Optimum Reverberation Research Articles

Evaluation and Improvement of Reverberation Time in the Current Enclosed Spaces with Speech Action

There are subjective and objective acoustic parameters in the creation of acoustic performance for speech action in room acoustics. Control of reverberation time affecting subjective and objective acoustic parameters is a main parameter in room acoustics. In this study, the acoustic performance assessment of the TOBB Twins Headquarters Reception Hall, which is current enclosed space with square plan and flat floor, has been performed as a case study. The evaluation focused on the relationship between reverberation time and interior surface absorption. Primarily, the reverberation time was determined according to the international standard with in-situ measurements in the current enclosed space. The reverberation time of the space was found over the reference value range. Models have been developed with the use of materials to reduce the reverberation time. In the assessment of room acoustics parameters, reverberation times of the models developed using Ecotect v.5.20 and Odeon 14.00 simulation programs have been determined. The model in which the optimum reverberation time for the speech action was obtained was constructed. After the construction, reverberation time measurements have been made again. As a result of the study, the effect of surface absorptions on the improvement of reverberation time in the enclosed spaces with square plan and flat floor for speech action has been evaluated. Suggestions have been developed to control the reflective and absorption properties of all surfaces in accordance with the evaluation and improvement of reverberation time.

Reverberation times preferred by traditionally trained versus classically trained musicians for overall impression of contemporary gugak orchestras using auralisation techniques

Gugak encompasses the traditional music of Korea to contemporary music developed based on traditional music. Gugak orchestra music performed in a concert hall is a new type of music in the 20th century that combines traditional musical instruments of Korea and the form of a Western symphony orchestra. The optimal reverberation time for gugak is controversial. In the present study, the optimal reverberation time specifically for gugak instrumental solos, traditional gugak court ensemble, and orchestra music is investigated in an auralised concert hall measuring 18,838 m3 in volume.The preferred reverberation time (mean of 500 Hz and 1 kHz) is discovered to be 1.7 s among 1.1, 1.7, 2.1, and 2.6 s for both gugak and classical musician groups, regardless of the music sources. The optimum reverberation times derived are 1.78 s for gugak musicians and 1.95 s for classical musicians from the preferred reverberation times, consistent with the optimum reverberation times as a function of room volume in traditional concert hall studies. Subtle differences in the optimum reverberation times are observed between the two musician groups; however, the results support that the optimum reverberation times for gugak are affected by the room volume rather than the musical characteristics.

The mixture material of dried straw and kapok for acoustic treatment for UTeM mosque

The acoustical requirements in terms of intelligibility and liveliness are dissimilar for both of sounds-recitation and speech on religious subjects at UTeM mosque. To attain an overall satisfactory acoustical performance, it is significant to find an optimum Reverberation Time (RT) and the best directivity, which is the major factors affecting intelligibility and liveliness. This experiment is conduct to gauge the effect of RT by making it a variable, while keeping other factors as non-variable and fulfilling ideal conditions for maximum intelligibility. Bearing in mind, the acoustical problems always occurred in any communication building. To improve the problem, this paper presents the new idea of improvement by using biodegradable sound absorber materials which is the mixture of dried rice straw and kapok.

A research on acoustical comfort for hearing-impaired individuals in inclusive education places

