Room Acoustics Research Articles

Impact of Fee Free Education on Teaching Resources for Students with Special Needs in Public Primary Schools in Bukoba Municipality, Tanzania

This study sought to assess impact of fee free education on teaching resources for students with Special needsin special public primary schools in Bukoba municipality, Tanzania. Pragmatic paradigm was employed. Moreover, a mixed-methods approach was used supported by a convergent parallel design. A sample of 50 respondents (3 HTs and 47 normal teachers) was drawn using purposive and simple random sampling techniques from a population of 56 respondents. Questionnaires, observation, documentary reviews and interview were used to collect data. Descriptive statistics for quantitative data and thematic analysis for qualitative data were used as data analysis tools. The study found that, trained and specialised teachers for students with Special needs are inadequate. In regard to the state of instructional resources, findings show that, taped text books and computers with extended keyboards are available while overhead projectors and acoustic rooms were lacking. Concerning strategies adopted by the administration to encounter challenges in special schools, findings indicate that, the school administration involves various education stakeholders in strategic planning of school activities and in decision-making process, and establishes school generating projects. Based on the findings this paper recommends that, the local government authorities should maximise adequate instructional resources and specialised teachers. It is concluded that, trained and specialised teachers and instructional materials for students with Special needsare inadequate. Involvement of various education stakeholders in order to encounter challenges pertaining to these schools should be enhanced.

Reference Speech-recognition curves for a German monosyllabic test in noise: effects of loudspeaker configuration and room acoustics

Objective Measurement of reference speech-recognition curves for a specific speech test in typical clinical testing environments and for different loudspeaker configurations. Design Speech-recognition scores were measured at four signal-to-noise ratios for five loudspeaker configurations in two anechoic rooms, and in four audiometric test rooms with low reverberation times. Study sample 240 young participants (aged 18–25 years) without hearing impairment participated in the measurements. Results Reference speech-recognition curves for speech and noise from the front (S0N0) were similar across rooms. Compared to S0N0, lower speech-recognition thresholds (SRTs) were observed for all other loudspeaker configurations in which speech and noise were spatially separated. This spatial release from masking was significantly reduced for the audiometric test rooms compared to the anechoic rooms. A binaural speech-intelligibility model was used to verify the influence of room acoustic properties and loudspeaker configuration on SRT. Conclusions Speech-recognition curves for spatially separated loudspeaker configurations depend on the room acoustic properties, even in audiometric test rooms with low reverberation times. This makes it more difficult to compare clinical measurements with reference speech-recognition curves, or even with data measured in a different test room. It is thus recommended to document the loudspeaker configuration and test room for each clinical measurement.

Hierarchical meta-porous materials as sound absorbers

The absorption of sound has great significance in many scientific and engineering applications, from room acoustics to noise mitigation. In this context, porous materials have emerged as a viable solution towards high absorption performance and lightweight designs. However, their performance is somewhat limited in the low-frequency regime. Inspired by the concept of recursive patterns over multiple length scales, typical of many natural materials, here, we propose a hierarchical organization of multilayered porous media and investigate their performance in terms of sound absorption. Two types of designs are considered: a hierarchical periodic (HP) and a hierarchical gradient (HG). In both cases, it is found that in some frequency ranges the introduction of multiple levels of hierarchy simultaneously allows for: (i) an increase in the level of absorption compared with the corresponding bulk block of porous material (or to the previous hierarchical levels (HLs)), and (ii) a reduction in the quantity of porous material required. Another advantage of using this approach is on the fabrication, since only one porous material is required. The performances are examined for both normal and oblique incidences, as well as for different values of the static air-flow resistivity. The methodological approach is based on the transfer-matrix method, optimization algorithms such as the metaheuristic greedy randomized adaptive search procedure (GRASP), finite-element calculations and measurements performed in an impedance tube.

Acoustic Analysis of the Masjid at Necmettin Erbakan University Köyceğiz Campus in Konya

