Speech Intelligibility In Classrooms Research Articles

Influence of indoor and outdoor noises on the speech intelligibility in classrooms

There are many noise sources inside the classrooms such as heating, ventilating, and air-conditioning(HVAC) noises. Also, there are outdoor noises near classrooms such as road traffic noises. Under these situations, teachers are using loudspeaker system in order to enhance the speech transmission. The present study aims to investigate the students’ subjective responses to teacher’s speech under many different noise situations. in order to this, questionnaire survey was undertaken to 60 students in two different classrooms. They were asked to mark their subjective listening comprehension and speech intelligibility in 5-points scale at every cases when three conditions were changed including opening status of doors and windows, operating HVAC system, and usage of loudspeaker system. Also, sound levels were measured in each case. As a result, it was found that only 17% of subjects responded that they were prevented from noises from outdoor and HVAC system. Also, it was responded that using loudspeaker system can enhance the listening conditions 2.7 times more than normal condition. Nevertheless, there are 33% of negative responses to loudspeaker system due to the artificial tone of speech. Thus, it can be concluded that indoor and outdoor noises cause by opening windows and operating HVAC system do not affect student’s speech intelligibility much in general cases, Also, using loudspeaker system in small classroom should be used cautiously considering students’ preferences.

Effect of varying corridor parameters on signal-to-noise ratio in classrooms

Corridors have a crucial effect on classroom acoustics, but its study is generally ignored. After examining the acoustic performance of a coupled space comprising a corridor and two classrooms, a new method for calculating the signal-to-noise ratio (SNR) by the analysis of the energy distribution is proposed in this paper. Numerical experiments are conducted using the finite element software COMSOL Multiphysics. Various parameters are explored using the proposed numerical model to determine their effect on the SNR at different receiving points in a classroom. It was observed that factors such as the corridor width, absorption of the corridor carpet materials, and aperture area (i.e., classroom doors) affect room acoustics. The results show that an absorption treatment of the corridor has a significant effect on classroom acoustic performance. The findings of this study help us understand various metrics of acoustic performance in extended coupled spaces, such as speech intelligibility in classrooms and offices.

Intelligibility of dysphonic speech in primary schools

School children need clear auditory signals and low background noise to learn. When classroom acoustics are poor, teachers often compensate by raising their voices, usually with limited effect against background noise, and, long-term, this makes vocal overuse the primary cause (60%) of the high prevalence of voice problems in teachers. Speech intelligibility tests were performed in primary schools with normal hearing students using words produced by an actor with normal voice quality and simulating a dysphonic voice. The speech was played by a Head and Torso Simulator. Artificial classroom noise and classrooms with different reverberation times were used to obtain a range of Speech Transmission Index from 0.2 to 0.7 (from bad to good). Results showed a statistically significant decrease in intelligibility when the speaker was dysphonic with a maximum of 15% intelligibility loss. This study extends an important pairing of problems related to student learning: classroom acoustics and teachers with voice disorders. It provides important insights into the enormous variability in speech intelligibility in classrooms by characterizing students’ intelligibility when students receive degraded auditory input. The degraded auditory input results from the intersection of classroom acoustics and poor teacher voice quality

The effect of low frequency reverberation on Chinese speech intelligibility in two classrooms

The previous study had investigated the students’ speech perceptions in two primary school classrooms with similar reverberation time and found that the speech intelligibility in a classroom was better than that in other one. It is speculated that due to difference in the improvement in low frequency reverberation. In this study, the reverberation time and speech transmission index were obtained and compared from these two classrooms by simulated. The subjective Chinese speech intelligibility was evaluated through simulated binaural room impulse responses. The effect of low frequency reverberation on Chinese speech intelligibility in two classrooms was discussed. The result shows that improving the low frequency characteristic of reverberation time can be helpful to improve the Chinese speech intelligibility in classroom.

How much COVID-19 face protections influence speech intelligibility in classrooms?

