Room Reverberation Time Research Articles

A tool to calculate the reverberation time of rooms with uneven absorption distribution

The reverberation time in rectangular rooms with uneven distribution of absorbing elements and surfaces, for example suspended ceilings, lead to a non-diffuse sound field. This implies longer reverberation times than predicted by sabines or eyrings reverberation formula. To enable a correct prediction of the reverberation times in such rooms, the only possibility was to apply room acoustic simulations, which require high effort to model the room and to perform the simulation. In 2021, a prediction method was published by Zhou et. al. to calculate the reverberation time in such rooms much more precisely than using sabines or eyrings formula, without the need for a room acoustic simulation. This method has been transformed into an online calculation tool, named "reverberate". In this contribution the methodology will be quickly reviewed and the online tool will be presented.

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.

Measurement uncertainty of ISO CD 23351-2 - Preliminary results

The purpose of our study was to determine the measurement uncertainty of ISO CD 23351-2 draft standard. Two sub-studies were conducted. In study 1, an accuracy experiment was conducted where 7 participants tested in the same room (in situ) two different products (full enclosure and partial enclosure). In study 2, an experiment was conducted where a single participant tested two different products in several rooms varying in room volume and reverberation time. Study 1 yielded an in-situ reproducibility standard deviation of 0.80.9 dB. Study 2 yielded a between-site standard deviation of 0.7 dB. The small standard deviations suggest that the technical content should not be essentially changed in the next versions of the standard. The results could be considered in next version of the standard ISO DIS 23351-2.

Room influence on the acoustical footprint of a violin

Every violin has a unique acoustical footprint characterized by its sound transfer function (TF), and this study measures the influence of a room’s acoustical properties on that footprint. Using an omnidirectional microphone (centered, perpendicular, 20 cm from the bridge) and a force measurement hammer, we collect data across six rooms (having 0.5 to 2 s average reverberation times). After vibrationally isolating the violin and muting its strings, we tap the bridge’s upper left corner ten times and record 0.3 s audio files of each tap (48 kHz sampling rate). We estimate the TF by normalizing the sound pressure level data by the tap force measurement in frequency space. Analysis of TFs reveal variations due to violin angle. Between 250 and 1.5 k Hz, (frequency range containing the violin's characteristic A0, B1+, B1−, and transition hill modes), the average standard deviation within a 10-tap set on one day is 1 dB, and 2 dB across multiple days. Higher frequencies have more variation. Observations are not clearly tied to room size or reverberation time. The data suggest repeatable measurements of the characteristic violin modes in different acoustical environments are possible, though additional research across multiple days is necessary to confirm reproducibility.

Developing a virtual reality application for cultural heritage and room acoustics education

We tend to use visual factors, such as architectural styles, features, specific decorations, and historical contexts, to characterize cultural heritage. Sound is a transient, ethereal phenomenon that tends to be neglected in historical records. While photographs and drawings can preserve the visual aspect of a building or scene, documenting the sonic impact of the spaces is more complicated. Particularly, the historic places used for sonic activities, such as music halls, performance halls, and worship spaces, are essential to document and preserve the acoustic qualities. An immersive experience using virtual reality (VR) technology effectively promotes public awareness about cultural heritage's importance. It simulates the room acoustics using spatial audio technology. It also can make the VR environment interactive to manipulate architectural features that change the room acoustics such as room volume, finish materials, reverberation time, and sound barrier. The main goal of this paper is to develop a VR application that can be used as a template to create a VR environment where 3rd to 8th-grade students navigate and learn about the history and architectural features of cultural heritage and the basics of room acoustics using a Quest headset.

