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Optimizing Classroom Acoustics Using Computer Model Studies
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Speech intelligibility in rooms is determined by both room acoustics characteristics as well as speech-to-noise ratios. These two types of effects are combined in measures such as useful-to-detrimental sound ratios which are directly related to speech intelligibility. This paper reports investigations of optimum acoustical conditions for classrooms using the ODEON room acoustics computer model. By determining conditions that relate to maximum useful-to-detrimental sound ratios, optimum conditions for speech are determined. The results show that an optimum mid-frequency reverberation time for a classroom is approximately 0.5 s, but speech intelligibility is not very sensitive to small deviations from this optimum. Speech intelligibility is influenced more strongly by ambient noise levels. The optimum location of sound absorbing material was found to be on the upper parts of the walls.
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... These windows directly overlook a crowded, noisy street, parking areas and buildings 2 and 7 (see Figure 1). The main architectural features of both auditoria are summarised in Tables 1 and 2. Speech intelligibility (SI) in lecture rooms is a major concern in educational spaces not only to support the learning process (Reich and Bradley, 1998) but also for lecturers' comfort. Recent studies indicate that improper acoustic conditions in lecture rooms cause severe vocal problems for approximately one-tenth of teachers (Brunskog et al., 2009). ...
... Recent studies indicate that improper acoustic conditions in lecture rooms cause severe vocal problems for approximately one-tenth of teachers (Brunskog et al., 2009). Speech intelligibility is a single measure for both room acoustics and the speech-to-noise ratio (S/N) (Reich and Bradley, 1998); it can be governed by different indicators, such as the useful to detrimental sound ratio (U 80 ), speech transmission index (STI) or its common variant, the rapid speech transmission index (RASTI) (Reich and Bradley, 1998;Shams and Rama krishnan, 2012). SI is considered to be a function of reverberation time (T); early reflection energy can increase the S/N by up to 9 dB (Bradley and Sato, 2003), while an S/N of + 15 dB can raise SI scores by up to 100% (Bradley, 2002). ...
... Recent studies indicate that improper acoustic conditions in lecture rooms cause severe vocal problems for approximately one-tenth of teachers (Brunskog et al., 2009). Speech intelligibility is a single measure for both room acoustics and the speech-to-noise ratio (S/N) (Reich and Bradley, 1998); it can be governed by different indicators, such as the useful to detrimental sound ratio (U 80 ), speech transmission index (STI) or its common variant, the rapid speech transmission index (RASTI) (Reich and Bradley, 1998;Shams and Rama krishnan, 2012). SI is considered to be a function of reverberation time (T); early reflection energy can increase the S/N by up to 9 dB (Bradley and Sato, 2003), while an S/N of + 15 dB can raise SI scores by up to 100% (Bradley, 2002). ...
Based on the commonly used indicators for speech intelligibility, this work acoustically evaluates the two largest auditoria in the Faculty of Engineering, Helwan University, Cairo, Egypt, using experimental and digital simulation techniques. Design treatments were also suggested to improve the acoustic performance of the auditoria, where the impact of these treatments was checked using the simulation as well. The models that were analysed using the CATT software were first validated utilizing the results of the field work in the unoccupied rooms. The results showed that the acoustic quality of the two auditoria are far from the optimal conditions due to their improper acoustic characteristics and the high noise levels as well. The results of improvement proposals showed that altering the ceiling shape and adding efficient absorptive materials to the rear surfaces successfully reduced the excessive reverberation time to the optimal values, increased the early reflections and eliminated the shadow zones. In addition, decreasing the noise levels by 20 dB due to improving the window insulation noticeably improved the speech intelligibility at all receivers.
