Speech Transmission Index Values Research Articles

Influence of Test Room Acoustics on Non-Native Listeners’ Standardized Test Performance

Understanding the impact of room acoustics on non-native listeners is crucial, particularly in standardized English as a foreign language (EFL) proficiency testing environments. This study aims to elucidate how acoustics influence test scores, considering variables overlooked in prior research such as seat position and baseline language proficiency. In this experiment, 42 Japanese university students’ performance on standardized EFL listening tests was assessed in two rooms with distinct acoustic qualities, as determined by the speech transmission index (STI) and reverberation time (RT). The rooms differed significantly in their STI values and RT measurements, with one exhibiting high speech intelligibility qualities of ≥0.66 STI and RT0.5–2kHz < 0.7 s and the other falling below these benchmarks. The findings revealed that listening test scores were consistently higher in the acoustically favorable room across all participants. Notably, the negative effect of poor acoustics was more pronounced for students with lower baseline language proficiency. No significant score differences were observed between front- and rear-seat positions, suggesting that overall room acoustics may be more influential than individual seating locations. The study concludes that acoustics play a significant role in the standardized EFL test performance, particularly for lower-proficiency learners. This highlights the necessity of standardized testing environments to be more carefully selected in order to ensure the fair and reliable assessment of language proficiency.

Indoor acoustic quality of educational buildings in South West Europe: Influence of current ventilation strategies

The quality of the classroom environment has a great impact on the physical and mental health of students and teachers. The COVID-19 pandemic has highlighted the need for new measures and ventilation strategies to be implemented in educational buildings, to ensure indoor air quality in classrooms and to minimise the risk of airborne virus transmission. However, these ventilation protocols can influence the acoustic quality of classrooms and negatively affect students’ speech perception and learning performance. This study presents the results obtained from a field measurement campaign carried out to assess the acoustic characteristics of classrooms of the Fuentenueva Campus (University of Granada) and Azurém Campus (University of Minho). Different ventilation operating scenarios (active and inactive) were assessed to evaluate their impact on the indoor acoustic conditions. The reverberation time (RT), the only parameter used in both countries' regulations to assess acoustic conditions, was found to be higher on both campuses than the RT limits values. Comparison of the measured Speech Transmission Index (STI) and background noise values in the active and inactive ventilation scenario showed a clear variation of the indoor acoustic conditions. The background noise was higher in the active ventilation scenarios (40–57 dBA) than in the inactive ventilation scenarios (34–48 dBA). The average STI values obtained on both campuses for the inactive and active scenarios were 0.54 and 0.51, respectively. In some classrooms an STI difference of 0.1 was found between scenarios. The results obtained in this study provide a broader understanding of the acoustic conditions in university classrooms in Spain and Portugal. The results evidence the need of consider the synergies between the indoor acoustic and air quality conditions to ensure both: the spaces are safe and the acoustic conditions do not interfere with students' learning. The findings show that compliance with the current RT requirements does not ensure that classroom acoustic conditions do not interfere with student performance, and therefore, regulations need to be revised to include additional factors to ensure proper acoustic performance.

Effects of speech intelligibility and work modality on scientific reading productivity in open-plan offices

Speech Transmission Index (STI) is a critical indicator of speech intelligibility in quantitatively evaluating work efficiency in open-plan offices. Previous research has examined the STI-productivity relationship for simple, continuous tasks. Compared to continuous, simple tasks, interleaved complex tasks demand more effort to maintain work efficiency. However, the association of speech intelligibility with the efficiency of complex tasks remains inadequately explored. Therefore, this study investigates the impact of speech intelligibility on the productivity of interleaved scientific reading comprehension, contrasting it with productivity in continuous task modality. Thirty graduate students were recruited and exposed to irrelevant speech environments featuring speech-like pink noise as masking sound. By adjusting the sound pressure levels of speech and masking sounds, seven distinct acoustical conditions with different STI values (0.17, 0.26, 0.36, 0.45, 0.52, 0.57, and Speech_only) were created. A “Quiet” condition was also considered as a control group. Generalized Linear Mixed Models were utilized to analyze the relationships between speech intelligibility, task modality, and objective and subjective outcomes. The study found that, when the STI lies within the range of 0.26–0.45, employees must exert more effort to maintain task efficiency and resist distractions. If task-switching is involved when the STI exceeds 0.50, research efficiency further decreases. Overall, the interruption of tasks appears to amplify the impact of speech intelligibility on research efficiency. These findings underscore the importance of considering both work modality and the acoustic condition in optimizing cognitive performance and the overall user experience.