The inclusive education method has substantial contributions to hearing-impaired individuals’ education and socialization. However, the poor physical environment and acoustic comfort conditions negatively affect speech intelligibility at such places and therefore, the quality of education. Upon determining that there are very few subjective evaluation studies, we conducted a study regarding the impact of acoustic comfort conditions on speech intelligibility at inclusive education places. Within the scope of the study, first, a classroom was determined, and the current acoustic conditions of the class were evaluated objectively by field acoustic measurements. A calibrated model was created in the simulation software of the relevant class and then two more models with optimum reverberation time values of 0.4 s and 0.8 s as suggested in the literature, and auralizations were performed for the models. For subjective evaluation, a subject group of hearing-impaired and normal hearing individuals fulfilling equal conditions were tested by speech discrimination test in real-time in the classroom and from auralization recordings in a laboratory setting. Regarding the results obtained, it was observed that speech intelligibility percentage of normal hearing individuals increased as expected while in hearing-impaired individuals, contrary to the expectations, percentage differed from one another, and there was no increase. Following the discussions with experts, it was concluded that different hearing aids used by hearing-impaired individuals might lead to this situation. Accordingly, it occurs that the possibility to achieve a good speech intelligibility for hearing-impaired individuals even if optimum acoustic values suggested are fulfilled in education places remains unclear.

Variation of Subjective Responses by Acoustic Performance Improvement of the Community Sports Facilities with Lightweight Panel

The recent improvement in the quality of living has led to greater interest in health and to constant establishment of community sports facilities which are not dependent on seasons or weather. However, lightweight panel, which is convenient and cheap, has been used as a finished material for most of the existing community sports facilities, which, thus, have acoustic defect with excessive echoes. Although acoustic simulation is used to change finished material and improve acoustic performance, there are significant differences from subjective satisfaction among people after the improvement. From this perspective, this study aimed to conduct a psycho-acoustic experiment to see the variation in subjective responses among people on the basis of the data concerning acoustic performance in community sports facilities finished with lightweight panel. After improving acoustic performance in terms of optimum reverberation time in community sports facilities where acoustic defect was found, such evaluation vocabularies as “reverberant”, “loudness”, and “diffusion” got lower responses while “intimacy”, “definition”, “clarity”, “warmth”, and “balance” got higher responses. It was therefore found that subjective responses could be improved along with the improved acoustic performance in community sports facilities with the problem of excessive echoes. It is expected that this study will be able to provide useful data for improving acoustic performance in similar community sports facilities.

Waktu Dengung Ruang Sholat Masjid Desa Berdasarkan Perbedaan Bentuk Plafon

Mosque’s prayer hall needs optimal reverberation time to get clear sound in the mosque, especially during praying. Praying rites need clear sound . “Desa’s” mosques are dominant in quantity in Indonesia. They had many different types. The difference of geometric form affected acoustic performance. In this study, Desa’s mosques would be observed according to their space form: dome, tajug (crown), and flat ceiling. This study would observed six samples of prayer hall, with two samples for each type/form of ceiling: two samples for prayer hall with dome ceiling, two samples for prayer hall with crown ceiling, and two samples for prayer hall with flat ceiling. The result shows that there were no space-ceiling that have optimum reverberation time (RT). All space ceiling type have higher RT than the RT standart. It shows that all the samples perform bad quality of acoustic. According to this research, the best form of ceiling was flat ceiling, while dome ceiling was the worst ones. Keywords: reverberation time, prayer hall of mosque, form of ceiling

Calculating the Optimum Reverberation Time and Absorption Coefficient for Good Speech Intelligibility in Classroom Design Using U50

Acoustical comfort in general, and the quality of speech transmission from teacher to students in particular, are crucial in determining the quality of educational processes in schools. The acoustical treatment of interior surfaces, the sound insulation of surrounding constructions, the vocal capacity of the teacher, student activity noise, children's abilities to hear and concentrate and the educational circumstances, are among the many factors in the complex mechanism of speech understanding. Managing the rich variety of measures for optimising classroom acoustics demands a multidisciplinary approach. In this article we propose a predictive model for speech intelligibility, as expressed with the parameter U50, based on objective acoustical values, i.e. the reverberation time RT, signal-to-noise ratio SN, and the relative proportions of sound arriving early and late at the listener. The present article introduces the model and derives guidelines for architectural design. The model is illustrated using a typical Dutch classroom as an example. Architectural guidelines are derived for maximum RT values, and compared with existing recommendations. The possible additional need for minimum RT values is also investigated in relation to the phenomenon of 'overdamping' in classrooms.

