Reverberation Time Research Articles

Exploring sound diffusion in learning environments through experimental and wave-based analysis

Acoustic design guidelines in learning environments generally involve specific requirements of reverberation time (T20), speech clarity (C50), and speech transmission index (STI) to ensure adequate quality for spoken communication. Predictive formulas recommended by international standards rely on ideal diffuse field theory as a crucial factor for meeting adequate room acoustics criteria. However, such theoretical assumptions are barely encountered in real-world rooms, undermining the predictions' accuracy. The present work explores the main factors influencing sound diffusion in classrooms by means of in-field acoustic measurements and numerical models. In detail, different desk configurations and the installation of materials with varying acoustic impedances at the suspended ceiling have been studied to evaluate the associated increase in sound diffusion. Among the several metrics to quantify sound diffusion, the standard deviation of measured reverberation time values has been selected in the present study. Experimental and simulated data findings reveal that the furniture layout with a single desk arrangement and the suspended ceiling's treatment with porous and perforated ceiling tiles increase sound diffusion by exploiting edge diffraction and material discontinuities, respectively.

Effect of sound absorption on noise reduction in the automotive industry

Industrial noise is one of the most common physical factors that cause annoyance and damage workers' health in the long term. Precautions should be taken to reduce noise and improve acoustic performance in industrial working environments. This paper aims to analyze the acoustic performance of the automotive industry and contribute to the global outcomes of sustainability and the development of strategies to improve the quality of the working environment through improvement scenarios. For this purpose, the automotive industry in Türkiye was examined as a case study. In-situ acoustic measurements were made in the seat manufacturing unit of an automotive factory and the current situation was transferred to the simulation program. The effects of acoustic improvements on A-weighted sound pressure level and reverberation time at mid-frequencies (500, 1000, 2000 Hz) were investigated through three different scenarios. In the investigations, noise distributions were carried out through noise mapping. The A-weighted sound pressure levels in the automotive industry were reduced by approximately 15 dB. As a result of the study, suggestions for noise control precautions and their effects on the automotive industry seat manufacturing unit are presented.

Operating room soundscape design intervention study

Noise levels in a typical Operating Room are often well beyond the recommended 45dB for a typical OR environment. Due to stringent cleanability requirements in hospitals, there are limited finishes that can be used in these rooms. Researchers from Gresham Smith and Siebein Acoustic are currently engaged in a research project to investigate how the design of the operating room environment can be acoustically optimized for staff well-being and better patient outcomes. . The study focuses on the environmental variables that can be controlled including the effects of diffusing panels, angling of the walls, and the use of special cleanable acoustic finishes on the ceiling in 3 prototypically sized Operating Rooms using 3-dimensional acoustic models. Acoustic metrics including Reverberation Time, Speech Transmission Index and clarity were compared for 11 scenarios. Results from the acoustical modeling showed that, comparing 11 different scenarios, rooms treated with absorption performed "best" on multiple metrics (Reverberation Time, Clarity, Speech Transmission Index/Intelligibility). Future research will be implemented within existing operating rooms of our hospital partner for in situ validation. Acoustical measurements will again be taken and evaluated against the initial findings and the perceptions of the users of the spaces.

SS 25268:2023, an acoustic standard for listeners and speakers

The sound environment in many classrooms is not good, and we know that poor room acoustics impedes learning and has a negative effect on teachers' voice health. Sound reflections in the room have a great impact on both speech intelligibility and speech comfort. SS 25268 is a Swedish sound standard for, among others, school buildings. The standard uses reverberation time, RT, to put requirement on room acoustics. There is a connection between the amount of sound absorption in the room and RT according to Sabine formula. The problem is that Sabine formula requires a diffuse sound field witch very seldom occurs in classrooms with acoustic ceilings. Another problem is when RT is evaluated with T20, the early reflections are not included, and early reflections have a great impact on speech intelligibility. The standard have been updated to a new version, SS 25268:2023. In this standard there is an opportunity for landlords to put other requirements then RT to evaluate the room acoustics. The standard have an appendix to help landlords, principals and teachers to better understand how to put the right acoustic requirements on their school buildings to create both good speech intelligibility and speech comfort.