A modified technique to predict speech privacy and distraction distances in open-plan offices

Open-plan offices have become widely adopted in various industries as a workplace environment. However, this office layout type suffers from speech privacy, which can be represented by the acoustic parameter known as the Speech Transmission Index (STI). ISO 3382-3:2012 provides guidelines for calculating the acoustic parameters of a room tailored explicitly for open-plan offices. However, the existing method in ISO 3382-3:2012 requires a parallel layout of workstations to determine the STI value, which is hardly found in modern office settings. This study presents a technique to predict the ideal values of rP and rD, based on the relationship between %Alcons and the Speech Transmission Index (STI) for a specific workstation, using linear regression and in-situ measurements. The analysis of acoustic conditions in an open-plan office reveals that modified techniques can predict the acoustic quality in a modern office layout. The D2, S values indicate good acoustic quality, but the Lp, A, S,4m values do not meet the required standard. Using %Alcons equations, the study shows how to predict distraction distances and categorize workstations as 'Distracted' or 'Not distracted'. The results indicate only a small percentage of workstations allow for private communication.

Assessment of speech intelligibility during different teaching activities in classrooms with and without acoustic treatment

There is limited data for assessing speech intelligibility in real classrooms with realistic occupied noise levels and teacher’s and students’ speech levels for different teaching activities in Turkish secondary school classrooms. This study investigates the effect of reverberation time (RT), occupied noise levels and signal-to-noise ratio (SNR) on speech transmission index (STI) in real classrooms for instruction and group work. Noise levels were measured and STI values were calculated in two secondary school classrooms with RT of 0.88 s and 2.73 s. During instruction situation, calculated mean STI values were 0.63 (classroom with acoustic treatment) and 0.29 (classroom without acoustic treatment) for normal voice effort and 0.65 (classroom with acoustic treatment) and 0.39 (classroom without acoustic treatment) for raised voice effort. During group work, STI values ranged from 0.50 to 0.74 in classroom with acoustic treatment and from 0.01 to 0.34 in classroom without any acoustic treatment. SNR of 15 dBA is only approached in classroom with acoustic treatment during instruction situation. The effect of increasing SNR on STI is prominent in the classroom without acoustic treatment which already has low SNR values. The present results show that the classroom with acoustic treatment will have good speech intelligibility for instruction with normal vocal effort and for group work with raised vocal effort at 3 m distance. However, the classroom with no acoustic treatment will have STI values in the range of bad and poor intelligibility. The present results confirm the impact of SNR and RT on speech intelligibility and shows that RT value of minimum 0.8 s is optimal to have good speech intelligibility in a secondary school classroom of approximately 250 m3 with a capacity of 18 students.

A prediction model of speech transmission index based on reverberation time in non-native linguistic context

High speech intelligibility is an essential requirement for classrooms, especially in relation to non-native students. Speech transmission index (STI) was proved as the most relevant acoustic parameter to assess speech intelligibility. In this paper, twenty-seven classrooms for non-native teaching purposes were selected for investigation. Physical acoustic measurements were conducted in these classrooms and numerical simulation verification was determined by ODEON version 16. The relationships between STI values and RT values were fitted based on non-linear curve fitting regression models. In this paper, three primary forms of non-linear curve fitting regression models were employed for predicting curves. A logarithmic function was selected as the basic regression equation to describe the effects of RT values on STI values. The results showed that STI values increase with the decrease of RT values for all age groups. From the verified results, it was possible to propose the predictive equation that presents the best accuracy in predicting the experimental data for non-native teaching purposes. The impact of different age groups and linguistic environment on STI were discussed. The prediction model is expected to estimate STI values by using RT values during the early design stage in a non-native linguistic context.

