Reverberation Time Research Articles

Assessing acoustical quality in university classrooms in Brazil: Measurements and simulations

The acoustic quality of learning spaces, such as classrooms, is a worldwide issue. Some countries have regulations or guidelines for these environments, which does not happen properly in Brazil. Beyond the lack of nationwide research related to classroom acoustics, Brazil has two standards with a few information related to classroom acoustics. One of them was written in 1992, having a single demand concerning an appropriate reverberation time for conference rooms at the 500 Hz frequency, without detailed requirement, in contrast to other national guidelines. Another one, updated in 2020, recommends the sound pressure levels for indoor environments, having classrooms in its list. The aim of this study is to analyze the acoustic quality of two Brazilian classrooms over a public university in the south part of Brazil. Several impulse responses were taken within the learning environments and then processed in Matlab with the ITA ToolBox. The classrooms were also modeled into RAVEN and I-SIMPA software aiming to identify different sound absorption schemes to improve their speech intelligibility. The findings showed that the classrooms had a bad acoustic environment, with a measured reverberation time of approximately [Formula: see text]. However, the simulation suggested that implementing sound absorption strategies could reduce the reverberation effects by half, bringing it closer to optimal levels. The estimated costs for implementing sound absorbers were [Formula: see text] for Classroom 01 and [Formula: see text] for Classroom 02.

Integration of Acoustic Metamaterials Made of Plastic to Improve Building Acoustics

Abstract According to the Waste Management Policy of the European Union, the recycling and reuse of various wastes is considered the most environmentally friendly and advanced waste disposal technology that has the least impact on the environment. By applying the principles of the Circular Economy, plastic waste will extend its life cycle and will be used as secondary materials to create metamaterial structures with improved sound absorption and insulation properties. The aim of this study was to determine plastic potential for use in acoustic structures. Acoustic metamaterial resonators, created from plastic, were measured in an impedance tube according to standards ISO 10534-2 for their sound absorbing and ASTM E2611 for their insulating properties. Two types of plastic, PLA and recycled PET-G, were used in acoustic metamaterial 3D printing process. For sound insulation, combined resonator systems were used to control symmetrical wall sound resonance. Sound absorption of both PLA and PET-G metamaterials were peaking at 1600 Hz with 0.93 and 0.89 sound absorption coefficient, respectfully. The results showed that combined constructions with plastic metamaterials can be integrated into building structures and used as an alternative for improving building acoustics, reducing indoor noise and reverberation time.

Just noticeable difference for simulation accuracy between full and reduced order models (L).

Model order reduction techniques significantly reduce the computational time when performing accurate room acoustic simulations with numerical methods that inherently include all the wave phenomena. There is a clear trade-off between physical accuracy and acceleration, but how humans perceive these errors is unknown. This study aims to investigate physical error limit that does not induce perceptual differences. Various two-dimensional rooms and reverberation times are tested with a three-alternative forced-choice listening test. Results reveal that for the presented cases, the threshold stands between a relative root mean square error of 1% and 0.1%, where the reduced order model stimulus results in a statistically significant difference.

Room acoustics of Mycelium Textiles: the Myx Sail at the Danish Design Museum

Abstract Taking the Myx Sail displayed at the Danish Design Museum as a case study, this article investigates the room acoustics of an architectural installation made of Mycelium Textiles. Mycelium Textiles represent a novel typology of mycelium-based composites (MBC). The Myx Sail absorbers are grown on a composition of different layers of plant fibres combining woven jute textile with hemp mat and loose wood wool substrate enhancing the mechanical and acoustic properties of the composite. Two complementary acoustic tests were conducted to measure the absorbing properties of the mycelium material and its effects on the acoustics of the exhibition hall. The results show that the sail acts effectively as an acoustic absorber especially in higher range of frequencies, reducing the reverberation time and improving speech intelligibility. The effect of the sail on the overall room acoustics is especially effective, if the sound source is placed directly underneath the sail. The results of a complementary survey amongst visitors on their subjective perception of comfort and well-being however indicate that the degree to which a grown surface (and by extension, a grown building) is perceived positively or negatively depends on the relationship the individual has with Nature.