The ongoing pandemic caused by the COVID-19 virus is challenging many aspects of daily life. Several personal protective devices have become essential in our lives. Face protections are mostly used in order to stop the air aerosol coming out of our mouths. Nevertheless, this fact may also have a negative effect on speech transmission both in outdoor and indoor spaces. After a severe lockdown, classes have now started again. The adoption of face protection by teachers is either recommended or mandatory even though this is affecting speech intelligibility and thus students’ comprehension. This study aims to understand how protections may affect the speech transmission in classrooms and how this could be influenced by the several typologies of face protections. An experimental campaign was conducted in a classroom in two different reverberant conditions, measuring and comparing the variation in speech transmission and sound pressure level at different receiver positions. Furthermore, a microphone array was used to investigate the distribution of the indoor sound field, depending on the sound source. Results clearly show how different types of personal protection equipment do affect speech transmission and sound pressure level especially at mid-high frequency and that the source emission lobes vary when wearing certain types of personal devices.

Artificial Software Complex "Artificial Head". Part 2 Evaluation of Speech Intelligibility in Classrooms

Experimental studies of the use of the developed hardware and software tool “Artificial Head” for two-channel estimation of the intelligibility of the speech distorted by reverberation have been performed in this paper. The peculiarity of this complex is that it contains electro-acoustic equipment of different quality, including household appliances with mediocre quality features.In the first stage of this evaluation, the response of the room to the test signal is recorded. The test signal was based on the maximum-length sequence (mls) which is a periodic two-level signal of length 216, which corresponds to a signal length of 1.49 s at a sampling rate of 44.1 kHz. This mls-sequence was repeated 17 times during radiation and averaging the last 16 bursts of the cross-correlation estimates have been made to increase the signal-to-noise ratio by 12 dB in the calculation of the room impulse response.The calculation of the cross-correlation function of the response and the test signal was performed in the second stage, while the correction of the frequency characteristic of the measuring path was performed by it dividing by the amplitude-frequency characteristic of the loudspeaker-microphone subsystem. To improve the accuracy of the calculations, the result of such division was multiplied by the regularization factor in the form of a Hann window.In the third stage, the modulation coefficients were calculated according to the Schroeder formula, using the room impulse response estimate. In the fourth, last step, speech intelligibility was evaluated by a modulation or formant-modulation method. The results of the speech intelligibility evaluation in two lecture rooms of small and medium size showed that the speech intelligibility in the middle of the room can be less than that near the wall of the room. These results are in line with the results of previous studies, where speech intelligibility has been evaluated by objective and subjective methods for another lecture room. It should be noted that although the estimates of the widely used C50 coefficient are consistent with the estimates of speech intelligibility, the phenomenon of increasing speech intelligibility near the walls of the room is more pronounced when applying the speech intelligibility estimates.The results presented in this paper indicate that the usefulness of early reflections in the room is different in different parts of the room. This important fact must be taken into account both in the design and the reconstruction of the lecture rooms.

Comparative study of acoustical indices and speech perception of students in two primary school classrooms with an acoustical treatment

Objective acoustical indices and subjective speech perception of students were investigated and compared in two different classrooms before and after an acoustical treatment. The treatment in the present study refers to the installation of sound absorption materials on the ceilings in two primary school classrooms. The results showed that the reverberation time after acoustical treatment was reduced, while the early-to-late sound ratio and the speech transmission index were improved. The subjective speech intelligibility in classrooms was also enhanced. Subjective survey showed that most of the students preferred learning in the classrooms after acoustical treatment. They reported that higher concentration is because the speeches of the teachers were much clear in the treated classroom. However, subjective speech perception of the students has some discrepancies between the two classrooms. The perception of the students in Classroom A was better than that in Classroom B. Sixty-two percent (61.9%) of the students prefer to study in the classroom A after acoustical treatment, but only 46.3% of the students prefer to study in the Classroom B. Results show that exceeding low-frequency reverberation in the classroom may significantly mask speech signals and have effect on the student’s speech perception in classroom, even though the traditional criteria of RT and C50 at mid-frequencies are similar.

언어명료도에 기반한 창문 개방 조건 교실의 배경소음 기준 고찰

Speech intelligibility in classrooms, determined by signal-to-noise ratio and room acoustics quality, is important for communication between teachers and students. This work reports on the current situation of speech intelligibility evaluated using useful-to-detrimental ratio (U50) in 12 unoccupied classrooms near roads. To examine the influence of traffic noise transmitted into classrooms on the speech intelligibility, on-site measurements were carried out according to closed and open window conditions. The results showed that the average U50 values were 2.68 ㏈ and –3.73 ㏈ for closed and open window conditions, respectively, indicating the importance of background noise control in classrooms. Based on the measured U50 values and the precedent study, proper background noise levels in classrooms in case of an open window were 43.3 ㏈A and 47.8 ㏈A to meet the minimum level for a “good” class (USUB50/SUB = 1.5 ㏈) and the middle level for a “fair” class (USUB50/SUB = –1.0 ㏈).

