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This paper investigates the interrelation of room acoustics parameters as measured in lecture theatres/classrooms using four sound source configurations. Ten typical rooms were selected as representative of university premises and measured to ISO 3382 standards. The study focuses initially on the type of sound source used, to establish the suitabil...
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Context 1
... performance. The conditions present in a space during a measuring session will thus unavoidably affect the output in different ways for different measures. As such, care needs to be taken when comparing dissimilar parameters or making an assumptive assessment, based on a particular methodology. STI comprises a measure describing speech intelligibility using a single number for seven octave bands, subsequently corresponding to more than a single Clarity value. In order to enable a comparison in octave band level detail, the modulation transfer index (MTI) is considered as the equivalent octave band ‘STI’, nonetheless the benefit of octave band weighting and redundancy corrections is not considered and therefore results could underestimate the potential relationship. In utilizing the relation between the C x energy ratios and STI it should be reminded that the former does not account for the influence of background noise. Thus, the particular interrelation is subject to change in every environment, depending on the noise character. It is worth noting that while U x is a measure that can be used as an alternative to C x (in order to account for S/N), clarity is commonly used to quantify general acoustic quality in rooms. For this reason, its design and specific purpose is often overlooked, with comparisons likely to take place without regard to any limitations. A comparison of fundamentally different measures on this basis can be constructively utilized to discern the acoustic conditions. Figure 1 shows the relation of C 50 and C 80 to MTI for two conditions, with and without background noise. For noiseless conditions the relation of the two measures was approximately linear, agreeing with earlier results by Bradley [1], while C 80 appeared to be better related to MTI. The associated correlation coefficients were nonetheless comparable with values of 0.91 and 0.96, respectively for the pairs C 50 -MTI and C 80 -MTI, see figure 1 (I-II) , with analogous performance for all four source configurations. In the conditions accounting for background noise the particular associations break down, as the measures compared are effectively modified into two fundamentally different measures. Considering that the particular relation, see figure 1 (III-IV) could be altered even within the same room under different noise conditions, a comparison of C to STI when accounting for background noise would appear as of minor significance unless some level of consistency in the noise character can be achieved. When the S/N is high enough to render the effect of BGNL negligible in a practical application, it would be possible to predict the speech intelligibility in terms of STI from the C 50 or C 80 datasets with a high level of accuracy, see [2]. Therefore, for a high signal level condition C x might also be used as a direct descriptor of speech intelligibility. This relationship would be invalidated to a large extent when considering marginal conditions and thus could be used, if established, to ascertain BGNL as a significant factor in the acoustical conditions. The relation of room reverberance to STI followed a similar trend as regards the effect of background noise. Considering EDT and T 30 , an evident relation of reverberance to the MTI was found for noiseless (or adequate S/N) conditions, see figure 2, ...
Context 2
... performance. The conditions present in a space during a measuring session will thus unavoidably affect the output in different ways for different measures. As such, care needs to be taken when comparing dissimilar parameters or making an assumptive assessment, based on a particular methodology. STI comprises a measure describing speech intelligibility using a single number for seven octave bands, subsequently corresponding to more than a single Clarity value. In order to enable a comparison in octave band level detail, the modulation transfer index (MTI) is considered as the equivalent octave band ‘STI’, nonetheless the benefit of octave band weighting and redundancy corrections is not considered and therefore results could underestimate the potential relationship. In utilizing the relation between the C x energy ratios and STI it should be reminded that the former does not account for the influence of background noise. Thus, the particular interrelation is subject to change in every environment, depending on the noise character. It is worth noting that while U x is a measure that can be used as an alternative to C x (in order to account for S/N), clarity is commonly used to quantify general acoustic quality in rooms. For this reason, its design and specific purpose is often overlooked, with comparisons likely to take place without regard to any limitations. A comparison of fundamentally different measures on this basis can be constructively utilized to discern the acoustic conditions. Figure 1 shows the relation of C 50 and C 80 to MTI for two conditions, with and without background noise. For noiseless