Korea to investigate how the occupants influence the acoustical conditions of the classrooms. The mean sound absorption per occupant was calculated from the measured T₃₀ values and compared in two different groups of classrooms (6 reflective and 6 absorptive classrooms). At 250 and 500 Hz, the mean sound absorption per occupant was nearly the same for both groups of classrooms, but not in the other octave bands. The results showed that the effect of the added absorption of occupants is dependent on the acoustical conditions of the classroom. The changes in acoustical parameter values, due to added occupants in the classrooms, tended to be largest for the more reflective classrooms. The occupants may contribute to achieving more ideal reverberation times for speech (typically 0.4–0.7 s in classrooms) in the more reflective classrooms, but not in the more absorptive classrooms. A simple process is described to predict the expected effects of adding occupants to other classrooms based on the total sound absorption of unoccupied rooms.     

Speech related acoustical parameters in classrooms and their relationships

A survey on the speech related acoustical parameters in the Hong Kong classrooms having standardized architectural layouts is carried out in the present study. Results suggest that these acoustical parameters are highly correlated with each other even across different octave bands. It is also found that the relationships between parameters of different kinds do not depend on the frequency bands. Besides, the present results indicate that the sound pulse decay inside a not very reverberant classroom consists of an initial fast decay, leading to deviations of the field survey results from those predicted by the exponential decay under the uniform sound energy decay assumption. It is believed that the strong correlations between the various speech related acoustical parameters and the regression information obtained in the present study can help the estimation of the speech quality of the classrooms in the design stage.     

The intelligibility of speech in elementary school classrooms

This is the second of two papers describing the results of acoustical measurements and speech intelligibility tests in elementary school classrooms. The intelligibility tests were performed in 41 classrooms in 12 different schools evenly divided among grades 1, 3, and 6 students (nominally 6, 8, and 11 year olds). Speech intelligibility tests were carried out on classes of students seated at their own desks in their regular classrooms. Mean intelligibility scores were significantly related to signal-to-noise ratios and to the grade of the students. While the results are different than those from some previous laboratory studies that included less realistic conditions, they agree with previous in-classroom experiments. The results indicate that +15 dB signal-to-noise ratio is not adequate for the youngest children. By combining the speech intelligibility test results with measurements of speech and noise levels during actual teaching situations, estimates of the fraction of students experiencing near-ideal acoustical conditions were made. The results are used as a basis for estimating ideal acoustical criteria for elementary school classrooms.     

Speech intelligibility studies in classrooms

Speech intelligibility tests and acoustical measurements were made in ten occupied classrooms. Octave-band measurements of background noise levels, early decay times, and reverberation times, as well as various early/late sound ratios, and the center time were obtained. Various octave-band useful/detrimental ratios were calculated along with the speech transmission index. The interrelationships of these measures were considered to evaluate which were most appropriate in classrooms, and the best predictors of speech intelligibility scores were identified. From these results ideal design goals for acoustical conditions for classrooms were determined either in terms of the 50-ms useful/detrimental ratios or from combinations of the reverberation time and background noise level.     

Objective and subjective evaluation of acoustic comfort in classrooms: A comparative investigation of vernacular and modern school classroom in Kerala

This paper reports a comparative investigation on acoustic comfort of classrooms in vernacular and modern school buildings in tropical warm humid climate. In this type of climate the intrusion of external noise into the classrooms along with cross ventilation is unavoidable. Preliminary investigation on the evaluation of acoustic comfort carried in secondary schools located in Kollam district of Kerala State in India have been reported. As a step ahead, in order to understand the performance of vernacular school classroom in comparison with that of a modern classroom, an initial survey was conducted in classrooms of ten vernacular and 10 modern schools. Further a detail investigation was carried out in a vernacular and modern school building located in the same site. The study was conducted by measuring the two important acoustic parameters viz., background noise and reverberation time which affect the acoustical comfort in the classrooms. The level of satisfaction of the users was evaluated through questionnaires distributed to teachers and students. The result of the scientific analysis was compared to user’s response. The study reveals that modern classrooms are more preferred than vernacular classrooms acoustically, by the teachers and students. The study also confirms a strong need of improving the acoustical comforts in the classrooms.     