Acoustic characterization of the Municipal Museum Abade Pedrosa

The 2016 interventions concerning the rehabilitation of the Municipal Museum Abade Pedrosa in Santo Tirso, Portugal were analyzed to verify in what way acoustics interferes in the museum enjoyment. In situ measurements were done in every exhibition room: Reverberation Time, RASTI and the Equivalent Sound Level (LAeq). RT[500, 1k, 2k Hz] values were between 2.5 and 3.9 s. The RASTI mean values varied between 0.44 and 0.55 s. LAeq values of background noise reached a top value of 43 dB(A) in the 1000 Hz frequency band and a global value of 57 dB(A) in every room. A multicriteria analysis was carried out to globally characterize the museum in a simple and perceptive way, with an algorithm that ranks all the different rooms, in which they were generally classified as "bad". A comparison of these values was done with similar studies in other museums: Soares dos Reis (Porto), Serralves (Porto) and other international museums, being possible to verify that the Municipal Museum Abade Pedrosa has worse acoustic values compared to those other museums. It was also suggested possible improvements that could contribute for the acoustic correction of the space, with a predictable cost of about 27000 €.

Consideration and case study using a time-difference-of-arrival directional device for occupational noise measurement

To protect worker's hearing in noisy workplaces, noise levels are measured periodically, and noise sources are located based on the results of recordings or video cameras. If the noise level is above a certain level, noise abatement measures are taken, or workers are suggested to wear hearing protection. Measuring the noise level can be done simply by placing a sound level meter on the floor, but finding the noise abatement is a time-consuming task. It is necessary to listen to the recordings one by one or review the video to find the noise abatement. We believe that a simple method of estimating noise abatement is very useful, since some noisy workplaces do not allow recordings or video cameras for privacy and confidentiality reasons. In this paper, noise source identification using a time-difference-of-arrival directional device in an indoor environment is examined. The results are analyzed in the context of room properties such as reverberation time, dimensions, and device localization. The paper also reports on practical use-cases in actual sites.

Optimization and adjustment of indoor acoustic environment of theatre - Taking Guangzhou design capital-design hall theatre as an example

Theater is a place for all kinds of performing arts, and its design and function are usually diversified to meet the needs of different types of performances. odeon software is calculated with the sound source method and sound line tracking method, and adopts the Lambert scattering algorithm to calculate the sound diffusion, so that the simulation process is more and more realistic, and the calculated results are closer to the actual measured values. using odeon software to simulate the Using ODEON software to simulate the Guangzhou Design Capital - Design Hall Theater, according to the simulation results, the reverberation time is relatively short and other issues such as corresponding adjustments and recommendations, to give the Guangzhou Design Capital - Design Hall Theater indoor sound-absorbing material layout plan.

Virtual assessment of phone booths' acoustic performance in laboratory and office environments

The irrelevant speech noise is one of the significant issues affecting workers' productivity and comfort. Acoustic furniture is the most common solution addressing this problem: mobile phone booths and partially closed workstations are two examples. The acoustic performance of such devices is defined with laboratory tests according to ISO 23351-1:2020. The sound power level measured in reverberation rooms with and without the product determines the reduction of speech A-weighted sound power level (DS,A). However, predicting acoustic performance in real-world scenarios is still challenging. The present work explores the discrepancies between DS,A, and apparent speech reduction (D'S,A) through numerical models. The study assesses the performance difference between a calibrated virtual reverberation room and virtual open-plan offices maintaining the same acoustic properties, i.e., sound transmission and sound absorption, of a typical two-person phone booth. Moreover, the study investigates the fluctuation on D'S,A changing main room acoustic criteria, e.g., the reverberation time (T) and the total absorption area (A). Results help define ray-based simulations' reliability in predicting furniture ensembles' acoustic performance.