... INTRODUCTION Acoustic performance of lecture auditoria has attracted many researchers for its direct impact on the learning process in addition to the impact on the convenience of recipients and lecturers themselves [1]. Inadequate acoustic performance of any auditorium results from either room acoustics or signal to noise ratio that decrease because of high ambient noise or low early reflections energy [2]. There are a number of acoustic indicators that are used to assess the performance of any auditoria, particularly, occupied reverberation time (T o ), speech transmission index (STI) or useful to detrimental sound ratio (U 80 ) as a function of T [3], and ambient noise level (L eq ), because of its impact on the comfort of the recipients and also to avoid the sound problems that may affect the lecturers themselves, as indicated by some studies [1]. ...
... There are a number of acoustic indicators that are used to assess the performance of any auditoria, particularly, occupied reverberation time (T o ), speech transmission index (STI) or useful to detrimental sound ratio (U 80 ) as a function of T [3], and ambient noise level (L eq ), because of its impact on the comfort of the recipients and also to avoid the sound problems that may affect the lecturers themselves, as indicated by some studies [1]. Speech intelligibility can be governed by many factors such as; speech transmission index (STI) ) [2] [4], optimum reverberation time (T Opt ) [4], ambient noise level (L eq ) which should not exceed 35 dB to avoid distraction in learning facilities [3] [5]. ...
... Therefore, concerning sustainability aspects, they can be made of any green material, reducing the environmental footprint of the whole process. The acoustic simulation of a wide application in a 3D virtual enclosure is a useful tool in a preliminary step in the assessment of their performance [44][45][46]. ...
... The 3D model was modeled using a small group of different materials (see Table 5) to reduce the uncertainties underlying the assignment of material properties to each surface. With regard to the absorption area distribution, it should be noted that, generally, the seats are the most sound absorbing objects in a lecture hall in unoccupied state [23,[44][45][46]. The remaining layers of the model (walls, floor, ceiling) are made up of rather hard and reflective surfaces, and thus they show low values in the whole frequency range. ...
Sound absorbing micro-perforated panels (MPPs) are being increasingly used because of their high quality in terms of hygiene, sustainability and durability. The present work investigates the feasibility and the performance of MPPs when used as an acoustic treatment in lecture rooms. With this purpose, three different micro-perforated steel specimens were first designed following existing predictive models and then physically manufactured through 3D additive metal printing. The specimens’ acoustic behavior was analyzed with experimental measurements in single-layer and double-layer configurations. Then, the investigation was focused on the application of double-layer MPPs to the ceiling of an existing university lecture hall to enhance speech intelligibility. Numerical simulations were carried out using a full-spectrum wave-based method: a finite-difference time-domain (FDTD) code was chosen to better handle time-dependent signals as the verbal communication. The present work proposes a workflow to explore the suitability of a specific material to speech requirements. The measured specific impedance complex values allowed to derive the input data referred to MPPs in FDTD simulations. The outcomes of the process show the influence of the acoustic treatment in terms of reverberation time (T30) and sound clarity (C50). A systematic comparison with a standard geometrical acoustic (GA) technique is reported as well.
... Acoustic performance of lecture auditoria has attracted many researchers for its direct impact on the learning process in addition to the impact on the convenience of recipients and lecturers themselves [1]. Inadequate acoustic performance of any auditorium results from either room acoustics or signal to noise ratio that decrease because of high ambient noise or low early reflections energy [2]. There are a number of acoustic indicators that are used to assess the performance of any auditoria, particularly, occupied reverberation time (T o ), speech transmission index (STI) or useful to detrimental sound ratio (U 80 ) as a function of T [3], and ambient noise level (L eq ), because of its impact on the comfort of the recipients and also to avoid the sound problems that may affect the lecturers themselves, as indicated by some studies [1]. ...
... There are a number of acoustic indicators that are used to assess the performance of any auditoria, particularly, occupied reverberation time (T o ), speech transmission index (STI) or useful to detrimental sound ratio (U 80 ) as a function of T [3], and ambient noise level (L eq ), because of its impact on the comfort of the recipients and also to avoid the sound problems that may affect the lecturers themselves, as indicated by some studies [1]. Speech intelligibility can be governed by many factors such as; speech transmission index (STI) ) [2] [4], optimum reverberation time (T Opt ) [4], ambient noise level (L eq ) which should not exceed 35 dB to avoid distraction in learning facilities [3] [5]. ...