School music rehearsal spaces—How dry is dry enough?

Handbook values for optimum reverberation time (RT60) in a music studio, such as a school band or chorus rehearsal space, fall into the 0.8 to 1.0 second range, depending on volume. One music room furniture manufacturer specifies RT60 values as high as 1.91 seconds. We submit that these RT60 values are excessive. The Classroom Acoustical Standard (ANSI S12.60-2002) specifies a maximum allowable RT60 of 0.7 seconds to achieve good speech intelligibility. Obviously, good speech communication is necessary for effective education of any kind. In special function rooms designed for music instruction, experience has shown that the design target RT60 should be as low as 0.2 seconds, for frequencies of 500 Hz and above. The requirement for such low reverberation is dictated by the need to reduce the extremely high sound levels that can be generated by a large group; and to give the instructor a dry environment that provides the ability to isolate, identify, and evaluate the musical performance of an individual student while rehearsing in a larger group. This allows the instructor greater opportunity to reinforce good student musicianship and to correct individual student mistakes, ultimately resulting in a higher level of concert performance. Sonic examples are given.

Optimum Reverberation for Speech Intelligibility for Normal and Hearing-Impaired Listeners in Realistic Classrooms Using Auralization

The objective of this study was to use auralization techniques to investigate the optimal reverberation for speech intelligibility for normal-hearing and hearing-impaired adult listeners in classrooms with non-diffuse sound fields. This extended a previous study involving rooms with diffuse sound fields to more realistic rooms. Modified Rhyme Test (MRT) signals were auralized in six virtual classroom configurations with different reverberation times. Each classroom contained a speech source, a listener at a receiver position, and a noise source located between the talker and the listener. Two speech- and noise-source output-level differences (0 and +4 dB) were tested. Subjects performed speech-intelligibility tests in the virtual classrooms to identify the reverberation time that gave the best results in each case. For both normal and hearing-impaired listeners, the optimal reverberation time was generally non-zero, and increased with decreased speech-to-noise level difference. Hearing-impaired subjects apparently required more early energy than normal-hearing subjects. The optimal reverberation time for speech intelligibility in classrooms is not necessarily zero, as is commonly believed. The optimal value is generally non-zero, and varies with the room, the locations of the speech and noise sources and the listener, and the noise level.

Why we should design for optimum reverberation times in rooms for speech communication

Various texts list recommendations for optimum reverberation times as ideal goals in rooms for speech communication. However, some newer documents, such as ANSI S12.60, talk about maximum recommended reverberation times in rooms for speech communication. The source of the changed approach can be traced to interpretations of experimental results that do not consider the full implications for speech communication in real rooms, and also to the fact that reverberation time is not an ideal predictor of the quality of speech communication. In the extreme, minimizing reverberation times would lead to near anechoic rooms for speech and inadequate signal-to-noise ratios. The need for optimum reverberation times can be explained as a simple need to first achieve adequate signal-to-noise ratios. However, a more complete understanding is obtained by examining the benefits of early-arriving reflections of speech sounds on the intelligibility of the speech to listeners. Attempts to determine optimum reverberation times for normal hearing listeners, which are based on a balance between avoiding excessive reverberation and maintaining adequate signal-to-noise ratios, lead to a range of acceptable values that can vary with the ambient noise level. This discussion will be supported with examples from room acoustics measurements in classrooms and meeting rooms.