STUDI KENYAMAN AKUSTIK PADA RUANG AULA BMKG STASIUN KLIMATOLOGI KELAS 1 DELI SERDANG

<p>The purpose of this study was to determine the acoustic comfort level of the BMKG Hall Class 1 Deli Serdang Climatology Station before and after the treatment of the room in the form of adding sound-absorbing materials. The purpose of this study was to measure the noise level and optimize the effect of noise with acoustic comfort standards in accordance with KEPMENLH No. 48 of 1996 concerning Noise Level Standards in the BMKG Hall of Class 1 Deli Serdang Climatology Station. Sample Materials The materials used for sound absorption in the room are newsprint pulp and cork waste (Styrofoam) with a thickness of 3 cm. This research is motivated by the high noise below in the room which causes hearing discomfort in the room. The results of the physical test of newsprint and cork pulp (Styrofoam) at frequencies of 125 Hz, 250 Hz, 500 Hz, 1000 Hz, 2000 Hz, and 4000 Hz obtained absorption coefficients of 0.47, 0.36, 0.48, 0.36, 0.55 and 0, 59 with the results of Reverberation Time (RT) calculations at frequencies of 125 Hz, 250 Hz, 500 Hz, 1000 Hz, 2000 Hz, and 4000 Hz, the results obtained are RT 2.13 s, 1.35 s, 1.01 s, 0.80 s, 0.79 s, 0.82 s.</p>

OPTIMIZING THE ACOUSTIC CONDITION OF A PYRAMIDAL-CEILING MOSQUE BASED ON SIMULATION

This study aims to optimize the acoustic condition of a pyramidal ceiling mosque utilizing a simulation approach. The simulation was done using I-Simpa, simulating the room acoustic parameters of 15 m x 15 m x 5 m and a 5 m roof height of a mosque. The optimization was accomplished by varying the occupancy level and using absorbent materials. The best acoustic condition was defined as having a high level of speech intelligibility (C-50 > -2 dB) yet the longest possible reverberation time, especially at 500-4000 Hz. The simulation indicates that the speech intelligibility value increases with the number of filled rows, both with and without sound-absorbing material. On the other hand, the reverberation time is unaffected by the number of filled rows and is extended by using sound-absorbing materials. Hence, without sound-absorbing ceiling material, optimal conditions are attained when the mosque is fully occupied. Meanwhile, using sound-absorbing materials on the mosque's ceiling establishes optimal acoustic conditions for all occupancy levels. It demonstrates that using sound-absorbing materials improves the acoustic quality of the pyramidal-ceiling mosque.

Investigation of the Acoustics Performance of the University’s Lecture Rooms by using Economical and Feasible Design Improvement Strategies

Students encounter difficulties in speech comprehension because of unfavorable classroom acoustics conditions, which subsequently affect their cognitive development and academic performance. Therefore, optimal listening conditions are required to ensure that listeners perceive and recognize speech effectively. This invites numerous studies to explore plausible acoustic interventions and treatments as an initiative to remediate the issue. Thus, this study seeks to a) identify the actual acoustic conditions in two (2) classrooms in the Faculty of Built Environment, Universiti Malaysia Sarawak, and b) establish economical acoustic design strategies for future improvements. This quantitative study embarks on on-site acoustic measurements to evaluate the reverberation time and background noise level of the selected classrooms. The data from the on-site measurement is applied for 3D model verification for the simulation process. The establishment of plausible design treatment alternatives is further analyzed through simulation using ODEON software. The simulation process yielded the effects of a) material surface treatment and b) sound field amplification systems on several acoustic parameters. The findings reveal that the surface treatment using low-cost material and the installation of sound field amplification significantly enhanced the classroom acoustic quality and are feasible to be implemented for future improvements.

Investigation of acoustic comfort, productivity, and engagement in naturally ventilated university classrooms: Role of background noise and students’ noise sensitivity

