Reverberation Time Research Articles

Robust 3D localization of anomalies in reverberation time measurements using the sound field scanning method

Reverberation time measurements form the basis for room acoustic optimizations of existing building structures. During the verification of the achieved room acoustic improvements, anomalies may appear in the reverberation time signal which may be hard to spatially localize, especially in spaces with demanding acoustic requirements such as large, open workspaces, or concert halls. This contribution focuses on the application of the Sound Field Scanning technology to the fast spatial localization of room reflections. In this process, an omnidirectional sound source is positioned at an observation point in the room and periodically excited with band-limited pulses. At the same observation point, an acoustic camera system consisting of a rotating linear microphone array is oriented towards the preferred spatial direction. The emitted pulses and associated room reflections are captured on the measurement surface of the rotating microphone array. Acoustic images with high depth resolution are generated in parallel planes to the measurement surface. In complex situations, the task of spatially localizing anomalies in the reverberation time signal can be reduced to a few measurements from different viewing angles, thus, significantly accelerating the problem-solving process with high confidence. The method is exemplarily described through the room acoustic analysis of a University Lecture Hall.

Increasing the accuracy of ISO 354 and ASTM C423 through modal identification

Measuring the acoustic properties of materials is a highly challenging task. Previous studies have highlighted errors in the absorption coefficient above 200 Hz, leading to absorption coefficient values higher than one. These errors are often attributed to differences in modal decays with and without the specimen. This effect is amplified in the case of highly reactive materials, such as innovative materials, that significantly impact the acoustic field and, consequently, the modal behaviour of the room. This work aims to reduce the difference between measured reverberation time values, with and without the specimen, through Data Augmentation. Modal identification was performed on measured impulse responses of porous specimens, where the alpha is known, allowing the determination of modal decay times and reverberation times within the frequency range of 70–180 Hz. A statistical analysis of natural modes and numeric solutions enables the identification of outliers. In this way, even in a non-well-optimized reverberation room, it is possible to enhance the accuracy of acoustic absorption measurements.

Comparing measured sound strength to theoretical sound strength for rooms of varying size

ISO Standard 23591 shows how the sound pressure level in a room can be estimated with the following two pieces of information: the sound power of sources in that room, and the sound strength G of that room as defined in ISO 3382-1. In an earlier study, the theory connecting room volume V, reverberation time T, and sound strength G was summarized, and a comparison of measured G to this theory was explored for a wide range of rooms. That test setup used Odeon software. In the present study, a different test setup is used implementing Dirac software to expand G testing to additional rooms of various sizes for evaluation under the same mathematical model. After a description of the equipment using Dirac software is discussed, a brief review of the additional rooms in which sound strength was measured is provided. Both measured and theoretical sound strength results are presented for these rooms. The difference between measured G and theoretical G using the mathematical model is analyzed statistically both for the Dirac test setup and compared to the results from the previous study.

Direction of arrival estimation in reverberant environments using a single vibration sensor on an elastic panel

The vibrational response of an elastic panel to an incoming acoustic pressure wave is dependent on the coupling between the incident angle and the panel’s bending modes. By examining the relative modal excitations recorded by a single structural vibration sensor affixed to the panel, the direction of arrival (DOA) of the incident wave may be inferred. In reverberant environments, determination of the DOA of a sound source is complicated by acoustic reflections. Panel microphones may be particularly susceptible to this effect due to their large surface areas and finite modal decay times. A study on the impact of reverberation on DOA estimation using panel microphones was conducted. The panel’s response to wake word utterances was recorded in eight spaces, with reverberation times (RT60s) ranging from 0.27 to 3.00 s. These responses were used to train neural networks for DOA estimation. Results indicate an inverse relationship between RT60 and DOA estimation reliability. Within ±5°, DOA estimation reliability was measured at 95% in the least reverberant space and decreased to 78% in the most reverberant space. Results also suggest that DOA estimation using panel microphones can adapt to diverse acoustic environments by training the system with data from multiple spaces with different RT60s.

Towards a better understanding of multimodal integration and sensorimotor adaptation to audiovisual environmental incongruence using Virtual Reality

People use previous knowledge and in situ judgment to produce speech with a vocal effort appropriate to a given environment’s acoustics. To test how people integrate auditory and visual cues in speech production, we employed a three-by-three cross-conditional audiovisual match-mismatch paradigm. Three visually distinct environments with three different room acoustics were selected: a gymnasium, a classroom, and a hemi-anechoic room. The visual environment was presented with a Virtual Reality (VR) headset and the auditory environment was a diffuse room impression, playing back the participants’ speech through loudspeakers in the room with different reverberation times. Participants were prompted to speak in all nine combinations of the audiovisual conditions, with three being congruent and six incongruent. Linear mixed-effects regression modeling was used to evaluate the effect of the audiovisual manipulations and time course on mean intensity. Preliminary results indicate that participants initially spoke at a level that matched the visual expectation and then adapted to the audio condition; detailed analysis of the time course of adaptation is ongoing and will be presented. This study furthers our understanding of multimodal integration and the sensorimotor adaptation of speech production, which finds applications in fields including communication in noise and VR soundscape design.

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.