Auralization study of optimum reverberation times for speech intelligibility for normal and hearing-impaired listeners in classrooms with diffuse sound fields

Speech-intelligibility tests auralized in a virtual classroom were used to investigate the optimal reverberation times for verbal communication for normal-hearing and hearing-impaired adults. The idealized classroom had simple geometry, uniform surface absorption, and an approximately diffuse sound field. It contained a speech source, a listener at a receiver position, and a noise source located at one of two positions. The relative output levels of the speech and noise sources were varied, along with the surface absorption and the corresponding reverberation time. The binaural impulse responses of the speech and noise sources in each classroom configuration were convolved with Modified Rhyme Test (MRT) and babble-noise signals. The resulting signals were presented to normal-hearing and hearing-impaired adult subjects to identify the configurations that gave the highest speech intelligibilities for the two groups. For both subject groups, when the speech source was closer to the listener than the noise source, the optimal reverberation time was zero. When the noise source was closer to the listener than the speech source, the optimal reverberation time included both zero and nonzero values. The results generally support previous theoretical results.

Auralization study of optimum reverberation for speech intelligibility for normal and hearing-impaired listeners

Reverberation and signal-to-noise level difference are two major factors affecting speech intelligibility. They interact in rooms. Past work has accounted for noise using a constant received background-noise level. Noise is actually generated by sources, and varies, and affects speech intelligibility differently, throughout the classroom, depending on where the sources are located. Here, a speech-babble noise source located at different positions in the room was considered. The relative output levels of the speech and noise sources, resulting in different signal-to-noise level differences, were controlled, along with the reverberation. The binaural impulse response of a virtual idealized classroom model was convolved with the Modified Rhyme Test (MRT) source and babble-noise signals in order to find the optimal configuration for speech intelligibility. Speech-intelligibility tests were performed with normal and hard-of-hearing subjects in each of 16 conditions which were combinations of reverberation time, signal-to-noise level difference, and speech- and noise-source locations. For both normal and hearing-impaired subjects, when the speech source was closer to the listener than the noise source, the optimal RT was zero. When the noise source was closer to the listener than the speech source, the optimal RT was generally non-zero. This agrees with theoretical results.

Optimum reverberation time for speech intelligibility in classrooms

This work addresses the topical question of the optimum reverberation time (RT) for speech intelligibility in classrooms. Existing literature is reviewed and is found to be inconsistent. Experimental methods generally predict zero optimum RT, while theoretical methods predict nonzero values. These differences are discussed; they appear to stem from different treatments of the background noise. Assuming diffuse-field theory, a theoretical model to predict optimum RT was developed from a previously proposed model [S. R. Bistafa and J. S. Bradley, J. Acoust. Soc. Am. 107, 861–875 (2000)]. It incorporates noise in a physically realistic way and predicts nonzero optimum RTs. Subsequently, to reduce reliance on diffuse-field theory, the model was modified using empirical methods to predict speech level and reverberation times in classrooms [M. R. Hodgson, J. Build. Acoust. (in press, 2001)]. Again, nonzero optimum RTs were predicted. The prediction models and results are presented, practical conclusions are drawn, and suggestions for further work are made.

A New Approach to Optimum Reverberation Time Characteristics

Subjective effects of the whole reverberation process, including the sound fading process, are focused on in this study. The concept of “subjective reverberation length (SRL),” an impression of time length in the reverberation decay process, is introduced. Systematic hearing tests on SRL using artificial reverberation signals are introduced first. Then a hypothesis on the perception of SRL and “equal SRL contour” are derived from discussions on the auditory mechanism to determine SRL. Finally, a reverberation time ratio curve for frequencies is proposed as the optimum reverberation characteristics for music based on the equal SRL contour. The proposed curve has a relatively gentle slope in the low frequency range, and agrees well with the recommendations by Jordan (1980), Beranek (1962) and Yamamoto (1973), which have been well received recently.

Optimum r/t of music studios suited to Indian music

In acoustic design of music studios for the All India Radio network, recommendations made by Morris and Nixon for reverberation time are followed. The typical volume of a normal music studio is of the order of 4500 ft 3 and its reverberation time at 1 kHz is chosen around 0·5 s. During the last few years, there has been a feeling that there is a need to enliven the studios. A study was carried out to find the optimum reverberation time (R/T) of music studios suited to Indian music. It was observed that an R/T of 0·6 s appears to be, in general, an acceptable figure.