conditions the relation of the two measures was approximately linear, agreeing with earlier results by Bradley [1], while C 80 appeared to be better related to MTI. The associated correlation coefficients were nonetheless comparable with values of 0.91 and 0.96, respectively for the pairs C 50 -MTI and C 80 -MTI, see figure 1 (I-II) , with analogous performance for all four source configurations. In the conditions accounting for background noise the particular associations break down, as the measures compared are effectively modified into two fundamentally different measures. Considering that the particular relation, see figure 1 (III-IV) could be altered even within the same room under different noise conditions, a comparison of C to STI when accounting for background noise would appear as of minor significance unless some level of consistency in the noise character can be achieved. When the S/N is high enough to render the effect of BGNL negligible in a practical application, it would be possible to predict the speech intelligibility in terms of STI from the C 50 or C 80 datasets with a high level of accuracy, see [2]. Therefore, for a high signal level condition C x might also be used as a direct descriptor of speech intelligibility. This relationship would be invalidated to a large extent when considering marginal conditions and thus could be used, if established, to ascertain BGNL as a significant factor in the acoustical conditions. The relation of room reverberance to STI followed a similar trend as regards the effect of background noise. Considering EDT and T 30 , an evident relation of reverberance to the MTI was found for noiseless (or adequate S/N) conditions, see figure 2, ...
Context 3
... performance. The conditions present in a space during a measuring session will thus unavoidably affect the output in different ways for different measures. As such, care needs to be taken when comparing dissimilar parameters or making an assumptive assessment, based on a particular methodology. STI comprises a measure describing speech intelligibility using a single number for seven octave bands, subsequently corresponding to more than a single Clarity value. In order to enable a comparison in octave band level detail, the modulation transfer index (MTI) is considered as the equivalent octave band ‘STI’, nonetheless the benefit of octave band weighting and redundancy corrections is not considered and therefore results could underestimate the potential relationship. In utilizing the relation between the C x energy ratios and STI it should be reminded that the former does not account for the influence of background noise. Thus, the particular interrelation is subject to change in every environment, depending on the noise character. It is worth noting that while U x is a measure that can be used as an alternative to C x (in order to account for S/N), clarity is commonly used to quantify general acoustic quality in rooms. For this reason, its design and specific purpose is often overlooked, with comparisons likely to take place without regard to any limitations. A comparison of fundamentally different measures on this basis can be constructively utilized to discern the acoustic conditions. Figure 1 shows the relation of C 50 and C 80 to MTI for two conditions, with and without background noise. For noiseless conditions the relation of the two measures was approximately linear, agreeing with earlier results by Bradley [1], while C 80 appeared to be better related to MTI. The associated correlation coefficients were nonetheless comparable with values of 0.91 and 0.96, respectively for the pairs C 50 -MTI and C 80 -MTI, see figure 1 (I-II) , with analogous performance for all four source configurations. In the conditions accounting for background noise the particular associations break down, as the measures compared are effectively modified into two fundamentally different measures. Considering that the particular relation, see figure 1 (III-IV) could be altered even within the same room under different noise conditions, a comparison of C to STI when accounting for background noise would appear as of minor significance unless some level of consistency in the noise character can be achieved. When the S/N is high enough to render the effect of BGNL negligible in a practical application, it would be possible to predict the speech intelligibility in terms of STI from the C 50 or C 80 datasets with a high level of accuracy, see [2]. Therefore, for a high signal level condition C x might also be used as a direct descriptor of speech intelligibility. This relationship would be invalidated to a large extent when considering marginal conditions and thus could be used, if established, to ascertain BGNL as a significant factor in the acoustical conditions. The relation of room reverberance to STI followed a similar trend as regards the effect of background noise. Considering EDT and T 30 , an evident relation of reverberance to the MTI was found for noiseless (or adequate S/N) conditions, see figure 2, ...
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Citations
... However, the size of university classrooms can also vary significantly. It was proposed in [5] and [6] to divide the university classrooms into three classes: small, medium and large. In [6], small, medium and large rooms include rooms less than 230 m 3 , 230-350 m 3 , and more than 350 m 3 , respectively. ...