Case-study evaluations of the acoustical designs of renovated university classrooms

The acoustical characteristics of 14 university classrooms at the University of British Columbia were measured before and after renovation—seven of these are discussed in detail here. From these measurements, and theoretical considerations, values of quantities used to assess each classroom configuration were predicted, and used to evaluate renovation quality. Information on each renovation was determined with the help of the university campus-planning office and/or the project acoustical consultant. These were related to the evaluation results in order to determine the relationship between design and acoustical quality. The criteria focused on the quality of verbal communication in the classrooms. Room-average Speech Intelligibility (SI) and its physical correlate, Speech Transmission Index (STI), were used to quantify verbal-communication quality. A simplified STI-calculation procedure was applied. The results indicate that some renovations were beneficial, others were not. Verbal-communication quality varied from ‘poor’ to ‘good’. The effect of a renovation depends on a complex interplay between changes in the reverberation and changes in the signal-to-noise level difference, as affected by sound absorption and the source outputs. Renovations which reduce noise are beneficial unless signal-to-noise level differences remain optimal. Renovations often put too much emphasis on adding sound absorption to control reverberation, at the expense of lower speech levels, particularly at the backs of classrooms. The absorption and noise contributed by room occupants has apparently often been neglected.     

Subjective assessment of listening environments in university classrooms: perceptions of students

A questionnaire is developed to evaluate perception of the listening environment by university students. The objectives were to develop a questionnaire-based measurement tool, derive a measure of perceived classroom-listening quality, use the questionnaire to investigate factors that enhance, impair, or do not affect perceived listening quality, and consider the implications for classroom design. The questionnaire was administered to over 5700 students in 30 classrooms at one university. Physical and acoustical measurements were also performed in each classroom. The questionnaire included items that recorded aspects of student perception, as well as individual, course-, and instructor-specific factors. Responses to 19 perception items generated a perception of listening ease (PLE) score for each student and a classroom-average score. Decreased PLE was associated with women, English-second-larguage students, those with hearing impairment, students not interested in the course material, and those who found the material difficult. Increased PLE was associated with higher speech transmission index, acceptable lighting, temperature and seating, better instructor voice, increased visual-aid use, and easier course material. Results indicate that PLE is a useful measure of student perception of the classroom-listening environment, and that optimal classroom acoustical design must take into consideration "in-use" conditions, as well as classroom physical characteristics.     

Assessment model of classroom acoustics criteria for enhancing speech intelligibility and learning quality

In this paper, a new classroom acoustics assessment model (CAAM) based on analytic hierarchy process (AHP) for enhancing speech intelligibility and learning quality is proposed. The model is based on five main criteria that affect the learning process and related to classrooms acoustical properties. These include classroom specifications, noise sources inside and outside the classroom, teaching style, and vocal effort. The priority and weights of these major criteria along with their alternatives are identified using the views of students, staff, education consultants, and expertise by using a developed questionnaire, and the AHP methodology. This model can be considered as a helpful framework enabling universities decision makers to take effective decisions on classroom acoustics treatment issues. It also provides colleges’ higher authorities the suitable guidelines that help for determining necessary requirements that help to raise the quality and efficiency of the educational environment; in order to reach an excellent learning environment; and hence increasing students learning outcomes.     

Investigating the acoustics of a sample of open plan and enclosed Kindergarten classrooms in Australia

Open plan classrooms, where several class bases share the same space, have recently re-emerged in Australian primary schools. This study compared the acoustics of four different Kindergarten classrooms: an enclosed classroom with 25 students, a double classroom with 44 students, a linear fully open plan triple classroom with 91 students, and a semi-open plan K-6 classroom with 205 students. Ambient noise levels, intrusive noise levels, occupied background noise levels, and teacher’s speech levels were recorded during different activities. Room impulse responses using logarithmic sweeps were also recorded for different teaching scenarios. From these recordings, signal-to-noise ratios, speech transmission index scores, and reverberation times were calculated. The results revealed much higher intrusive noise levels in the two largest open plan classrooms, resulting in signal-to-noise ratios and speech transmission index scores to be well below those recommended in classrooms with students of this age. Additionally, occupied background noise levels in all classrooms were well above recommended levels. These results suggest noise in classrooms needs to be better controlled, and open plan classrooms are unlikely to be appropriate learning environments for young children due to their high intrusive noise levels. The impact of noise on children’s learning and teacher’s vocal health are discussed.     