Testing classroom acoustics

For speech to be intelligible in classrooms, the reverberation time of sound should be reasonably short, allowing for the sound intensity required for the absorption characteristics. This optimum reverberation time is, in turn, related to the volume of the room and the degree of occupancy. Following field measurements in different types of schools in Egypt, the optimum ratios for local circumstances are suggested by a member of the Acoustics Department of the Building Research Centre at Dokky, Cairo.

An Optimum Reverberation Time for Mosques in Bangladesh

For a mosque in Bangladesh, the acoustical requirements in terms of intelligibility and liveliness are dissimilar for the types of sounds - recitation from the Holy Koran and speech on religious subjects. To attain an overall satisfactory acoustical performance, it is significant to find an optimum Reverberation Time (RT), which is one of the important factors affecting intelligibility and liveliness. Experiment is conducted to find the effect of RT by making it a variable, while keeping other factors as non-variable and fulfilling ideal conditions for maximum intelligibility. Preferences are judged on pairs of sound clips of recitation and speech, for both intelligibility and liveliness, on a 5-point scale and findings are analysed thorough the statistical method of paired comparison. Considering preferences of all aspects the optimum RT is proposed as 0.9 s for an overall balanced acoustical performance for both recitation and speech for a mosque in Bangladesh. Keywords: Intelligibility, Liveliness, Mosque, Recitation, Reverberation time, Speech. DOI: 10.3329/bjsir.v44i2.3667 Bangladesh J. Sci. Ind. Res. 44(2), 163-170, 2009

The acoustics of rooms

The propagation of sound in rooms is discussed. Sabine's formula for reverberation time is derived as an approximation to Eyring's formula. The relation between optimum reverberation time and use of a room is considered. Finally, the investigation and treatment of an acoustically poor room are described, illustrating the improvement obtained by the use of sound-absorbing materials.

Optimum Acoustic Criteria of Concert Halls for the Performance of Classical Music

In recent years one has found essential criteria of room acoustics which are responsible for good intelligibility of speech addresses in auditoria. Concert halls which have been built according to these principles are not fully satisfying as to the performance of classical music. The high intelligibility which one deduces from the first reflection pulse and the envelope of the decay curve is not of primary importance for classical music which demands, above all, fullness of tone and blend. An opportunity was afforded to go on tour with the Cleveland Orchestra and to make statistical measurements in 15 different auditoria during their concerts. It has been resulted that the dynamic range attainable by the orchestra is directly dependent on room acoustic qualities. The lower limit of loudness is given by the noise level, variable in the different halls, and the upper limit by diffusion and absorption which are also responsible for the quality or timbre. The behavior of the orchestra is revealed further from the tempo of the music, with the tendency that in the better concert hall with the optimum reverberation time little absorption and good diffusion allow a faster tempo.

Reverberant Concert Halls and Churches Can Be Good for Speech

An intermediate frequency tweeter placed high above the rostrum and fed with frequencies 1000 to 10 000 having correct vertical and horizontal angular distribution beamed on the audience and not on walls and ceiling will crisp up consonants without adding to reverberation. Kuhl recently found (by tape recordings to eliminate prejudice) that optimum reverberation of concert halls for symphony music is 1.6 to 2.1 sec independent of size, contrary to the usual idea that it is proportional to the cube root of volume. Two seconds also is probably optimum for churches when full and adds much to inspirational effect of both the music and the sermon. For plays it is desirable to have a reverberation of under 1 sec to avoid overlapping of syllables, but in a sermon the speech is much slower so that 2-sec reverberation usually does not blur the words. However, for the occasional fast-speaking minister, the above P.A. system will make the speech quite audible despite long reverberation. Even plays can be put on if several microphones are distributed along the front of the platform. A 10-μf condenser should be put in series with the speaker to protect it from accidental frequencies below 1000.