... It was proposed in [5] and [6] to divide the university classrooms into three classes: small, medium and large. In [6], small, medium and large rooms include rooms less than 230 m 3 , 230-350 m 3 , and more than 350 m 3 , respectively. ...
In this paper, correlation coefficients between the five objective estimates of speech quality, on the one hand, and the Speech Transmission Index as speech intelligibility measure, on the other hand, were estimated. This comparison was performed using binaural room impulse responses corresponded to different points of the three university auditoriums of different sizes. Speech quality was assessed using intrusive speech quality measures: Segmental Signal-toNoise Ratio, Logarithmic Spectral Distortion, Frequency Weighted Segmental Signal-to-Noise Ratio, Bark Spectral Distortion, and Perceptual Evaluation of Speech Quality. The formation of signals distorted by reverberation was performed by convolving of pure signals with binaural room impulse responses of the premises. A high level of correlation (0.6-0.99) of Bark Spectral Distortion estimates with estimates of the Speech Transmission Index for rooms of different sizes was revealed. Correlation of estimates (0.65-0.98) of Frequency Weighted Segmental Signal-to-Noise ratio with Speech Transmission Index estimates was observed for medium and large rooms. Significant correlation (0.96-0.99) of Perceptual Evaluation of Speech Quality with Speech Transmission Index estimates was observed only for large audiences. At the same time, estimates of the Segmental Signal-to-Noise Ratio and Logarithmic Spectral Distortion turned out to be practically uncorrelated with Speech Transmission Index estimates for all studied premises.
... There are various proposals for the classification of university classrooms by size. For example, in [19] it is proposed to consider small rooms with a volume of less than 230 m 3 , medium-sized rooms include those with a volume of 230-350 m 3 , and large rooms with a volume of more than 350 m 3 . ...
In this paper, five objective measures of the quality of speech signals distorted by reverberation are compared with the Speech Transmission Index (STI). The main aim of the comparison is to further test and explain the reasons for the previously discovered phenomenon of an increase in the speech quality and intelligibility with increasing room size. The comparison was performed for three university classrooms of small, medium and large sizes. The correlation coefficients between the quality and intelligibility estimates of speech obtained for 5-6 points of each room were estimated. Speech signal quality was assessed using intrusive measures such as segmental signal-to-noise ratio (SSNR), log-spectral distortion (LSD), frequency-weighted segmental signal-to-noise ratio (FWSNR), bark spectral distortion (BSD), and perceptual evaluation of speech quality (PESQ). For BSD, high correlation coefficients (0.57-0.99) were obtained for rooms of all sizes and there was revealed an increase in the correlation coefficient with the room size increase, which can be explained by a decrease in the density of early sound reflections. For FWSNR, high correlation (0.65-0.98) was obtained for medium and large rooms. For PESQ, high correlation (0.96-0.99) was obtained for large classroom. SSNR and LSD were found to be uncorrelated with STI for rooms of all sizes.
... According to this classification, there are small, medium and large size premises, with a volume of less than 350 m3, 350-650 m3 and more than 650 m3, respectively. In [7], small, medium and large classrooms include premises with a volume of less than 230 m3, 230-350 m3 and more than 350 m3, respectively. ...
Estimates of speech quality and intelligibility for three university classrooms of small, medium and large sizes are presented. The quality and intelligibility of speech were assessed by objective methods using binaural room impulse responses, measured at 5-6 points of the premises. The measures of speech quality were log-spectral distortion (LSD), bark spectral distortion (BSD) and perceptual evaluation of speech quality (PESQ), and the objective measure of speech intelligibility was the speech transmission index (STI). Among the quality measures considered, only BSD is shown to be highly correlated with STI measures for all three classrooms. In this case, correlation coefficient R varies from minus 0.6 for a small room to minus 0.98 for a large room. The close relationship between PESQ and STI is observed only in the case of a large classroom (R = 0.96-0.99), and the LSD measure was found to be uncorrelated with STI for premises of all sizes. The obtained results can serve as a justification for the use of BSD instead of STI, and vice versa, in the acoustic examination of classrooms of different sizes. *Corresponding Author
... In this case, three classes of premises of small, medium-sized, and large size with the volume of less than 350 m 3 , 350-650 m 3, and more than 650 m 3 , respectively, were separated. A similar classification of premises was proposed in [21] where small, medium-sized and large lecture rooms included the premises of less than 230 m 3 , 230-350 m 3, and more than 350 m 3 , respectively. A typical feature of large lecture rooms, as well as concert halls, is the sloping floor [19,20]. ...