Improvement of stage acoustics in a small circular-shaped recital hall

This paper investigates how stage acoustics can be improved by the installation of on-stage reflectors in a small recital hall with a circular floor plan. The target hall, which is designed as a second floor with a seating capacity of 533, has an average reverberation time of 1.31 seconds in the mid-frequency band at the audience seats when empty, and an average side reflection sound ratio of 0.4. The target hall, assessed as having a circular planar shape with wide left and right sides compared to its depth, is not conducive to performers. Therefore, we measured the stage acoustics according to ISO 3382-1, with a grid spacing of 1 m above the stage. We created a simulation model based on the measurement results. To enhance the stage acoustics, a movable reflector was placed on the stage, and the effective area of the stage surrounded by the reflector was varied and compared through simulation. The results indicated that as the effective area of the stage surrounded by the reflector decreased, STEarly improved. Meanwhile, in the audience, the installation of stage reflectors showed no significant difference in reverberation time or clarity, but the sound pressure level was slightly improved.

Determination of reverberation time in large educational auditoriums

According to the current regulation, acoustic comfort in educational buildings in Lithuania is ensured by applying sound insulation of structures and limiting excessive room reverberation. The maximum reverberation time values described in the document depend on the building's acoustic comfort class, room volume and frequency range. In order to determine the design values of the reverberation time for larger auditoriums, there is a need for consultations with an acoustic expert. This paper presents some typical examples of reverberation time measurements in new, old and modernized large lecture halls. The measurement results indicate good practice in the design and installation of new auditorium, as well as the nature and importance of acoustic problems in old and modernized ones. The analysis of the measurement results allows us to assume that the success of the project's acoustic quality often depends on the designer's ability to properly assess the design indicators and the properties of applied materials.

Realization of global audio telepresence via a learning-based model-matching approach with an acoustic array system

A Global Audio Telepresence (GOAT) system requires a microphone array to capture the spatial audio signals in the far end and a loudspeaker array to reconstruct the sound field in the near end. This seamlessly immerses near-end users in remote audio scenes with full ambience. In this paper, we use a learning-based GOAT system (L-GOAT) based on the model-matching principle, where a deep neural network (DNN) acts as non-linear filters for the GOAT system. The network training attempts to minimize the matching error between the signals reproduced by the DNN and the desired signals filtered by the far-end acoustic transfer functions (ATFs). Extensive simulations were carried out for multi-source scenarios in two different rooms with different reverberation times. To implement the L-GOAT system, a five-microphone linear array was adopted in the far-end room, while a six-loudspeaker array was utilized in the near-end room. The objective evaluation matrices, including the Perceptual Evaluation of Speech Quality (PESQ), Short-Time Objective Intelligibility (STOI), and the matching errors, were conducted to validate the efficacy of the GOAT systems. The proposed learning-based approach has demonstrated superior performance compared to a conventional digital signal processing (DSP)-based method.

A causal model for acoustic assessment of informal learning environments

Irrelevant and intelligible speeches are the most effective distractive noise sources in open-plan environments. They are inevitable in informal learning environments as group assignments are very common. Informal learning can be defined as any additional learning activity that takes place outside the classroom and is conducted individually and collaboratively on campus. This study will examine the impact of sound-absorbing materials on students' attention in informal learning environments in a causal manner. To examine the effect of materials, 3D models will be designed by changing the sound-absorbing materials, using reverberation time as a reference metric by applying the auralization process. The control and treatment models will be provided. The statistical significance of the impacts will be investigated using pairwise correlations, ANOVA, and multivariate regression methods.