In this study, the passive acoustic performance of Necmettin Erbakan University Köyceğiz Campus Masjid was investigated. Designed as the largest masjid of the city with a capacity of 15,000 people and a volume of 43,200 m3, the masjid, which has traces of Seljuk, Ottoman and Modern architecture. is built as a complex at a location overlooking the city in the Meram District of Konya City, Turkiye. The aim of the study is to determine the acoustic comfort conditions by considering all the activities in the masjids as a whole. Within the scope of the study, the acoustic performance of the masjid was evaluated by determining different source and receiver points for each mode of activity. As a method, the chosen masjid was simulated with ODEON Room Acoustics Software Ver. 14.04 software. Objective room acoustic parameters were analysed in three groups. These are sound energy ratio parameters (reverberation time (RT), early decay time (EDT), clarity (C50, C80), lateral fraction (LF80)), speech intelligibility parameters (definition (D50), speech transmission index (STI)) and sound strength parameters (strength (G)). The results obtained were compared with precedent studies in the literature. In comparison with the acoustic values obtained in other masjid/mosque buildings, it was reported that, while the speech intelligibility of other masjids/mosques was at a satisfactory level, the masjid under consideration was at a poor level in both fully occupied and unoccupied conditions. In the analysis made for reverberation time, it was seen that the masjid discussed in this study showed similar characteristics to other masjids/mosques globally. As a result, it was determined that the dimensions of the surfaces forming the mihrab, the minbar design and the depths of the mahfil overhangs are effective regarding the acoustics of the masjid, and the design of curved surfaces should be carried out in a way that does not cause focusing problems. In addition, suggestions that can give guidelines to modern masjid designs have been put forward.

Data-driven room acoustic modeling via differentiable feedback delay networks with learnable delay lines

Over the past few decades, extensive research has been devoted to the design of artificial reverberation algorithms aimed at emulating the room acoustics of physical environments. Despite significant advancements, automatic parameter tuning of delay-network models remains an open challenge. We introduce a novel method for finding the parameters of a feedback delay network (FDN) such that its output renders target attributes of a measured room impulse response. The proposed approach involves the implementation of a differentiable FDN with trainable delay lines, which, for the first time, allows us to simultaneously learn each and every delay-network parameter via backpropagation. The iterative optimization process seeks to minimize a perceptually motivated time-domain loss function incorporating differentiable terms accounting for energy decay and echo density. Through experimental validation, we show that the proposed method yields time-invariant frequency-independent FDNs capable of closely matching the desired acoustical characteristics and outperforms existing methods based on genetic algorithms and analytical FDN design.

Exploring the current landscape of open research software in room acoustics

Over the span of six decades, researchers have dedicated considerable efforts towards the development of computational methodologies for predicting room acoustics. These methodologies comprise the calculation of detailed impulse responses, frequency responses, and the prediction of quantities and indicators. The classification of these computational approaches continues to evolve, particularly with the recent integration of machine learning methods into the realm of room acoustics. Notably, the research software or code underpinning these advancements is not as readily accessible to the public as the results it has generated. This lack of accessibility has posed challenges to reproducibility and potentially impacted the overall quality of scientific endeavors as well as hampered collaboration, hindering the progress within the field. This study provides insights into the current state of open room acoustics research software, presenting quantitative developments over the years. It further explores the measurable impact of shared research software and offers an outlook on the prospective value of open research software in room acoustics.

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.

Exploring sauna impulse responses

Sauna is an important element of Finnish tradition and culture, and its properties and features deserve preservation and archiving. Additionally, extreme temperature and humidity in a sauna comprise a unique environment for researching room acoustics in unusual atmospheric conditions. In the present study, we publish a dataset of room impulse response (RIR) measurements of a sauna during the process of warming up and throwing water on the stove. We explore several features of the dataset, such as the impact of the temperature and humidity distributions on the time-of-arrival of reflections, the atmospheric absorption of sound, and spectral coloration of measured RIRs. The results of this research show the influence of environmental factors on RIRs and allow an insight into the distinct room acoustics of a sauna while heating up.

Towards validating the diffraction-enhanced image source method

Accurately simulating room acoustics between directional sources and receivers in reverberant environments can be challenging. Wave-based numerical models can be used at low frequencies, but at higher frequencies, the cost of solving these models is often too prohibitive to permit practical use. Geometrical models can be used to simulate sound fields in rooms at higher frequencies but with limited accuracy due to the inherent assumptions made when deriving the models. Therefore, there are ongoing efforts within the room acoustics community to improve the accuracy of geometrical models. Recently, an extension to the image source method called the diffraction-enhanced image source method, which uses spherical harmonic descriptions to include directional sources and receivers, has been proposed. The proposed method can be used to efficiently model sound fields in shoebox-shaped rooms with directional sources and receivers at high frequencies. In this paper, predictions of the proposed method are compared to data measured in a shoebox-shaped room. It is shown that the proposed method captures many of the pertinent features of the measured transfer functions and impulse responses.