Comparison of Two Types of Combined Measures, STI and U50, for Predicting Speech Intelligibility in Classrooms

AbstractThe present study reports on the speech intelligibility as measured by speech transmission index (STI) and useful-to-detrimental sound ratios (U50) in university classrooms. Acoustic measurements were made in 12 quietly occupied university classrooms. The measured impulse responses of the classrooms were used to determine the modulation transfer function, m(F), for the STI calculation according to IEC 60268-16. U50values were determined from both signal-to-noise ratios (SNR) and C50values. The mean STI and frequency-weighted U50values for the 12 occupied classrooms were strongly linearly related. The results showed that classrooms with U50values of about +0.5 dB correspond to STI values of 0.60, indicating ‘good’ acoustical conditions for speech intelligibility. The results illustrate that the U50measure can be a more practically useful means of assessing and understanding room acoustics conditions for real speech communication in active classrooms.

Effect of outdoor noise and façade sound insulation on indoor acoustic environment of Italian schools

The paper deals with the effect of outdoor noise mainly due to traffic and façade sound insulation on indoor noise level and speech intelligibility in classrooms. Results refer to the complete building stock of the Italian school buildings based on a census of the Italian Ministry of Education.The selected school sample consists of more than one hundred Italian schools of all levels (from nursery to upper secondary school) located in three Italian regions, built in different time periods and with different building techniques. The selected sample is representative of typical Italian schools.The façade sound insulation and the reverberation time of each school have been measured. The average outdoor noise level of about half the investigated schools has been measured and, for each school, the age of the building and the main characteristics of the façade have been listed (kind of glass, kind of ventilation, windows size, etc.). Based on these data, the correlations between both the main characteristics of the façades and the year of construction and the façade sound insulation have been investigated. Moreover, the influence of the noise coming from outdoor on the indoor noise level, speech intelligibility and speech to noise ratio have been analysed with reference to the situations both before and after the works carried out to improve the acoustic performances of façades.Results show that the indoor sound pressure level due to traffic noise is considerably reduced after the improvement of the façade acoustic insulation, while further treatments to indoor surfaces should be necessary to reduce internal reverberation time and to improve speech intelligibility.

Optimizing the signal to noise ratio in classrooms using passive acoustics

Adults with normal hearing require a roughly 0 dB signal-to-noise ratio (SNR) for good speech intelligibility in classrooms and lecture halls. However, values in excess of 15 dB are needed to compensate for neurological immaturity, sensorineural and conductive hearing losses, language proficiency, and excessive reverberation. ANSI 12.60 addresses ways to lower the noise interference due to background levels and reverberation time. However, simply reducing the mid-high frequency reverberation time is not sufficient and may lead to masking of the high frequency consonant information, needed for speech intelligibility, with lower frequency vowel sounds. Research has shown that increasing the signal by including early reflections is also needed. This presentation will discuss a classroom design, along with several potential acoustical treatments, which aims to passively increase the SNR and improve speech intelligibility. These acoustic tools include a multi-layer, broad bandwidth absorptive panel, a hybrid diffusive/absorptive panel, an absorptive wood system simultaneously offering early reflections and mid-low frequency sound absorption and an LED lighting fixture system that simultaneously provides light and sound diffusion, as well as variable color and intensity for task lighting that has been shown to improve reading speed, increase test scores, and reduce hyperactivity.

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 71dBA 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.

Heterogeneous Speech Prediction Using LDA Classifiers

Classroom speech intelligibility has become one of the main concerns in schools and other learning institutions development nowadays. This is because the qualities of student’s perceptions towards teacher are essentials in learning development. Measures have been introduced by the acoustical association to tackle the speech intelligibility problems in the classroom such as room renovations. Room’s acoustics standards have been introduced in several countries but still the questions on whether the standards fits on every classroom in different countries are still arise. Studies have also shown that most of the researches that have been conducted were only focusing on the conventional type classroom which depends only on the teacher’s vocal power. This paper will formulate the measurement protocol on measuring the speech intelligibility in the sound reinforced (multiple speaker) classroom. Finally it was found that the speech intelligibility in the sound reinforced classroom is better than the conventional classroom by using Linear Discriminant Analysis.