... Speech intelligibility in an enclosure is influenced by many parameters reasonably well accountable in terms of objective descriptors. Among these parameters, the most significant are the signal-to-noise ratio (S/N) that represents the emergence of speech level over the background noise (Reich and Bradley, 1998) and the reverberation time (RT) which suffers reduction as a result of additional sound absorption brought by the audience (Doelle, 1972). ...
... To find a theoretical basis for calculating reverberation time, many researchers contributed new theories. Since Sabine published his results, several different approaches have been adopted to obtain equations that describe the reverberation characteristics (Franklin, 1903;Eyring, 1930;Millington, 1932;Sette, 1933;Fitzroy, 1959;Kosten, 1965;Tohyama and Suzuki, 1995;Arau-Purchades,1988;Bistafa and Bradley, 2000). However, the general description of the reverberation time based on Sabine's reverberation theory is still in common use and is used in this work. ...
The audience constitutes the major sound absorbent materials in most church auditoria and, non-inclusion of the sound absorbed by the audience in the determination of the optimum reverberation time from the design stage accounts for the problem of poor sound quality in such church auditoria. To address this problem, this research was carried out to provide designers with data on sound absorption by an individual at some octave band frequencies important for understanding speech. The work utilized the Sabine's formula for Reverberation Time to determine the sound absorption per person at Octave band frequencies of 125Hz, 250Hz, 500Hz, 1000Hz, 2000Hz and 4000Hz. Data which included the volume, sitting capacity of persons and reverberation time of eight (8) churches were obtained when the churches were occupied and when unoccupied. These data gave the calculated average sound absorption per person of 0.29, 0.43, 0.51, 0.68, 0.71 and 0.73 at these octave band frequencies respectively, all showing that the average sound absorption by an individual increases with frequency within this octave band frequency range.
... Different predictive models have been proposed to grant the best acoustic conditions in this kind of rooms (Fratoni et al. (2019), Choi (2017)). Ray-tracing simulation methods were usually em-ployed during these works (Astolfi et al. (2008), Reich and Bradley (1998), Hodgson and Wong (2009), Bistafa and Bradley (2000)). ...
... Parametreler içerisinde önemli bir yer tutan ve diğer parametreleri etkileyen reverberasyon süresinin uygun değerlerle kurgulanması, diğer hacim akustik parametrelerinin (erken sönümlenme süresi, ses basınç seviyeleri farkı, konuşmanın iletim indeksi, konuşmanın belirginliği, netlik vd.) uygun değerlerde oluşturulmasında etkili olmaktadır [3]. Özellikle konuşma eylemi bulunan salonlarda konuşmanın anlaşılabilirliğini sağlamak için reverberasyon süresinin kontrolü önemli bir hacim akustiği parametresi olarak değerlendirilmektedir [4]. Eldakdoky ve Elkhateb tarafından yapılmış olan çalışmada konuşma eylemi amacıyla tasarlanan mevcut salonlarda konuşmanın anlaşılabilirliği; reverberasyon süresi ve iç mekân yüzey bileşenleri (tavan ve duvarlar) üzerinden araştırılmış ve incelenmiştir [5]. ...