Revision of Sabine's and Eyring's reverberation theories

Sabine's and Eyring's reverberation theories are still the most important theoretical frameworks for room acoustics. The important physical quantities derived from these theories are the average sound pressure level (sound energy density) and the reverberation time (sound energy decay). Eyring revised Sabine's theory to become the reverberation time zero in the perfect absorption condition. However, Eyring's theory has contradictions regarding the sound energy density in a steady state and the energy decay from the steady state. In this study, in order to resolve these contradictions, the theoretical framework for the consistent system is presented introducing the new concept of the average impulse response in a room, and the contradictions in the current room acoustic theory are clarified. Based on the theoretical framework, Sabine's reverberation theory is revised by a different way of Eyring's theory. The reverberation time of the revised theory is shorter than that of Sabine's theory and longer than that of Eyring's theory. Finally, ray-tracing computer simulations were performed to verify the revised theory. Results of sound ray tracing simulations were in better agreement with the values calculated using the revised theory rather than those calculated using Sabine's and Eyring's theories.

Compensation of staircase-induced boundary absorption errors in FDTD simulation

Finite-difference time-domain (FDTD) methods are popular for wave-based simulations because their regular grid enables highly efficient implementation, especially on parallel processing architectures. On the flip side, these methods exhibit errors caused by the staircase approximations that result when arbitrary boundary geometries are approximated on the fixed grid. Of particular concern in room acoustics is the staircasing of absorptive boundaries, as this has been shown to cause errors as large as 40% in computed reverberation times that do not reduce when the grid is refined. This paper analyses the effectiveness of a previously proposed compensation method that consists of modifying the admittance boundary conditions based on the staircased surface area. A theoretical analysis shows that for special boundary orientations the numerical reflection coefficient converges to the exact result at low frequencies. Numerical tests complement this analysis to show that the compensation yields accurate results at intermediate orientations as well. A spherical resonator case further demonstrates that a close match between numerically and analytically computed relaxation times is also obtained for curved boundaries.

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.

Assessing indoor and outdoor noise quality and associated health impacts at selected schools in Surat, India

An optimal ambient environment is crucial for healthy development, yet the excess of vehicles and inadequately planned educational infrastructures compromise cognitive growth in children. This study evaluates the impact of ambient noise on student cognition in five schools situated along city arterial and sub-arterial roads. A total of 717 students from grades 7, 8, 9, and 11 participated. Noise levels were measured in prevailing noisy conditions (PC) and controlled silence conditions (SC) within classrooms using the Kimo dB300 sound level meter. The observed differences in noise levels between PC and SC varied across grades, showing reductions of 4.7 ± 3.5 dB, 6.1 ± 0.7 dB, 6.7 ± 1.3 dB, and 4.4 ± 3.46 dB for grades 7, 8, 9, and 11, respectively. Statistical analyses revealed significant differences in the average noise levels under both conditions. Furthermore, cognitive task performance in PC and SC was significantly different, as evidenced by paired t-tests in tasks such as multiplication, word formation, reasoning, and sentence construction. Dimension reduction techniques identified room acoustics, task difficulty, speech intelligibility, mental deficiency, and annoyance as critical factors affecting learning abilities. Teachers reported that major impacts of noise include annoyance, sleeplessness, headache, and hearing impairment.

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.

Adaptation and evaluation of Pyroomacoustics for auralization purposes

An open-source room simulation software that relies on geometrical acoustics - Pyroomacoustics - was used to compute Binaural Room Impulse Responses (BRIRs) of existing rooms that are modeled in the Benchmark for Room Acoustical Simulation (BRAS). Modifications were made to the software to investigate the impact of the scattering model on the acoustic parameter values. A comparison with the acoustic parameter measurements showed that the values of EDT, C80 and D50 were found to be closer when using the Vector-Mixing method in comparison with the original scattering method. Overall, the alternative method reduced by 95% the mean squared error on the acoustic parameter values. The sound source directivity was also considered in the simulations to quantify its influence on the perceived auditory scenes. A listening test was then conducted to compare binaural renderings derived from measured and simulated BRIRs. Results showed that ratings of the modified versions of the software were either not significantly different or significantly higher than those of the original version depending on the room and sound source. Including the source directivity significantly improved the perceptual ratings, which is thought to be due to the reduction of spectral and loudness differences with the measured reference.