Analyzing the impact of classroom design factors on acoustic comfort in higher education hybrid learning environments

The vitality of hybrid learning classrooms has escalated due to enabling factors including advancements in technology, the demand for flexible education, and responses to global crises. However, the inadequate preparation for implementing hybrid classrooms raises concerns about students' ability to understand speech due to a lack of attention to the importance of acoustic quality. As a result, this study aims to investigate the impact of classroom design factors, such as ceiling height, occupancy, and spatial layout configuration, on hybrid classroom acoustic performance. The field measurement data acquired from multiple classrooms was utilized for analysis. The impact of design factors on acoustic parameters, which comprise reverberation time (RT), speech transmission index (STI), and speech clarity (C50), was analyzed through simulation using ODEON room acoustic software. The simulation was conducted based on two distinctive categorizations, which were determined by the size of the classrooms. The outcomes revealed that the design factors consisting of ceiling height, occupancy level, and spatial layout arrangements influenced the acoustic performance at various microphones' locations in hybrid learning classrooms. Although the analysis effectively upholds students' learning experience and performance, it is valuable for designers and educational institutions to establish adequate acoustic qualities for hybrid learning environments.

Understanding the influence of impedance transitions of acoustically reflective vertical surfaces on the frequency-dependent effectiveness of absorptive ceilings in large non-Sabinian empty spaces

An unexpected phenomenon was observed during measurements of reverberation time in empty spaces to be fitted out, in which the only sound absorbing treatment consists of mineral fiber tiles on the ceiling, a material typically highly absorbing at mid and high frequencies during laboratory measurements: this involves a systematic increase of the reverberation time in octave bands between 1 kHz and 4 kHz in the measured empty spaces. The physical understanding of this surprising observation has focused on the question of the influence of impedance transition on sound scattering, and the influence of the frequency-dependent scattering properties of acoustically reflective vertical surfaces of different natures (glazing, plasterboard lining, masonry) of these empty spaces on the efficiency of a sound absorbing ceiling. These scattering phenomena were studied and modeled in a computer model in order to verify the model's adjustment hypothesis, an essential initial step before the study of the acoustic parameters in future fitted spaces and the effectiveness of acoustic solutions for space planning of open plane offices. Good consistency between the measurements and the empty model was observed when the frequency-dependent scattering behaviour of the vertical reflecting surfaces of different nature was taken into account in the simulation.

Fear free design guidelines: exploration of quantitative acoustic criteria

Fear Free(r) is an organization that is dedicated to changing the landscape of veterinary medicine by educating veterinary professionals, architects, engineers, and others about the importance of considering the psychological impact of the built environment on animals. By involving an interdisciplinary team of veterinarians, architects, animal behaviorists, and others, the Fear Free Hospital Design Guideline has been developed to inform the design of animal care facilities. In partnering with Siebein Acoustic, new quantitative criteria can potentially be included as part of the Fear Free Design Guideline. The first step in reducing noise within any animal care environment is prevention, reducing or eliminating the stressors that cause dogs to bark. Metrics for measuring acoustic control include Reverberation Time, alpha bar, STC ratings, requiring a Site Noise Study if located in a sensitive area, the use of OITC ratings for the exterior building skin and mechanical criteria for the specific space types that are typical of animal care facilities. These criteria have been drafted to provide quantitative performance criteria to complement the design efforts that Fear Free is undertaking to transform animal care environments into healthy, vibrant spaces that promote the well-being and safety of all occupants, animals and humans alike.

Optimization of speech intelligibility in street-facing rooms of adult care home based on acoustic simulation

Due to the limited availability of urban land in China, many adult care facilities have resorted to constructing roadside living spaces. However, this has led to a significant issue of traffic noise disturbance. Besides, many rooms lack of control over indoor reverberation. As a result, the communication efficiency of the residents might be greatly impacted. This study aims to investigate the impact of traffic noise level, room size, and surface sound absorption on speech transmission index (STI), based on a typical room layout and conducted using acoustic simulation. The simulation results indicated that in order to achieve the required STI over 0.79 for elderly residents, it is imperative to control the road noise interference below 40 dBA and ensure that the room reverberation time under 0.42 s. To achieve this, it is recommended that for a road with a noise emission level of 72 dBA, the distance between the roadside room and the road should not less than 10 m. Additionally, windows with Rw+Ctr over 28 dB without road sound barriers (over 20 dB with sound barriers) should be installed. Besides, the room area needs to be controlled within 20 m2 and an acoustic ceiling with NRC>0.65 should be installed.