NOISE REDUCTION ON AIR DISTRIBUTION GRILLES USING 3D PRINTED INFILL STRUCTURES

The aim of this research is to reduce the noise level of air distribution grilles using 3D printed infill structures. The grilles are installed on a newly developed autonomous ventilation system, which is used for decentralised ventilation of e.g., school classrooms. Several supply and return grilles with functional gyroid and honeycomb shaped infill structures were created and subsequently printed on an FDM 3D printer. Based on measurements and analysis of the maximum sound pressure levels at different microphone positions around the system and at different airflows, the combination of grilles with the greatest noise reduction was selected. The research is complemented by other data such as spectral analysis of the noise, measurement of the airflow velocity through the grilles and measurement of the room reverberation time. Significant noise reduction was achieved by using the proposed grilles and further conclusions were drawn. 3D printing technology proved to be a very useful tool in this case.

Podcast recording room design considerations and best practices

Podcast recording and listening has seen significant growth over recent years and continues to expand. The spaces used to record podcasts include everything from small closets to more sophisticated recording studios. There are not presently any known acoustic standards aimed specifically at the design of podcast studios. This paper discusses the question of what is required acoustically for a room to function successfully as a space for podcast recording. This is accomplished by examining an assortment of Jaffe Holden podcast studio projects, as well as existing standards for similar room types. Design considerations include background noise targets, sound isolation systems and performance targets, and room finishes and reverberation time targets. This paper also includes a discussion of how podcast studio acoustic design targets should be selected to optimize the functionality without overdesigning a space.

A Psychological Evaluation Model of a Good Conversation in Knowledge Creative Activities by Multiple People

Japanese companies have been focusing on enhancing the knowledge creative activities of older office workers in recent years. In addition, the way of working in the office has been shifting from traditional divisional routine work to collaborative or creative work, and office spaces are becoming quieter, with an increasing number of extremely quiet spaces (noise level < 40 dB). A sound environment that is too quiet gives workers the impression that it is difficult to converse with others, because they are worried about what people around them may think. The appearance of the knowledge creative society in recent years has led to a desire for changes in the workplace environment to improve the productivity of intellectual activities. To realize a sound environment that encourages knowledge creative activities, study outcomes need to be accumulated. Therefore, to clarify what kind of sound environment would be appropriate for knowledge creative activities by multiple people, we conducted psychoacoustic experiments to examine the effects of sound pressure level (signal-to-noise ratio), type of sound, and reverberation time in conference rooms on the impression of a “good conversation”. In addition, we considered a causal model for the psychological evaluation of a “good conversation” by conducting a multiple regression analysis of psychological evaluations of the experimental participants. The results indicated that a sound environment considered too quiet for multiple people to have discussions about knowledge creative activities lowers the impression of a “good conversation”, whereas high levels of relaxation lead to the impression of a “good conversation”.

Field measurement of reverberation time and average absorption of one high-rise building room by road traffic noise penetrating facade

The facade insulation (FI) is one choice for Road traffic noise (RTN) at a high-rise accommodation building nearby a motor road. The weakness of FI is from window, so the window insulation (WI) is also a prioritized descriptor. ISO16283-3 states a field method to measure FI using RTN. However, in room acoustics, besides FI, reverberation time (RBT) or indoor average sound absorption (IASB) are another two un-ignorable descriptors. When the value of IASB is small, the indoor noise is not only contributed from penetrating façade RTN, but also supplemented by the residual sound from high reverberation field, weakening FI. As a parallel to ISO16283-3, this paper suggests an engineering method to measure RBT and IASB of one high-rise building room close to a motor road by penetrating façade RTN. It can supply a convenient tool for the field measurement of RBT and IASB with RTN. At the end, we made a field measurement of RBT, IASB, and WI at a hotel room nearby a viaduct in Hangzhou of China, assistant to adjust RBT or IASB and WI so as to improve the sound quality of the hotel. Further, the method can extend to the lines of rail, aviation, and shipping.