Validation of an eigenvalue-based inverse method for estimating locally-reacting surface impedance

Accurate boundary condition descriptions are essential for creating accurate computational models for room acoustics. These descriptions are often defined in terms of absorption coefficients or surface impedances. However, obtaining complex-valued, frequency-dependent values for an acoustically absorbing material sample at low frequencies is a challenging task. In fact, the current measurement standard ISO 354:2003 does not provide a method for measuring absorption coefficients below 100 Hz. In this paper, a recently proposed eigenvalue-based inverse method for estimating locally-reacting impedance at measurement system resonance frequencies is validated. The validation uses data from three samples measured in an impedance tube. The method is also used to estimate complex-valued, frequency-dependent impedances at frequencies below 100 Hz in a measured reverberant room and in a simulated reverberation chamber.

Determination of a diffusion coefficient function for long rooms using a least square optimization approach

Over the last decades, considerable attention has been devoted to improving the diffusion equation model within the field of room acoustics. It has been found that this model is subject to certain limitations, with one constraint regarding the diffusion coefficient. The diffusion coefficient, a parameter integrated into the model, is a value that scales the sound intensity to the gradient of the sound energy density. Currently, this value is often treated as a constant, but research has shown that it is spatially dependent. This paper explores a method to optimise the diffusion coefficient for long rooms such as corridors and tunnels by comparing the results of the diffusion equation model with those computed with the radiosity model and using the least-square optimization method, minimising the difference between the results of both methods. The parameters of a diffusion coefficient function are optimised, targeting a function that can be applied to a range of elongated spaces.

The development of a new technical regulation on acoustics in buildings in Croatia

Even though Croatia gained its independence 32 years ago, up till now its legislation has not regulated the requirements that concern the acoustics in buildings. Instead, the regulations inherited from the former state of Yugoslavia were left in effect and have remained in use even after they were officially withdrawn, as no new regulations were adopted to replace them. To address this issue, a committee has been formed of experts affiliated with relevant governmental and professional organizations, and representing their respective fields of expertise, with the task of developing the new Technical Regulation on Acoustics in Buildings in Croatia. This document is to set detailed technical requirements on sound insulation as the means of protection from outdoor and indoor noise, the maximum permissible levels of indoor noise caused by service equipment, and the room acoustics design criteria for achieving optimal acoustics and/or as a noise reduction measure, to be partly or fully applied to a wide range of public and privately-owned buildings, with exceptions such as dedicated performance venues like concert halls or theatres. This paper presents the motivation for creating this document, its scope, and key aspects, as well as a brief overview of similar endeavors in the past.

Soundscape design methodology using a perception model for activity transition in future mobility

In the context of Future Mobility, a methodology for soundscape design using a perception model has been developed to facilitate the implementation of performance spaces among various activity transitions. This approach involved evaluating the soundscape and room acoustics of orchestra performances and solo singing that penetrate the vehicle interior, aimed at comparing with the auditory and visual environments of a concert hall. The performance hall being compared was a large, rectangular concert hall, and the evaluation point was located in the center of the audience. To investigate audio-visual preferences, variables related to sound pressure level and spatial acoustic quality were initially defined. Following this, in-car human perception in Concert Hall mode was assessed, grounded on indoor acoustic parameters relevant to music listening, encompassing acoustic satisfaction and audio-visual components. To enhance the poor audio-visual environmental conditions inside the vehicle from a UX perspective, implementations of transparent displays and stereoscopic sound were implemented. The methodology was validated based on the psychophysiological responses of participants to the audio-visual soundscape factors, aiming for performance enhancement.

Sound absorption coefficient in the audible and ultrasonic frequency range measured in a reverberation chamber with an omnidirectional parametric loudspeaker

An omnidirectional parametric loudspeaker (OPL) is a sound source that contains hundreds of ultrasonic transducers set on the surface of a sphere. Each transducer emits an ultrasonic collimated beam consisting of an audible exponential sweep sine (ESS) modulated in amplitude. This results in hundreds of ultrasonic sound waves emitted in all directions, but also audible sound waves generated by the parametric acoustic array (PAA) phenomenon, by which a modulated signal returns to the audible range thanks to nonlinear propagation in the air. This work examines how the OPL performs in assessing room acoustics, specifically in determining material sound absorption coefficients within reverberation chambers. The ISO 354 standard requires measuring reverberation times with the chamber empty and with the material sample. These are measured using ESS, which has proven effective for the OPL performance. This signal concentrates all the sound power into a single frequency, which improves ultrasonic power levels and thus the signal-to-noise ratio of the audible sound field. The absorption coefficient is next evaluated following the standard, and the results are compared with those obtained using a standard dodecahedral loudspeaker. Finally, the absorption coefficient in the ultrasonic range is examined to evaluate the OPL performance in this frequency range.