Room acoustic survey of open and enclosed learning spaces in Finland

Use of open learning spaces for education has increased in schools while enclosed learning spaces are still used in most schools in overall. There is some debate that these two learning space types might differ in acoustic perceptions. If they do, room acoustic quality might be one explaining factor. Therefore, our purpose was to determine, whether these learning space types differ in room acoustic properties. We studied 10 schools with mostly enclosed and another 10 schools with open or flexible learning spaces in Finland. Altogether 73 learning spaces were investigated among the 20 schools. Measurements concerned reverberation time, Speech Transmission Index, and background noise level. Most of enclosed learning spaces (63%) met the new requirements of Finnish building regulations for enclosed learning spaces. Opposite to that, most of open learning spaces (91%) did not meet the regulations for open learning spaces. The results can be used in the root cause analysis of a teacher survey conducted in the same 20 schools. Teacher survey will be reported in another study. Parallel analysis of objective and subjective results is necessary to judge whether the current regulations are justified.

Selection of the averaging time for the interrupted noise method of measuring reverberation time

The author wrote the requirements for the selection of the averaging time for the interrupted noise method of measuring reverberation time in the international standard ISO 354:1985 "Acoustics-Measurement of sound absorption in a reverberation room". When this standard was revised to become ISO 354:2003, the evaluation range used to measure the reverberation time was changed from 30 dB to 20 dB. Because the working group which revised the standard did not know the reasons for the averaging time requirements, they incorrectly changed them to supposedly take account of the change to the evaluation range. The purpose of this paper is to give the reasons for the averaging time requirements so that they are corrected and not incorrectly changed again. It is necessary that the averaging time is not so large that information is discarded and so that, in the case of exponential averaging devices, the measured decay rate is not biased by the decay rate of the exponential averaging device. On the other hand, it is desirable that the averaging time be as large as possible so that the ensemble standard deviation of the measured reverberation times is as small as possible.

Effect of reverberation chamber volume on result of qualification procedure for loudspeaker and loudspeaker positions for airborne sound insulation measurements

Measurement of sound insulation from airborne sound is carried out by determining the level of sound power radiated by the test item. In laboratory practice, this translates into measuring the sound level in the transmitting and receiving chambers and measuring the reverberation time in the receiving chamber. When performing these measurements, significant fluctuations in the sound level for low frequencies can be observed, which is related to the occurrence of standing waves inside the chambers. To ensure proper level averaging, as well as repeatability and reproducibility of measurements ISO 10140-5 describes a qualification procedure for sources and source positions. This article presents the effect of increasing the volume of the source chamber on the results of the qualification procedure for sources and source positions for floor airborne sound insulation measurements.

Evaluating the effect of dome geometry on acoustical quality of a pavilion

Acoustic performance of structures is an emerging field of research enquiry, with limited number of studies conducted in the Indian context. To address this gap, this study examines the effect of varied dome geometry on the acoustic quality of a pavilion. In-situ measurements pertaining to energy decay curve from impulse sound were collated at a historical 'Baradari'. The square shaped pavilion considered in the study is surmounted by a shallow dome and has three doorways on each side. Virtual simulation models of the pavilion were built thereafter and validated. In this study, dome geometries that emerged between the 15th-19th century (corbelled, shallow, single-shell, bulbous, and onion) in the Indian subcontinent are examined. Acoustic simulation was conducted on treble software to assess and compare the sound quality of each dome geometry. The study found that the reverberation, RT30, for the flat dome was approximately half to that of the single-shell dome. The study established that the choice of dome geometry is crucial as it impacts the reverberation time. The study findings vary with building typology, size, and architectural features. Nevertheless, this study should be viewed as a case-specific analysis that identifies optimal dome geometry for improved pavilion acoustics.