Objective and subjective assessment of the speech intelligibility in rooms with an Active Acoustic Enhancement Systems

Speech Transmission Index (STI), apart from the Reverberation Time (RT), remains an important parameter used for the speech intelligibility assessment indoors. As the Active Acoustic Enhancement Systems (AAES) are getting more and more commonly used, it was verified how such systems affect speech perception. In accordance with the 3382-1 and 3382-2 regulations, objective parameters were measured in two enclosures with the AAES. The RT values varied from 0.91 to 1.61 [s] for the hall in Mińsk Mazowiecki and from 0.75 to 1.52 [s] in Puławy. The STI values varied from 0.57 to 0.64 in Mińsk Mazowiecki and 0.64 to 0.69 in Puławy. Despite the significant differences in the RT values, STI coefficients remained almost unchanged. The listening test was designed to verify if the subjectively assessed intelligibility would confirm the objective measurements' results. 50-element nonsense words (logatome) lists were used for in-situ experiments and, in the second part, binaural laboratory arrangement. Both parts involved over 120 listeners. Three scenes were selected: without AAES and two different AAES setups. In summary, subjective measurements' results were compared with the obtained STI, RT and Clarity (C50, C80) values to prove their importance in indoors speech intelligibility evaluation.

Evaluation of Acoustical Performance for Atrium Design with Respect to Skylight Geometry and Material in the Tropics

Atriums, in most conditions, are considered the heart of buildings, the main spaces where different functions and activities are held. Nowadays, various atrium designs are incorporated in the building, varying from pyramidal to barrel vault. Therefore, it is of great importance to study the basic characteristics of sound fields in such spaces and their related materials. This research aims to determine the effect of various skylight geometry configurations on the atrium’s acoustical performance. Next, an acoustical performance evaluation of the effect of skylight materials was performed by using computer simulation. Four selected atriums with different types of skylight geometries modeling and respective materials, i.e., glass, polycarbonate, and acrylic, have been used in this acoustical simulation. From the results, it can be concluded that an atrium with a pyramidal skylight provides a better reverberation time for music purposes. In contrast, all atriums’ models’ speech transmission index values were almost identical. However, no significant acoustical performance can be found in different used materials. The result also indicates that the shape of the atrium has a higher effect on the acoustical performance than the different materials used.

Experimental Characterization and Acoustic Correction of a Multipurpose Performance Hall: The Italian Theatre “Cavallino Bianco”

This study presents the retrofit acoustic dq1esign of the Italian theatre “Cavallino Bianco”. In its historical configuration, the hall had a curved roof with a pressed-plant fiber ceiling, which was demolished and replaced with a wooden roof without a false ceiling, leading to an increase in volume and a worsening of the reverberation time. This study proposed the realization of a wave ceiling and the application of sound-absorbing and reflecting panels on the walls, which have already been implemented. These modifications have affected the acoustic characterization of the theatre, as shown both through on-site measurements during the main construction phases and through numerical simulations. The reverberation time, clarity index, and speech transmission index (STI) are evaluated considering all the variations in the hall over different construction times, and the optimal solution is identified with regard to different specific uses. The final configuration with the new roof, by reducing the volume of the hall and using sound-absorbing materials, significantly reduces the reverberation time (e.g., at 2000 Hz, this reduction is from 2.33 to 1.47). In addition, the hall at full capacity with chairs and people shows evident improvement in terms of the clarity index, allowing the theatre to be used for a wide range of musical genres such as instrumental, symphonic, and opera performances. As regards the Combos 00 (concrete roof without vertical sound acoustic panels) and 01-a/b/c (wooden roof with draped curtains), the STI values are never lower than 0.42 and never higher than 0.70; therefore, the room never experiences poor or excellent conditions at any point. The Combos 01-a and 01-b, which have a non-performing C80, have a good STI index, confirming the difficulty of achieving a configuration that can be optimal a variety of uses. Combo 01 (wooden roof without vertical sound acoustic panels and no draped curtains), which has a good C80 value, presents a lower STI value, with an average performance. The STI values of Combo 02-a (characterized by wave false ceiling and vertical sound acoustic panels) are never lower than 0.52 and never higher than 0.60; therefore, neither poor nor excellent conditions are experienced in the room, but there is still a slight improvement over the combos 00 and 01.