Optimal classroom acoustics enhance students' engagement and learning efficiency. In warm-humid climate, ceiling fans are used at different speeds to enhance thermal comfort in naturally ventilated classrooms. Although ceiling fans enhance thermal comfort, using fans at higher speeds significantly increases Background Noise (BGN), interfering with acoustic comfort. To achieve an optimal acoustic environment, it is important to understand the effect of BGN on acoustic comfort. Hence, focusing on ceiling fan noise in classrooms, this study investigates the effect of acoustic environment and students' noise sensitivity on acoustic comfort, productivity, and engagement. A four-month-long field study was conducted in 11 naturally ventilated classrooms, obtaining 828 responses. Sound pressure levels in active classrooms were measured to calculate BGN and Signal-to-noise ratio (SNR). Reverberation time (RT) was measured both in students' presence and absence. Acoustic comfort conditions, productivity, and engagement of students at every seat were obtained through questionnaire survey. BGN levels and RT ranged from 58.2 to 65.3 dBA and 0.7–2.1 s, respectively. A positive correlation was found between acoustic comfort and engagement level and productivity. Regression analysis showed that students with high noise sensitivity reported acoustic discomfort when the BGN exceeded 62.4 dBA, RT was above 1.7 s and SNR was below 3.7 dBA. Chi-square test involving the acceptability vote indicated that students were more likely to accept the BGN ≤61 dBA, RT ≤ 0.7 s, and SNR ≥6.5 dBA. This study establishes the relation of BGN, RT, and SNR with acoustic comfort in naturally ventilated classrooms, offering insights for classroom acoustic environment enhancement.

Vocal Demand Response to the Educational Setting Based Communication Scenarios: A Single Subject Study

Objectives. This was a single-subject study, aimed to demonstrate different vocal demand situations that are typical for primary school and teacher's vocal demand response under two acoustical conditions, with and without voice amplification, during five working days. Methods. The long-term voice dosimetry with Vocal Holter Med (PR.O. Voice Srl) was carried out on a 49-year-old female teacher with voice disorders during daily teaching activities. A sound field amplification system (SFAS) PentaClass Runa was installed in the classroom. Voice dosimetry was provided under two different acoustical conditions: without SFAS (2 days) and with SFAS (3 days). Results. Phonation time percentage, sound pressure level (SPL), SPL SD, fundamental frequency (F0), F0 SD, cycle, and distance doses were investigated in seven communication scenarios (lessons, group/individual classes, sports lessons in the gym and schoolyard, breaks, lunch breaks, and other activities). The median scores of all voice parameters differed significantly between different vocal demand contexts. The significant statistical difference in the vocal demand response was in the communication situations with and without SFAS. In addition, the number of children, reverberation time, and ambient air relative humidity impacted voice SPL and the cycle dose. Conclusions. Lessons, sports lessons held in the gym or schoolyard, breaks, and lunch breaks were considered as high vocal demand communication situations requiring higher voice intensity and fundamental frequency, higher phonation time percentage, cycle, and distance doses. Group/individual work and other teacher activities during the day, unrelated to direct work with students, were categorized as low vocal demand communication scenarios.

Peculiarities of a Rarely Used Method of Measuring the Speech Transmission Index in Premises

Evaluation of speech transmission index (STI) in premises allows for determining the speech intelligibility, and therefore the suitability of premises for speech communication. STI measurements using the speech transmission index for telecommunication systems (STITEL) method are rarely performed in rooms, possibly due to insufficient information on the accuracy of this method. In this paper, computer simulations were used to estimate the STI estimation errors by the STITEL method under conditions of noise and reverberation. The pink noise model and the room impulse response estimate of a real room with a reverberation time T60=0.8 s were used for the research. The duration of the test signals varied between 4, 8, 16, 32, and 64 seconds, and the signal-to-noise ratio varied from minus 28 dB to plus 28 dB. The dependences of the bias, standard deviation, and total error of the STI estimate on the duration of the test signal and the signal-to-noise ratio are obtained. It is shown that the total error of the STI estimation is close to 0.03 when the duration of the test signal is 8 s. Under conditions of noise action, this error decreases with a further increase in the duration of the test signal. Under conditions of joint action of noise and reverberation, such a decrease was not observed, while the total error is within 0.03-0.04.

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.