Konuşma eyleminin bulunduğu hacimlerde, akustik performansın oluşturulmasında öznel ve nesnel hacim akustik
parametreleri ele alınmalıdır. Bu çalışmada, mevcut durumda bulunan Irak-Necef İslam Üniversitesi Alawiya
Konferans Salonu’nun konuşma eylemine yönelik reverberasyon süresi üzerinden akustik performans
değerlendirmesi yapılmıştır. Çalışma kapsamında, hacim akustiği çerçevesinde öznel ve nesnel parametreleri
etkileyen reverberasyon süresinin kontrolü üzerinde durulmuş, hacim içi reverberasyon süresi ve hacmin yüzey
yutuculuklarının ilişkisi incelenmiştir. Mevcut durumda yerinde ölçümler yapılarak reverberasyon süresi tespit
edilmiştir. Mevcut salonun reverberasyon süresinin kontrol edilmesine yönelik; ses yutuculuk katsayılarına göre
seçilen malzemeler, farklı konumlandırılarak alternatif modeller oluşturulmuştur. Oluşturulan alternatif modellerin
reverberasyon süreleri, akustik analiz için kullanılan ECOTECT v.5.20 bilgisayar simülasyon programı aracılığıyla
belirlenmiş ve ışın izleme yöntemi ile geometrik akustik analizleri yapılmıştır. Modellerin karşılaştırılması ile
hacim içi konuşma eylemine yönelik uygun reverberasyon süresinin elde edilmesinde yüzey yutuculuklarının etkisi
analiz edilmiştir. Çalışma sonucunda kare planlı, düz zeminli ve yüksek tavanlı (en az 6 m) salonlarda konuşma
eylemine yönelik duvar, tavan ve döşeme bitiş malzemeleri konumlarının ve yüzey yutuculuklarının reverberasyon
süresine etkileri değerlendirilmiştir.
... In university classrooms, this latter factor -the human noise -is generally higher than the other two, due to the large number of listeners. It has been proved that the human noise depends on the occupancy degree and its value may increase in presence of PA [6,7]. ...
The background noise has a fundamental role in oral communication, since the higher the speech level with respect to the background noise the greater the intelligibility. In occupied lecture halls the main contribution to background noise is related to the human noise, which is called by scholars student activity. Scholars proposed methods to measure both student activity and speech level through short-time sound level meter measurements during lessons. However, a comparison of their relative effectiveness on a relevant set of data in different situations is still lacking. In this study, basing on recordings of university lessons performed with public address system, student activity and speech level values were extracted using different methods. Various scenarios of university lectures were recorded: frontal lessons , media-aided lectures, open discussions. Visual-segmentation and blind-segmentation procedures were compared for each case. Results show the benefits of blind-segmentation methods, which seem to be reliable and affordable methods for this kind of analyses.
... Speech intelligibility in rooms is influenced by both the level of speech and ambient noises and acoustic characteristics of the room. Higher speech to noise ratios usually result in greater intelligibility of speech (Reich & Bradley, 1998). ...
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 dB and –3.73 dB 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 dBA and 47.8 dBA to meet the minimum level for a “good” class (U50 = 1.5 dB) and the middle level for a “fair” class (U50 = –1.0 dB).
By means of measurements of syllable comprehension, retelling of foreign language texts and mathematics tests, the negative influence of spatial acoustic conditions in lecture rooms on the achievements of pupils is objectively established. The investigation was preceded by a survey of the size, shape and construction of the available lecture rooms and by electroacoustic measurements of spatial acoustic conditions in conventional and space-acoustically treated lecture rooms.
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.
A classroom's acoustic design should be constructed so that the highest possible degree of speech intelligibility is achieved for teachers and pupils. Yet classrooms are a noisy and a reverberant environment for speech communication. The aim of this study was to find out the acceptable acoustic conditions for speech intelligibility measured with the RASTI method, using a minimum amount and the proper placement of mineral wool in a quiet test classroom. To reach an excellent acoustic environment where the mean RASTI value was 0.75 or higher, it is necessary to use mineral wool at least at an area of 30% of the maximum absorption area of the room and to place it on two surfaces.
An observer in an auditorium receives first the direct sound from the source and after that a large number of reflections from the different surfaces in the enclosure. This very intricate sound pattern is analysed by the hearing system and gives rise to those acoustical qualities normally attributed to the auditorium.The present article summarizes the work carried out in this laboratory with the object of throwing more light on the interpretation, by the hearing mechanism, of reflection patterns in auditoria and the application of these principles to the design of auditoria.