Acoustical treatment characterization of a classroom with wood-based composites

The built environment might be acoustically treated in different ways in terms of complexity and cost. This research proposes an alternative for the acoustical treatment of an existing classroom through the insertion of wooden composites (i.e. panels) which were attached on the walls. This proposition sought to demonstrate an alternative that was easy in the context of implementation and feasible from the perspective of sustainability and cost. Industrialized wood composites from the south part of Brazil were chosen, such as the MDF (Medium Density Fiberboard), the OSB (Oriented Strand Board) and the WWCB (Wood-Wool Cement Board) with different thicknesses. In a acoustically treated classroom, the reverberation time (T20) and the Speech Transmission Index (STI) were evaluated as objective parameters. Three-dimensional models were built and validated with measurements using an open source software (I-SIMPA) in order to identify which scheme could provide the optimal T20. In order to complement the analysis, subjective tests were carried out with a sample of men and women to determine the Word Discrimination Testing (WDT) applied to the classroom environment. WWCB-type panels increased the STI values at different seats over the classroom and the analysis of the Sound Pressure Levels (SPL) distribution along the seats led to the conclusion that there was no excessive absorption of high-frequency energy. Finally, the subjective tests proved that the WWCB type (50.0 mm thick) improved the speech intelligibility.

The speech intelligibility and applicability of the speech transmission index in large spaces

This paper aims to explore the influence factors of speech intelligibility and the applicability of the speech transmission index (STI) in large spaces, where the sound energy is unevenly distributed and non-exponentially decays. The subjective speech intelligibility tests were conducted in Mandarin (China mainland) in two large spaces with volumes of 97,000 m3 and 246,000 m3. Objective indicators such as the Reverberation Time (RT), Early Decay Time (EDT), Definition (D50), and Speech Transmission Index (STI) under different signal-to-noise ratio (SNRs) were also measured in these two spaces. The results showed that both the SNR and room acoustics had significant effect on the speech intelligibility in these two spaces, but the effect of room acoustics on speech intelligibility was also affected by SNR. The speech intelligibility scores significantly increased with the increase in SNR when the SNR was less than 14.4 dB. In terms of room acoustics, D50 was more relevant to speech intelligibility than RT and EDT in these two large spaces when SNR ranged from −5dB to 15 dB. The STI value in large spaces should not be used as in ordinary spaces to evaluate the speech intelligibility. Based on the tests in this paper, the corresponding relation between STI and speech intelligibility in large spaces was modified, and a new rating threshold of STI was also proposed according to the revised relation, which indicated a necessity to modify the rating criteria of using STI to predict speech intelligibility in large spaces.

Irrelevant speech effect in open plan offices: Comparison of two models explaining the decrease in performance by speech intelligibility and attempt to reduce interindividual differences of the mental workload by task customisation

For employees working in open plan offices, speech noise is now recognised as the main source of disturbance. In the literature, a series of studies on open spaces have found that the increased speech intelligibility happens to decrease the performance during a short-term memory task. The theoretical model proposed by Hongisto relates the decreased performance (DP) to the Speech Transmission Index (STI). The model predicts that for STI values from 0.7 to 1, which correspond to a speech signal with an intelligibility of almost 100%, the DP remains constant at 7%, but few studies have examined the high end of this range. Here, we investigated the relationship between the DP and the STI by varying the STI up to 0.9. Fifty-five subjects between 25- and 59-years-of-age participated in the experiment. Subjects performed a short-term memory task in silence and in four different sound conditions (STI from 0.25 to 0.9). The task itself was personalised by prior measurement of mnemonic span. It was thus possible to define two different cognitive loads (low/high) based on the mnemonic span value determined for each subject. Subjects subjectively assessed the mental workload and sound annoyance at the end of each short-term memory task in each sound condition. Significant interactions between STI and DP, mental workload and sound annoyance were found. In addition, the age of subjects correlated significantly with their performance during the short-term memory task.