Assessment of acoustic comfort in a hostel building inside an educational campus

In the contemporary built environment, noise has emerged as one of the most pervasive and pressing issues across all building typologies. However, in recent times, an enhanced cognizance of the adverse impacts of noise pollution on human health has taken root. Specifically, within educational campuses, hostels, as the primary abode for most students, have been identified as sites where the assurance of indoor acoustic comfort is critical to bolster productive endeavors. However, the assessment of indoor acoustic comfort remains a less researched facet of indoor environmental quality. As a response to this knowledge lacuna, our research puts forth an innovative methodology that facilitates the assessment of the acoustic comfort of hostel buildings while meticulously analyzing the factors that impact the occupants' acoustic comfort. A case study hostel at the NIT Trichy campus has been selected, and two rooms from the same hostel block have been identified for further examination. The outdoor sound level is gauged at 2 meters from the facade, while the indoor sound level is assessed at the center of each room. Additionally, the reverberation time is measured in both rooms using the Bedrock SM 30 class -2 sound level meter. The collated data has been processed, and the results have been obtained. Furthermore, the methodology, as proposed by Project New TREND, has been employed to assign an acoustic class for each room. Room 1 has been categorized under class B, with a KPI of 4 points, while Room 2 has been allocated to class C, with a KPI of 3 points. This research posits a novel methodology that can enable designers to evaluate the acoustic class of hostels, which, in turn, can help them optimize facade elements to accentuate the indoor acoustic comfort.

Acoustics and the well-being of children and personnel in early childhood education and care

Studies implementing a multimethod perspective in evaluating the acoustics of early childhood education and care (ECEC) spaces both quantitatively and qualitatively are still scarce. In this study the acoustic environments (noise levels and reverberation times) of seven Finnish ECEC group’s premises were examined in association with personnel’s (N = 22) and children’s (N = 71) well-being. Personnel’s well-being and vocal health and children’s well-being were assessed with questionnaires. The findings were further elaborated by documentation of the ECEC spaces and semi-structured interviews with the ECEC personnel detailing their views on the acoustic environment of the daycare buildings and how and if the acoustics should be improved. The results showed that noise exceeding 70 dB affected personnel’s vocal health negatively, whereas no associations were found regarding acoustics and children’s or personnel’s well-being. Based on the interviews, sound spreading, poor insulation, and hard surfaces add to negative experiences of noisiness. ECEC groups need spaces that can be closed and acoustically separated from each other and from other groups. The possibility to close a space supports the perceived well-being of the users and provides a more varied and individualized use of the spaces.

The effect of furniture on room acoustic parameters and its dependence on different suspended ceilings' sound absorptive properties

In ordinary public rooms such as classrooms and offices, the base line of acoustical treatment is an absorbent suspended ceiling. Due to the non-uniform distribution of the absorptive material, the scattering as well as the absorption properties of furniture will have a significant influence on room acoustic parameters such as reverberation time, speech clarity and sound strength. In particular, the absorption of the sound scattered energy will depend on the absorbing efficiency of the suspended ceiling. This effect is not accounted for in classical diffuse field models such as Sabine's formula. Measurements were conducted in the reverberant room with varying degrees of furnishing for several ceiling treatments ranging from highly reflective to highly absorptive. Using Sabine's formula and the Statistical Energy Analysis model, this paper discusses the scattering effect of furniture on room acoustic parameters such as reverberation time, speech clarity and sound strength as well as how the equivalent scattering absorption area is related to the absorbing efficiency of the suspended ceiling. It is concluded that a novel method for the quantification of furniture is needed to include both absorption and scattering effects of furniture on reverberation time and its dependence on the suspended ceilings' absorptive properties.

Reverberation time measurement issues

The current ISO attempt to revise ISO 354 has ended in failure because the experts on the working group could not reach agreement in the required time frame. However, several important issues were identified. Some of these issues are discussed in this paper. The current ISO 354:2003 changed from using 30 dB of decay to using 20 dB of decay to determine the reverberation time. Unfortunately, the conversion of the theoretical formulae for the spatial and ensemble standard deviation from 30 dB to 20 dB of decay was not correct. The current version of the standard incorrectly changed the maximum linear averaging time and changed from specifying the maximum exponential averaging time to specifying the maximum exponential time constant but did not halve the maximum value. There is also evidence that the maximum exponential averaging time can be increased by 50% without biasing the measured reverberation time. When a discrete decay curve is analyzed, there are issues when deciding the first and last point to use when determining the reverberation time. During the attempted revision of the standard, it was proposed to specify a minimum amount of empty room sound absorption. This did not reduce the spread of results in the round robin and this paper gives theoretical results which suggest that this is to be expected.