The concept of the Modulation Transfer Function (MTF) can successfully
be applied to evaluate the quality of speech transmission from a
talker to a listener in an auditorium. Typically, depending on the
auditorium acoustics, the intensity modulations contained in the
original sound are to some extent reduced when measured at a listener's
location, especially for higher modulation frequencies. The implementation
of such an acoustical MTF analysis with a sinusoidally modulated
test signal is described in detail. The performance of a sound transmission
system as revealed by the MTF can be expressed in one single index
(the Speech Transmission Index, STI), which relates well to the performance
as determined by intelligibility tests with talkers and listeners.
A review is given of a series of studies on various aspects of the
chain of relations between auditorium acoustics, MTF, STI, and speech
intelligibility, illustrating the use of this approach for estimating
speech intelligibility, either from MTF calculations at the design
stage of an auditorium or from MTF measurements in actual situations.
xiii, 148 leaves : ill. ; 31 cm. PolyU Library Call No.: [THS] LG51 .H577M ME 2006 Cheung The classroom is the place in which spoken language communication takes place to enable students to learn essential knowledge. Thus, the classroom can be defined as a communication channel for learning. My research is to focus on the special requirement and parameters placed on this communication channel by the listeners. The objective of my is to quantify the effects on the listeners in terms of their age, hearing status and background knowledge status. In addition, English, Cantonese and Mandarin proficiency on speech intelligibility in silent or noisy area is also examined to find out the signal-to-noise ratios that enable all students to obtain high intelligibility. The purpose of these studies is to apply different parameters such as "signal-to-noise ratio", "early decay time"(EDT), "speech transmission index"(STI) and "reverberation time"(RT) to predict the classroom characteristics. Besides, analysis of the younger generations for whom Cantonese, Mandarin and English are either their first or secondary language will be reported. Finally, various methods of estimating signal-to-noise ratios at different positions inside the classroom will be introduced, such as "ray tracing and image source method of computer simulation" and "Rapid Speech Transmission index"(RASTI) estimation in "Maximum Length Sequence System Analysis"(MLSSA), which predicts the intelligibility of different languages. M.Phil., Dept. of Mechanical Engineering, The Hong Kong Polytechnic University, 2006
The speech transmission index, the useful-to-detrimental ratio, and the percent articulation loss of consonants are three quite different types of measures of speech intelligibility in rooms. They each combine a measure of the speech-to-noise ratio and a measure of the room acoustics to better relate to speech intelligibility in rooms. Values of all three types of measures were calculated from 91 room impulse responses obtained from a wide range of acoustical conditions, and for different speech-to-noise ratios. Several forms of these measures are shown to be reasonably well related to each other. The calculated regression equations relating the various measures of speech intelligibility permit practical conversions among the measures.
The data from two previous studies of speech intelligibility in rooms are used to derive values of acoustical measures that would correspond to optimum conditions for speech in rooms. Optimum values of the A-weighted signal-to-noise ratio, the articulation index, the speech transmission index, and the 0.080-second useful-to-detrimental ratio were first determined as the point beyond which no increase in mean speech intelligibility score would be expected. Combinations of optimum reverberation time and background noise level were calculated from equal useful-to-detrimental ratio contours. These optimum reverberation time and background noise levels are presented as simple design contours. L'auteur utilise les données de deux études antérieures sur l'intelligibilité de la parole dans les salles pour dé terminer des valeurs de mesures acoustiques qui correspondent aux conditions optimums de transmission de la parole en salle. Les valeurs optimums du rapport signal- bruit de valeur pondérée A, de l'indice d'articulation, de l' indice de transmission de la parole et du rapport utile- nuisible de 0,080 seconde ont d'abord été déterminées comme constituant le point au-delà duquel on ne peut espérer augmenter l'indice moyen d'intelligibilité de la parole. Les combinaisons du temps de réverbération et du niveau de bruit de fond optimums ont été calculées à partir des é quicontours du rapport utile-nuisible. Ces temps de réverbé ration et niveaux de bruit de fond optimums sont présentés sous forme de contours simples de conception des salles. RES
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.