Assessing the Effect of Dome Shape and Location on The Acoustical Performance of a Mosque by Using Computer Simulation

Architecturally, the dome is one evolutionary presence in most mosques of modern day. Besides mihrab, the dome is one of the architectural elements that has a phenomenon of concentration of energy by reflected sound waves from concave surfaces. The aim of this research is to compare the acoustical performance of different shapes of the dome and their respective locations by using geometrical approach computer simulation. Four types of dome that are commonly used on a mosque; Arabic, segmental, hemispherical, and onion, were modeled to compare their acoustical parameters i.e. reverberation time (RT) and speech transmission index (STI). It can be concluded that the shape of the dome does affect the RT. Furthermore, the shape of the dome also affects the STI - the larger the volume, the lower the STI value. However, the locations of a dome has little significance over acoustical parameter. The findings of this research may not limit to mosques only, but to any similar building that has similar typology.

A new verification of the speech transmission index for the English language

The speech transmission index (STI) is one of the most widely used and standardized methods for objective prediction of speech intelligibility of transmission channels. The original verification of the relationship between the STI and the intelligibility for the English language was published in 1987. The methodology employed then for the listening tests and the different input spectrum recommended today by the current STI method suggest that the relationship STI vs. speech intelligibility needs to be verified for the English language. This paper presents a new verification of the current STI for the English language with binaural listening and the speech materials presented to the listeners in a real room from a real sound source. Two hundred and ten subjects participated in speech intelligibility tests designed to replicate real-life listening conditions. The speech materials were contaminated with natural reverberation, noise, band pass limiting and echoes, and the listeners were not familiarized with the speech materials before the tests, in order to better replicate everyday situations. Results showed lower intelligibility scores than the earlier verification presented in Annex E of the current STI standard (IEC60268–16:2011) for most of the scenarios that were investigated. The correlation between STI and speech intelligibility was also investigated for the English language with a newly proposed male speech spectrum. The accuracy of STI intelligibility prediction with the new male spectrum was found higher than that attained with the current IEC specified male spectrum. These new findings give new and additional insights into the interpretation of intelligibility using the STI values.

Fast estimation of Speech Transmission Index using the Reverberation Time: Comparison between predictive equations for educational rooms of different sizes

Ensuring a high speech intelligibility is an essential issue for educational rooms, especially in relation to the effectiveness of the student learning process. The Reverberation Time and the Speech Transmission Index are objective parameters commonly used to assess the acoustic quality of the rooms, according to their intended use. Especially the Speech Transmission Index can give interesting information about the speech intelligibility. As with the Reverberation Time, it would be very important to have simple equations aimed to the prediction of Speech Transmission Index values during the early design stage. There are different studies in the literature that propose equations, obtained on empirical basis, for a fast estimation of the Speech Transmission Index as a function of the Reverberation Time. In this paper, a comparison of the most significant equations proposed in the literature was done using the Reverberation Time and Speech Transmission Index values obtained from a measurement campaign at the School of Engineering of the University of Pisa on a sample of 11 educational rooms. The analysis was carried out for educational rooms of different sizes, in order to highlight differences in the prediction accuracy depending on the volume of the rooms. From the analysis results it was possible to highlight the equation that shows the best accuracy in predicting the experimental data for the sample of investigated rooms and propose, through a regression analysis, two new equations for the rapid estimation of the Speech Transmission Index.

An investigation of speech intelligibility for second language students in classrooms

In this paper, speech intelligibility in 9 classrooms of a middle school and 11 classrooms of a university in Hong Kong was investigated. The subjective speech intelligibility tests were conducted with students aged from 12 to 21 in these classrooms. Besides, objective acoustical measurements were performed in each listening position and testing conditions in each classroom. The relationship between subjective speech intelligibility scores and speech transmission index (STI) was discussed based on regression models. The effects of different age groups on the speech intelligibility were compared. The results show that speech intelligibility scores increase with STI value for all age groups. The speech intelligibility scores increase as the age increases under the same STI condition. The differences between age groups are decreased with the increase of STI values. English speech intelligibility scores in Hong Kong are always lower compared with native language researches under the same values of STI. Better STI values and better acoustical environment are needed because English is not the native language for students in Hong Kong but the official educational language.