The Analysis of Room Acoustic Parameters of Karaoke Rooms in Surabaya

This research is performed to evaluate the acoustic parameter and noise of several karaoke rooms in Surabaya. The type of rooms can be classified into small rooms and large rooms. All the measurements were conducted at 12:00 to 16:00 GMT+7:00. Based on the measurement results, noise criteria (NC) values range between 45 and 50. These values are quite high if compared to standard NC value, i.e., 25. This statement is in accordance with the low values of noise reduction (NR) of evaluated rooms: walls with glass accessories (12 – 16.5 dBA); door gap (8 – 13.9 dBA); wall (10 – 18 dBA); and door hinge (6.9 – 9 dBA) in the frequency of 1000 Hz. Therefore, the low values of NR lead to NC value exceeds the recommended value. According to the observation and the analysis, we obtain there are some rooms using special doors that are very well to absorb noise. However, those doors still have a drawback because they are equipped with glass which has a low value of NR. The addition of glass to the doors reduces NR value. Moreover, the ranges of reverberation time of small rooms and large rooms are 0.3 – 0.4 s and 0.6 – 0.7 s, respectively. This difference range is caused by the volume of rooms. In addition, the speakers of all rooms are the same, i.e., woofer speakers. It could be understood from the sound spectrum that has a range of 100 – 500 Hz. Lastly, all the analyzed rooms have a high value of noise. The measurement results 94 d B A of L eq and 104.3 d B A of L max . Regarding the health regulation, the sound that has those intensities is harmful to the human hearing.

Predicting the reverberation time in rectangular rooms with non-uniform absorption distribution

This paper proposes a new approach for modelling and predicting the reverberation time in rectangular rooms with non-uniform absorption distribution. The model considers three separate decays for the three room dimensions and a fourth decay for the diffuse field. The sum of the four decays’ RMS-sound pressure values lead to a total decay curve, from which the reverberation time is obtained. Moreover, the model takes into account the absorption coefficients, empirical scattering coefficients at each room surface and lateral sound absorption from side walls. In rooms with a uniform absorption distribution, the calculated reverberation times are similar to those computed by the Eyring’s formula (C.F. Eyring: Reverberation Time in “Dead” Rooms. The Journal of the Acoustical Society of America Volume 1 (1930), p 168). In rooms with a non-uniform distribution, the modeled reverberation times are lengthened, consistent with measurements in previous studies over the whole frequency range. The paper discusses the comparison of calculation and measurement of decay curves and reverberation time, including other well-known simple prediction models.

Frequency-Dependence Characterization of Electromagnetic Reverberation in Indoor Scenarios Based on 1–40 GHz Channel Measurements

A novel model for the reverberation time is proposed in this letter, based on room electromagnetics theory. While the commonly used models consider absorption based on a constant rate of wall interactions within a given time, the proposed model takes the variance of interactions into account. Moreover, the frequency dependence of electromagnetic reverberation characteristics in indoor environments is experimentally investigated from 1 to 40 GHz. The reverberation time is found to be a decreasing function of frequency. A model is then developed to predict the room's quality factor, reverberation time, and average absorption coefficient. Good agreement is obtained with the limited results reported in the literature for similar scenarios. This approach aims to be an accurate alternative to the reverberation time measurements and computations in indoor environments by linking it to the theory of electromagnetic fields in cavities.

Detection of activity and position of speakers by using deep neural networks and acoustic data augmentation