The impact of urban noise on primary schools. Perceptive evaluation and objective assessment

This paper aims to assess the impact of environmental noise in the vicinity of primary schools and to analyze its influence in the workplace and in student performance through perceptions and objective evaluation. The subjective evaluation consisted of the application of questionnaires to students and teachers, and the objective assessment consisted of measuring in situ noise levels. The survey covered nine classes located in three primary schools. Statistical Package for Social Sciences was used for data processing and to draw conclusions. Additionally, the relationship of the difference between environmental and background noise levels of each classroom and students with difficulties in hearing the teacher’s voice was examined. Noise levels in front of the school, the schoolyard, and the most noise-exposed classrooms (occupied and unoccupied) were measured. Indoor noise levels were much higher than World Health Organization (WHO) recommended values: L_Aeq,30min averaged 70.5 dB(A) in occupied classrooms, and 38.6 dB(A) in unoccupied ones. Measurements of indoor and outdoor noise suggest that noise from the outside (road, schoolyard) affects the background noise level in classrooms but in varying degrees. It was concluded that the façades most exposed to road traffic noise are subjected to values higher than 55.0 dB(A), and noise levels inside the classrooms are mainly due to the schoolyard, students, and the road traffic. The difference between background (L_A95,30min) and the equivalent noise levels (L_Aeq,30min) in occupied classrooms was 19.2 dB(A), which shows that students’ activities are a significant source of classroom noise.     

A study on the optimal English speech level for Chinese listeners in classrooms

Speech intelligibility in classrooms affects the learning efficiency of students directly, especially for the students who are using a second language. The speech intelligibility value is determined by many factors such as speech level, signal to noise ratio, and reverberation time in the rooms. This paper investigates the contributions of these factors with subjective tests, especially speech level, which is required for designing the optimal gain for sound amplification systems in classrooms. The test material was generated by mixing the convolution output of the English Coordinate Response Measure corpus and the room impulse responses with the background noise. The subjects are all Chinese students who use English as a second language. It is found that the speech intelligibility increases first and then decreases with the increase of speech level, and the optimal English speech level is about 71 dBA in classrooms for Chinese listeners when the signal to noise ratio and the reverberation time keep constant. Finally, a regression equation is proposed to predict the speech intelligibility based on speech level, signal to noise ratio, and reverberation time.     

A survey of acoustic conditions in semi-open plan classrooms in the United Kingdom

This paper reports the results of a large scale, detailed acoustic survey of 42 open plan classrooms of varying design in the UK each of which contained between 2 and 14 teaching areas or classbases. The objective survey procedure, which was designed specifically for use in open plan classrooms, is described. The acoustic measurements relating to speech intelligibility within a classbase, including ambient noise level, intrusive noise level, speech to noise ratio, speech transmission index, and reverberation time, are presented. The effects on speech intelligibility of critical physical design variables, such as the number of classbases within an open plan unit and the selection of acoustic finishes for control of reverberation, are examined. This analysis enables limitations of open plan classrooms to be discussed and acoustic design guidelines to be developed to ensure good listening conditions. The types of teaching activity to provide adequate acoustic conditions, plus the speech intelligibility requirements of younger children, are also discussed.     

The effect of ambient noise on speech intelligibility in classrooms

Intelligibility tests were performed by teachers and pupils in classrooms under a variety of (road traffic) noise conditions. The intelligibility scores are found to deteriorate at (indoor) noise levels exceeding a critical value of — 15 dB with regard to a teacher's long-term (reverberant) speech level. The implications for external noise levels are discussed: typically, an external noise level of 50 dB(A) would imply that the critical indoor level is exceeded for about 20 per cent of teachers.     