Intelligibility assessment in elementary school classrooms from binaural room impulse responses measured with a childlike dummy head

In a classroom, especially for those intended for small children, speech intelligibility is a basic issue for learning efficacy. As it is well known, applying articulation tests (AT’s) is the best way to assess room’s speech intelligibility. However, the technique is expensive and takes a rather long time to be completed. In this paper, a new technique to assess classroom speech intelligibility is presented, which does not require the application of AT’s inside the classroom. The room binaural impulse response, produced by a sweep sine signal and emitted by an artificial speaker (AS), is recorded with a dummy head. Since small children are involved, the binaural recording was performed with a childlike dummy head, with a size corresponding, roughly, to that of a 10years old child. The binaural measurements were also made using an adult dummy head for comparison purposes. The measured binaural impulse responses were convolved with anechoic signals containing the enunciation of monosyllables. The background noise measured in the room is then added and the result is convolved again with a headphone impulse response, generating an acoustical virtual reality – the auralizations. The resulting binaural signals are applied to subjects of the same age in virtual AT’s. To validate the technique, actual AT’s using the same anechoic lists of monosyllables emitted by the AS inside the classroom were performed. The technique was applied in three schools to students of different level classrooms. The results show that the proposed technique presents good reliability to assess classroom intelligibility when the measurements are made with the childlike dummy head. For virtual AT’s obtained with the adult dummy head, however, it was verified that the children ability to recognize the monosyllables was much lower than that with the childlike dummy head. This is a consequence of the pronounced differences between the head related impulse responses for an adult and a child, resulting in distinct binaural impulse responses.

Effect of the Inter-aural Level Differences on the Speech Intelligibility Depending on the Room Absorption in Classrooms

본 논문은 교실 및 회의실과 같은 소규모 공간에서 건축 마감재료에 의해 발생할 수 있는 좌우귀의 음량 차이가 사람의 청각적 음성명료도에 미치는 영향에 대하여 규명하고자 하였다. 이를 위해 대학교 강의실의 좌,우 측벽에 흡음재를 설치하였으며, 양이 녹음 시스템을 이용하여 좌측귀와 우측귀의 음압레벨을 각각 측정하였다. 또한 흡음재를 설치하기 전과 후 강의실에서 정상 청력의 대학생 20명을 대상으로 음절테스트를 수행하여 양이간 음량차이에 따른 음성명료도를 조사하였다. 그 결과 측벽에 흡음재를 설치 한 후 벽체에 가까워질수록 양이간 음량차가 크게 발생한다는 점을 알 수 있었으며 일부 수음점에서는 최소변화감지폭인 3 dB 이상 차이가 발생하는 곳도 있었다. 또한 측정점별 양이간 음량차와 음절테스트 점수의 상관관계를 분석한 결과 상관관계 계수가 약 -0.441로 유의한 결과를 나타내었다. 따라서 양이간 음량차가 강의실의 음성명료도에 영향을 미칠 수 있음을 알 수 있었다. The present study investigates the effect of the inter-aural level difference(ILD) on the syllable articulation test in classrooms which can be occurred by the absorption of interior surfaces. In order to do this, the sound absorbing materials were installed in the classroom and sound pressure level(SPL) at each ear was measured using binaural recording systems. Also, syllable articulation tests were carried out at a classroom with and without sound absorption materials by 20 students who have normal hearing condition, in order to investigates the effect of the ILD on the speech intelligibility. As a result, it was found that the larger inter-aural level differences was occurred at the nearer positions to lateral walls after sound absorptions were applied to lateral walls in the classroom. At some places, the measured ILD was lager than JND of sound level (3dB). Also, it was shown that the correlation coefficient of inter-aural level difference with the score of syllable test has the significant result(-0.441). Thus, It is concluded that ILD can affect the subjective speech intelligibility in classrooms.