The scores of speech intelligibility, obtained using objective and subjective methods for three university lecture rooms of the small, medium, and large sizes with different degrees of filling, were presented. The problem of achieving high speech intelligibility is relevant for both students and university administration, and for architects designing or reconstructing lecture rooms. Speech intelligibility was assessed using binaural room impulse responses which applied an artificial head and non-professional quality audio equipment for measuring. The Speech Transmission Index was an objective measure of speech intelligibility, while the subjective evaluation of speech intelligibility was carried out using the articulation method.
Comparative analysis of the effectiveness of parameters of impulse response as a measure of speech intelligibility showed that Early Decay Time exceeded the score of the T30 reverberation time but was ineffective in a small lecture room. The C50 clarity index for all the considered lecture rooms was the most informative. Several patterns determined by the influence of early sound reflections on speech intelligibility were detected. Specifically, it was shown that an increase in the ratio of the energy of early reflections to the energy of direct sound leads to a decrease in speech intelligibility. The exceptions are small, up to 30?40 cm, distances from the back wall of the room, where speech intelligibility is usually slightly higher than in the middle of the room. At a distance of 0.7–1.7 m from the side walls of the room, speech intelligibility is usually worse for the ear, which is closer to the wall. The usefulness of the obtained results lies in refining the quantitative characteristics of the influence of early reflections of sound on speech intelligibility at different points of lecture rooms.
... The STI is a common objective parameter used to assess speech intelligibility [8][9][10] not only in classrooms but also in conference halls, theatres, public address [11][12][13]. While the RT can be reasonably estimated with simple equations, even during the early design stage of a building, the STI generally requires more complex evaluations or in situ measurements which are difficult or impossible to achieve during the early design stage [15][16][17][18]. ...
... Similarly to previous studies [18], the rooms were divided into three groups: small (S) with volumes lower than 350 m 3 , medium (M) with volumes in the range of 350-650 m 3 , and large (L) with volumes higher than 650 m 3 . All the rooms have rectangular shapes, but they are characterized by different use and different floor types: in the sample, each room is indicated as teaching (TR) or drawing (DR) room with flat or stepped floor. ...
Today, millions of standardized English as a foreign language proficiency tests are administered globally each year. A large portion of this is conducted as a paper-based test in which the listening section is commonly delivered through loudspeakers to groups of test takers, a method in which the audio signals are exposed to the acoustic tendencies of each particular venue. As it is well-established in the literature that non-native listeners are more susceptible to adverse listening conditions compared to their native counterparts, there is a need for an objective examination of the acoustic quality of such environments. This study examined the speech transmission index for public address systems (STIPA) for three types of sound sources (wall-mounted speakers, radio cassette player, and amplified speaker) and reverberation time (RT) in 10 unoccupied classrooms commonly used as test rooms at a university in Japan. The results revealed that STI was found to be statistically significantly different for the amplified speaker compared to both or one other sound source in eight out of 10 rooms. The amplified speaker also recorded the highest STI among the three sound sources in eight out of 10 rooms and the most rooms with STI entirely above 0.66, a minimum target value prescribed in IEC 60268–16:2020 as exhibiting high speech intelligibility. Additionally, ≥ 0.66 STI was consistently observed in rooms with RT0.5-2kHz ≤ 0.7 s. Further observations are discussed to better understand the current conditions under which these tests are administered