Measurement of acoustical characteristics of mosques in Saudi Arabia

The study of mosque acoustics, with regard to acoustical characteristics, sound quality for speech intelligibility, and other applicable acoustic criteria, has been largely neglected. In this study a background as to why mosques are designed as they are and how mosque design is influenced by worship considerations is given. In the study the acoustical characteristics of typically constructed contemporary mosques in Saudi Arabia have been investigated, employing a well-known impulse response. Extensive field measurements were taken in 21 representative mosques of different sizes and architectural features in order to characterize their acoustical quality and to identify the impact of air conditioning, ceiling fans, and sound reinforcement systems on their acoustics. Objective room-acoustic indicators such as reverberation time (RT) and clarity (C50) were measured. Background noise (BN) was assessed with and without the operation of air conditioning and fans. The speech transmission index (STI) was also evaluated with and without the operation of existing sound reinforcement systems. The existence of acoustical deficiencies was confirmed and quantified. The study, in addition to describing mosque acoustics, compares design goals to results obtained in practice and suggests acoustical target values for mosque design. The results show that acoustical quality in the investigated mosques deviates from optimum conditions when unoccupied, but is much better in the occupied condition.     

Perceived pitch of whispered vowels-relationship with formant frequencies: A preliminary study

To clarify the role of formant frequency in the perception of pitch in whispering, we conducted a preliminary experiment to determine (1.) whether speakers change their pitch during whispering; (2.) whether listeners can perceive differences in pitch; and (3.) what the acoustical features are when speakers change their pitch. The listening test of whispered Japanese speech demonstrates that one can determine the perceived pitch of vowel /a/ as ordinary, high, or low. Acoustical analysis revealed that the perception of pitch corresponds to some formant frequencies. Further data with synthesized whispered voice are necessary to confirm the importance of the formant frequencies in detail for perceived pitch of whispered vowels.     

Comparison between measured and calculated parameters for the acoustical characterization of small classrooms

This paper presents a comparison between measured and calculated acoustical parameters in eight high school classrooms. The mid frequency unoccupied and occupied reverberation times and the 1 kHz sound propagation (SP) of the reverberant and total speech levels in occupied classrooms were compared with analytical and numerical predictions. The ODEON 6.5 code and the Sabine formula gave the most accurate results for reverberation time in the empty classrooms with overall relative differences of 8.1% and 9.7%, respectively. With students present, the Eyring and Sabine formulas and Hodgson’s empirical model resulted to be the most accurate with relative differences of 11.1%, 13.2% and 13.6%, respectively. The reverberant speech levels decrease with increasing distance from the source at rates varying from −1.21 to −2.62 dB/distance doubling, and the Hodgson model fits the slope values quite well. The best predictions of the SP of the reverberant and total speech levels are shown, in order of accuracy, for the ODEON code, the Barron and Lee theory and the classical diffuse field theory. Lower rms errors were found when the measured total acoustic absorptions were used. The lowest rms error of 1.4 dB for the SP of the total speech level were found for both the ODEON code and the Barron and Lee theory.     

Experimental investigation of the effects of the acoustical conditions in a simulated classroom on speech recognition and learning in children

The potential effects of acoustical environment on speech understanding are especially important as children enter school where students' ability to hear and understand complex verbal information is critical to learning. However, this ability is compromised because of widely varied and unfavorable classroom acoustics. The extent to which unfavorable classroom acoustics affect children's performance on longer learning tasks is largely unknown as most research has focused on testing children using words, syllables, or sentences as stimuli. In the current study, a simulated classroom environment was used to measure comprehension performance of two classroom learning activities: a discussion and lecture. Comprehension performance was measured for groups of elementary-aged students in one of four environments with varied reverberation times and background noise levels. The reverberation time was either 0.6 or 1.5 s, and the signal-to-noise level was either +10 or +7 dB. Performance is compared to adult subjects as well as to sentence-recognition in the same condition. Significant differences were seen in comprehension scores as a function of age and condition; both increasing background noise and reverberation degraded performance in comprehension tasks compared to minimal differences in measures of sentence-recognition.