Effect of the inter-aural sound level differences on the speech intelligibility

It was defined from the results of many previous researches that the most effective criterion affecting sound clarity in rooms is the early reflected sound. C80 and D50 were used to evaluate sound clarity in rooms. These parameters are related with the sound energy in function of time and they are monoral indexes which do not count for the spatial information including sound directions. Thus, C80 and D50 do not consider the changes of sound clarity caused by difference of sound energy between left and right ears. The proposed study investigates the effect of the inter-aural sound level difference (ILD) on the speech intelligibility in classrooms which can be occurred by the absorption of interior surfaces. In order to do this, sound levels were measured with inter-aural differences of D50, C80 (ID-D50, ID-C80) using dummy-head binaural recording systems. As a result, it was clearly found that ILD was much increased beyond JND after sound absorptions were implied in room. Also, the correlation coefficient of ILD with the distance from sidewalls has increased from 0.696 to 0.890 after sound absorptions. However, there was not clear difference in other parameters (ID-D50, ID-C80). It is also denoted that the increase of ILD can affect the subjective speech intelligibility as well.

Computer analysis of speech intelligibility in classrooms.

The objective of this research is to study the relationship between classroom characteristics and speech intelligibility in order to optimize the amount of acoustic treatment and its position in the room. A rectangular shaped room was modeled with the ULYSSESS acoustic analysis software. Total sound level, first reflections, the difference between direct and reflected sound, reverberation time, ALCONs, and STI were calculated. The amount of absorption treatment and its position in the room, as well as the number of people in the room, were the variables studied. Results show that the amount of absorption treatment and the number of people in the room were much more important than the position of both the absorbent materials and the students to obtain good intelligibility scores. Nevertheless, for similar intelligibility scores, overall sound level is higher when the amount of absorbent material is controlled, allowing the listeners in the rear to benefit from higher speech levels. A reduction of 78% in the area of absorbent material can be achieved while maintaining the same STI score for all the positions in the room, with an increase in overall sound level of 4–5 dB.

Verifying speech intelligibility in classrooms.

Classroom speech intelligibility has undoubtedly become a hot topic and is capturing attention on all fronts. While there has been widespread adoption of many new guidelines and standards, even the most precise initiatives will not reach their full potential if speech intelligibility is not directly verified in classrooms after they are built. Performance verification ultimately encourages a better final product and provides crucial measured data for validating design methods. To ensure measurable performance, criteria would have to be established at the outset of the design using a metric directly related to speech intelligibility such as speech transmission index. Current guidelines generally focus on reverberation time (RT) and background noise for improving speech communication in classrooms. While low background noise is a necessary component for speech intelligibility, there is not always a direct correlation between RT and speech intelligibility. For instance, improper placement of absorptive treat...

Chinese speech intelligibility at different speech sound pressure levels and signal-to-noise ratios in simulated classrooms

The speech intelligibility in classroom can be influenced by background-noise levels, speech sound pressure level (SSPL), reverberation time and signal-to-noise ratio (SNR). The relationship between SSPL and subjective Chinese Mandarin speech intelligibility and the effect of different SNRs on Chinese Mandarin speech intelligibility in the simulated classroom were investigated through room acoustical simulation, auralisation technique and subjective evaluation. Chinese speech intelligibility test signals recorded in anechoic chamber were convolved with the simulated binaural room impulse responses, and then reproduced through the headphone by different SSPLs and SNRs. The results show that Chinese Mandarin speech intelligibility scores increase with increasing of SSPLs and SNRs within a certain range in simulated classrooms. Chinese Mandarin speech intelligibility scores have no significant difference with SNRs of no less than 15 dBA under the same reverberation time condition.

Optimizing the signal-to-noise ratio in speech rooms using passsive acoustics.

Adults with normal hearing require a roughly 0‐dB signal‐to‐noise ratio for good speech intelligibility in classrooms and lecture halls. However, significantly higher values may be needed to compensate for neurological immaturity, sensorineural and conductive hearing losses, language proficiency, and excessive reverberation. ANSI 12.60 addresses ways to lower the noise interference due to background levels and reverberation time. However, it is also possible to increase the signal, by reflecting or diffusing early reflection. While speech power is delivered in the vowels which are predominately in the 250–500‐Hz frequency range, speech intelligibility is delivered in the consonants, which occur in the 2–4‐kHz frequency range. Therefore, effective core learning designs can incorporate scattering surfaces, rather than surfaces that absorb in the 2–4‐kHz region, on the front wall, lower side walls, and central ceiling areas, to increase the speech signal. The decay time can be controlled with broadband absorption on the perimeter of the ceiling and upper wall surfaces. A computer model analysis of various speech environments will be presented.