The task of Speaker LOCalization (SLOC) has been the focus of numerous works in the research field, where SLOC is performed on pure speech data, requiring the presence of an Oracle Voice Activity Detection (VAD) algorithm. Nevertheless, this perfect working condition is not satisfied in a real world scenario, where employed VADs do commit errors. This work addresses this issue with an extensive analysis focusing on the relationship between several data-driven VAD and SLOC models, finally proposing a reliable framework for VAD and SLOC. The effectiveness of the approach here discussed is assessed against a multi-room scenario, which is close to a real-world environment. Furthermore, up to the authors’ best knowledge, only one contribution proposes a unique framework for VAD and SLOC acting in this addressed scenario; however, this solution does not rely on data-driven approaches.This work comes as an extension of the authors’ previous research addressing the VAD and SLOC tasks, by proposing numerous advancements to the original neural network architectures. In details, four different models based on convolutional neural networks (CNNs) are here tested, in order to easily highlight the advantages of the introduced novelties. In addition, two different CNN models go under study for SLOC. Furthermore, training of data-driven models is here improved through a specific data augmentation technique. During this procedure, the room impulse responses (RIRs) of two virtual rooms are generated from the knowledge of the room size, reverberation time and microphones and sources placement. Finally, the only other framework for simultaneous detection and localization in a multi-room scenario is here taken into account to fairly compare the proposed method.As result, the proposed method is more accurate than the baseline framework, and remarkable improvements are specially observed when the data augmentation techniques are applied for both the VAD and SLOC tasks.

Reverberation time and audibility in phased geometrical acoustics using plane or spherical wave reflection coefficients.

Room acoustics parameters are typically predicted using some form of geometrical acoustics for large rooms. For smaller rooms, phased geometrical acoustics improves results for lower frequencies. The use of a spherical wave reflection coefficient improves the results further, yet the exact impact on room acoustics parameters is not fully known. This work predicts the reverberation time in medium-sized rooms (27 m3 < V < 300 m3) using phased geometrical acoustics. The difference between the use of plane and spherical wave reflection modeling is analyzed for a variety of boundary conditions, including non-uniform distribution of absorption. Since calculated differences are greater than the conventional just-noticeable-difference of 5% for reverberation time, laboratory listening tests are performed to confirm audibility of the modeled differences. Two narrow band noise stimuli (octave bands with central frequency 125 and 250 Hz) with a duration of 1 s were used for comparisons of 18 acoustic scenarios by means of a three-alternative forced choice method. More than half of the listeners could hear the differences in all 36 cases. Statistically significant results (chi-squared test was used) were found in two-thirds of the cases, corresponding to those with longer reverberation times.

Multiple-Layer Microperforated Panels as Sound Absorbers in Buildings: A Review

Sound absorbing materials are used in buildings to dissipate sound energy into heat using viscous and thermal processes. Sound absorbers increase the transmission loss of walls, decrease the reverberation time of rooms, and attenuate the noise generated by internal sound sources. Porous absorbers (fibrous, cellular, or granular) are the most used materials in noise control applications because of their high performance-to-cost ratio in the frequency band of interest. However, when cleaning conditions and health reasons are of concern, microperforated panel (MPP) absorbers may be the preferred choice. MPPs, consisting of many minute (sub-millimetric) holes in a panel, are tunable absorbers in a prescribed frequency band, whose main shortcomings are high manufacturing cost and limited absorption frequency band. Currently, the production cost of MPPs can be drastically reduced by means of modern techniques. The absorption frequency band can be considerably enlarged by designing multiple-layer MPPs (ML-MPPs). The aim of this article is to review the high potential of ML-MPPs as a modern, clean, and healthy alternative to porous materials for sound absorption.

The influence of the distribution of sound absorbing materials on the estimation of reverberation time in rooms

Reverberation time in rooms depends on many factors, e.g. cubature, surface of envelopes, sound absorption coefficient of materials used for the construction of the envelopes, geometry of rooms or the distribution of sound absorbing materials. The arrangement of sound absorbing materials in rooms has an impact on the dispersion of acoustic field, yet theoretical calculation models do not take into account this impact. According to these models, regardless of the arrangement of sound absorbing materials, the reverberation time in a room will remain unchanged. The present paper investigates the above problem by means of computer simulations. For the needs of the simulation, three rooms with different dimensions were adopted, i.e. type 'p' - a cuboidal room with a square base, type 'd' - a cuboidal room (with one side of the 'p' room lengthened), type 'w' - a cuboidal room (with the height of the room lengthened 'p'). During the simulation, the way of acoustic field dispersion was being changed and its influence on the reverberation time in the rooms was being determined. The authors investigated two situations. The first one involved a non-dampened room, in which the sound absorbing material was being arranged differently. The second one involved a welldampened room, and the dispersion of sound field was analyzed depending on the location of the reflecting material.