Logatome and Sentence Recognition Related to Acoustic Parameters of Enclosures

AbstractThe paper deals with relationship between speech recognition and objective parameters of enclosures. Six enclosures were chosen: a church, an assembly hall of a music school, two courtrooms of different volumes, a typical auditorium and a university concert hall. Dirac 4.1 software was used to record impulse responses (IRs) in the chosen measurement points of each enclosure. On this base, the following objective parameters of the enclosure were determined: Reverberation Time (RT), Early Decay Time (EDT), Weighted Clarity (C50) and Speech Transmission Index (STI). A convolution of the IRs with logatome tests and the Polish Sentence Test (PST) was made. Logatome recognition and speech reception threshold (SRT - i.e., SNR yielding 50% speech recognition) were evaluated and their dependence on the objective parameters were determined. Generally a linear relationship between logatome or SRT and RT or EDT was found. However, speech recognition was nonlinearly related (according to psychometric function) to STI values. The most sensitive range of the logatome and sentence recognition relative to STI changes corresponded to the middle range of STI values. Below and above this range, logatome and sentence recognition were much less dependent of STI changes.

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.

An Experimental Study of Acoustic Comfort in Open Space Banks Based on Speech Intelligibility and Noise Annoyance Measures

Abstract Tasks requiring intensive concentration are more vulnerable to noise than routine tasks. Due to the high mental workload of bank employees, this study aimed to evaluate acoustic comfort in open-space banks based on speech intelligibility and noise annoyance metrics. Acoustic metrics including preferred noise criterion (PNC), speech transmission index (STI), and signal to noise ratio (SNR) were measured in seventeen banks (located in Hamadan, a western province of Iran). For subjective noise annoyance assessments, 100-point noise annoyance scales were completed by bank employees during activities. Based on STI (0.56±0.09) and SNR (20.5±8.2 dB) values, it was found that speech intelligibilities in the workstations of banks were higher than the satisfactory level. However, PNC values in bank spaces were 48.2±5.5 dB, which is higher than the recommended limit value for public spaces. In this regard, 95% of the employees are annoyed by background noise levels. The results show irrelevant speech is the main source of subjective noise annoyance among employees. Loss of concentration is the main consequence of background noise levels for employees. The results confirmed that acoustic properties of bank spaces provide enough speech intelligibility, while staff’s noise annoyance is not acceptable. It can be concluded that due to proximity of workstations in open-space banks, access to very short distraction distance is necessary. Therefore, increasing speech privacy can be prioritised to speech intelligibility. It is recommended that current desk screens are redesigned in order to reduce irrelevant speech between nearby workstations. Staff’s training about acoustic comfort can also manage irrelevant speech characteristics during work time.

Model of Thailand Speech Intelligibility (T-SI) in the Large Classrooms from Public University

The objectives of this research are to evaluate acoustic environments and to forecast STI values from spatial component variables in the large classrooms of the Thai public university that were specially controlled the same room finishing materials including the floor, walls, and ceiling. Whereas the five spatial component factors included (1) Room Volume (RV), (2) Ceiling Height (CH), (3) the Ratio of Depth to Width (Rdw), (4) Total Room Surface (TS), and (5) Percentage of Absorbing Surface areas (PAS). The research tools were the smartphones that used the applications for acoustical evaluation and speech intelligibility analysis. The Speech Transmission Index (STI), Reverberation Time (RT), and Background Noise Level (BNL) were collected by the calibrated microphone in the nine points distributed across the entire room. And also, the sounds for testing were simulated such as balloon burst, and STIPA signal via a sound generator. The Thailand Speech Intelligibility (T-SI) model was developed by the multiple regression analysis with a statistical at a confidence level of 95%.The results showed that this T-SI model depended on the strongly positive relationship of PAS and the slightly positive relationship of CH, TS while the RV, Rdw were slightly the negative relationship and which predicted STI values. Moreover, the highest affecting variable of T-SI model was CH and the lowest was PAS. However, this research implies that the improving room acoustic quality would be adjusting the sound absorbing surface areas i.e., increase the cloth curtain or appropriate methods.