Proposal of reverberation time to match the visual aspect of the architectural space displayed in VR using panoramic photographs

Most VR applications in the field of architecture are based on visual information only, and the addition of auditory information is expected to provide a more realistic representation. In order to provide a comfortable VR experience, discomfort due to inconsistencies between visual and auditory information should not occur. The aim of this study is to propose a reverberation time that matches the visual aspect of the architectural space displayed in VR using panoramic photographs. Subjective experiments were conducted on 15 virtual spaces created from panoramic photographs of architectural spaces to determine a reverberation time that matches the visual aspect of these spaces and to subjectively evaluate the visual impressions. Based on the results, several models of reverberation time to match the visual aspect of the architectural space displayed in VR using panoramic photographs were created. The results of this experiment showed that the model using the volume of the virtual spaces was appropriate.

Subjective and objective investigations on environmental properties to be displayed on sensory friendly maps at the Tokyo National Museum

Sensory friendly maps are known to be effective in providing advance information to visitors sensitive to environmental stimuli. However, the process of determining the environment al factors to be displayed on sensory friendly maps remains unclear. To provide visitors with useful advance information, we conducted a subjective evaluation and objective measurements, as a preliminary study, to create a sensory friendly map of the Tokyo National Museum. First, participants with autistic spectrum disorder were asked to explore the entire facility and record their perceptions at locations that they perceived to be characteristic. Second, objective measurements of the sound and lighting environments were conducted. Subsequently, the relationship between the subjective evaluation and objective measurements was assessed. Consequently, we discovered that some elements extracted through the subjective evaluation could be explained using objective measures such as the noise level, noise frequency characteristics, and reverberation time. Moreover, we confirmed that, in some cases, the subjective effect of sensory stimulation could change depending on the relationship with surrounding environments, purpose of the environmental setting, and qualitative factors. In such cases, adequate correspondences between the subjective and objective results could not be established.

The reduction of the reverberation using the sound-absorbing metamaterial in the conference rooms

Sound-absorbing metamaterial, iwasemi consists of multiple perforated Fabry-Perot resonators which have different resonant frequencies reciprocally to achieve broadband sound absorption coefficient. We have installed acoustic panels that are optimized for the main band of human voices, 1/3 octave band center frequencies from 500 Hz to 1000 Hz, in some conference rooms and measured the reverberation time of the rooms before and after installation. The measurement result shows that the acoustic panels have decreased the reverberation time of the rooms dynamically in the target frequency band (e.g. a case of we measured, the reverberation time reduced from 1.11 seconds to 0.66 seconds at 500 Hz octave band center frequency). As shown above, it has been indicated that installing plastic acoustic panels using acoustic metamaterial improves the acoustic environment in the rooms.

Assessment of Acoustic performance of classrooms in Ireland

In recent years the relationship between the quality of the acoustic characteristics of a learning space and the learning process has received increasing attention internationally. It is clear that poor acoustics in school classrooms make them unsuitable for learning tasks that involve listening. While we now know appropriate values for reverberation time and background noise in classrooms, limited studies have been conducted to assess the performance of Irish classrooms. This paper presents the results of a survey of the acoustic characteristics in primary school classrooms in Ireland, one of the first of its kind in Ireland. Reverberation times and background noise levels were measured in 30 classrooms, with the data collected used to assess compliance with standards set by the Irish Department of Education. Preliminary results suggest that approximately two-thirds of Irish classrooms fail to meet the required standard. The results of this survey highlight the need for improvements in the acoustic characteristics of primary school classrooms in Ireland.

Optimizing the shapes of concert halls through parametric design

Building acoustic simulation tools have often been used to ensure a room's acoustic performance, but they are rarely used in the early design stage. In this study, an acoustic simulation plug-in of Grasshopper for Rhino, Pachyderm, was combined with parametric design and a multi-objective optimization process to study the acoustic performance of a shoe-box-shaped concert hall in the early design stage. Three different factors of the sound field, sound pressure level A-weighting (SPL(A)), reverberation time (RT), and clarity 80 (C80), were discussed. One of the most famous shoe-box-shaped concert halls, Großer Musikvereinssaal, was selected as the comparison model. Two thousand results were generated through a multi-objective process in 36 hours. Compared with Großer Musikvereinssaal, the Pareto front of the 2000 results showed better performance in various factors of the sound field according to what it optimized.