Voice production effects due to extreme reverberation times in real rooms

Public school teachers have a heightened risk of voice problems. There are many potential causes of this increased vocal risk, including poor room acoustics (e.g., excessively high or low reverberation times). With increased understanding, rooms could be better designed to maintain communication transfer (intelligibility), while mitigating unhealthy vocal effort and, by extension, voice problems. The present study quantified the influence of a wide range of reverberation times (RT20) on vocal production parameters. Thirty-two participants were recorded completing a battery of speech tasks in eight widely ranging conditions within a reverberation chamber. Changes in RT20 had highly correlated effects on several vocal parameters, including smoothed cepstral peak prominence, acoustic vocal quality index (AVQI), and pitch strength. As RT20 increased, vocal parameters tended toward values commonly associated with dysphonic phonation. Additionally, results were gender dependent, with females tending to produce voice with higher vocal effort than males. These findings begin to objectify the effects of room acoustics on vocal accommodations and provide grounds for developing future talker-oriented room acoustical standards.

The relationship between floor vibration from an underground source and the airborne sound pressure level in the room

ABSTRACTPrediction, measurement, and assessment of groundborne noise in buildings due to the operation of underground railways frequently involves knowledge of floor vibration and requires a calculation to be made to estimate the airborne sound pressure level that will be caused by the floor vibration. A rule-of-thumb conversion between the vertical velocity level and the airborne sound level is frequently made. Approximations using calculations of radiation efficiency of the floor plate and the room reverberation time are also sometimes made. This article reviews the classical equations for coupling between finite plates and rectangular rooms using wave acoustics, and their application to floor plates in buildings at low frequencies. It also compares calculated relationships between floor velocity and the room sound pressure level with numerically modelled sound pressure in the airspace above a vibrating plate. Conclusions are drawn regarding appropriate ways of assessing airborne noise caused by a vibrating floor plate when only the floor vibration is known.

Investigation Studies on the Application of Reverberation Time

AbstractThe paper presents the research studies carried out on the reverberation time of rooms, in terms of theoretical aspects and applicability potentials. Over the last century a very large number of scientists have been attempting to work out models describing the reverberation time in enclosed rooms. They have also been trying to apply these models for the description of various acoustic parameters of the interior, i.e. the intelligibility of speech, clarity, articulation, etc. In fact, all these models are based on the Sabine’s statistical method. The paper presents the work of the scientists working on this problem, together with prospective applicability potentials. Such a review may be helpful for researchers, designers or architects involved in the discussed subject.

The Same Reverberation Time in Two Identical Rooms does not Necessarily Mean the Same Levels of Speech Clarity and Sound Levels when We Look at Impact of different Ceiling and Wall Absorbers

For setting the acoustic conditions in a classroom for teaching and learning activities, it is common to only measure Reverberation Time (RT). To calculate the RT in rooms with ceiling absorption is common but this data can also be misleading. Indeed, we measured the similar RT values in two identical rooms with different acoustic treatment, even though the calculations predicted significant differences and interestingly the rooms are also be perceive quite differently in reality.Taking the human response to sound into account the measured RT data alone leaves us in the dark when seeking to explain the difference in human user perception. Measuring additional room acoustic parameters such as speech clarity and the difference in sound levels, identifies other important differences between the two unoccupied but furnished rooms with the same RT and points to why only one of the two rooms seems fit for purpose as a group activity room.We will discuss how to achieve room acoustic comfort in classrooms; short RT, low sound levels and high speech clarity. In addition to commonly accepted short RT values we will discuss recommended objective values for good Speech Clarity to support good speech communication activities in typical teaching and learning rooms in real life situations.