Acoustics of two Hindu temples in southern India

Acoustically important aspects of Hindu worship include chants, bells, conch-shells, and gongs. Conch-shells and gongs are used at various times during puja rituals (Prasad and Rajavel, 2013), throughout which texts from the Vedas and other Sanskrit scriptures are chanted. These Vedic chants have phonetic characteristics such as pitch, duration, emphasis, and uniformity (Beck, 1995; Prasad, 2013). Traditional methods of acoustic characterization (e.g., for churches) are based on time domain characteristics like reverberation time and clarity. We term this as, “time domain soundscape of worship.” This is vastly different from Hindu worship which involves extensive use of bells, conch-shells, and gongs in puja rituals, all of which produce unique sonic characteristics making frequency of sound very crucial which we term, “frequency domain soundscape of worship.” Beck (1995, 2006, 2012) has explored the sonic aspects of Hindu tradition as they relate to the religion and drawn comparisons with religious practices in other cultures where pertinent. However, a comprehensive acoustic analysis of temples and the characteristics of these sounds within temples is yet to be done. In this paper, we analyze the impulse responses and decay curves measured at the Virupaksha and Vijaya Vittala temples in Southern India.

Understanding speech in everyday conditions—Effects of room acoustics and noise

Understanding speech in noisy, indoor settings is a considerable challenge for listeners. Room acoustics, such as reverberation and heating, ventilation, and air conditioning (HVAC) noise, all contribute to such challenges. In the current study, the effects of different backgrounds were examined in anechoic versus reverberant conditions at two different signal-to-noise ratios (SNRs) were examined. 60 monolingual American English listeners transcribed spoken English sentences under different noisy conditions. Overall, we tested two acoustic conditions: anechoic and reverberant, reverberation time = 1.5 s, with four speech conditions (target speech only, or combined with HVAC noise, two-talker babble, or both) and two different SNRs (0 dB and -3 dB). Both the target and babble speech were female voices speaking in English. Complex backgrounds resulted in decreased performance, and the detrimental effects of such masking were accentuated by reverberation and lower SNR. This study serves as a basis for future research exploring the effects of room acoustics on speech intelligibility to gain a more wholistic understanding of speech perception under realistic conditions.

Classroom architectural design evolution: Acoustic evaluation of public-school classrooms in Malaysia

Education transformation greatly emphasises curriculum modification to produce impactful future generations and yet often disregards the impact of classroom design in achieving desired education outcomes. The prioritisation of optimal acoustic quality in classroom design is crucial due to the inherent reliance on auditory abilities in the process of teaching and learning. Therefore, a comprehensive acoustic standard guideline for classrooms, ANSI Standard 12.60, was launched in 2002 and adopted for school classrooms in the USA. However, the scenario might be different in Malaysia, as there is no acoustic standard guideline established. Therefore, this study seeks to identify the actual acoustic conditions of classrooms that were constructed in the post-independence era. On-site acoustic measurements were performed to evaluate significant acoustic parameters, including reverberation time (RT), background noise level (BNL), speech transmission index (STI), and sound pressure level (SPL). The findings revealed that the RT for both classrooms was within the recommended value, while the BNL and STI of both classrooms failed to comply with the established recommended guidelines. In a similar vein, these findings translate the degree of awareness among the education institutions and construction sector of the importance of classroom acoustics in providing a better learning experience among students.

An analysis and retrofit of the acoustics at Image Creators Health and Beauty Salon

This paper discusses the analysis and retrofit of the acoustics in a high-volume beauty salon in Severna Park, Md. The major issues in what was intended to be a serene environment are reverberation times of 1–1.68 s in the mid-to upper frequency range and Background noise levels ranging from 73.4 to 64.6 dB in the mid to low frequency range. Employee and customer complaints include ear pain and tinnitus due to prolonged exposure to high background levels, heightened stress, vocal strain, headaches and poor speech intelligibility. Existing analysis and the acoustical retrofit resolution will be demonstrated.

Acoustic characteristics of bedrooms in two types of long-term care facilities in China

The aim of this study was to quantitatively determine the acoustic characteristics of bedrooms in two types of long-term care facilities in China. Objective acoustic conditions, including noise levels and reverberation times, were measured through a series of acoustic measurements in twelve bedrooms in two nursing homes and three adult care homes in Kunming city, China. The impacts of noise and sound preferences were evaluated through a questionnaire survey administered to residents and nursing staff. In terms of the sound field, the background noise levels in most measured bedrooms exceeded the WHO's recommended value (30 dBA) by approximately 10–15 dBA. Compared to those in adult care homes, the noise levels in nursing homes were approximately 5–7 dBA higher during the daytime and 2–3 dBA higher during the nighttime due to frequent nursing activities. Moreover, noise levels were 5–15 dBA higher in roadside bedrooms. The reverberation time of five bedrooms reached 0.8 s at low frequency (125 Hz) due to their large space and absence of sound-absorbing materials. The questionnaire showed that noise sources were mainly perceived as coming from corridors and out-of-windows by residents and nursing staff. Traffic noise, residents' yelling in pain (just in nursing homes) and footsteps were considered the most noticeable noises, which may have had negative effects on participants' sleep quality, health, and emotional state. Moreover, the residents in roadside bedrooms reported that noise had a greater impact on their sleep (p < 0.01). Compared to artificial and mechanical sounds, participants preferred nature sounds, such as streams and birds, which were significantly (p < 0.01) positively correlated with age.

Mechanical Fault Sound Source Localization Estimation in a Multisource Strong Reverberation Environment

Aiming at the sound source localization of mechanical faults in a strong reverberation scenario with multiple sound sources, this paper investigates a mechanical fault source localization method using the U-net deep convolutional neural network. The method utilizes the SRP-PHAT algorithm to calculate the response power spectra of the collected multichannel fault signals. Through the utilization of the U-net neural network, the response power spectra containing spurious peaks are transformed into “clean” estimated source distribution maps. By employing interpolation search, the estimated source distribution maps are processed to obtain location estimations for multiple fault sources. To validate the effectiveness of the proposed method, this paper constructs an experimental dataset using mechanical fault data from electromechanical equipment relays and conducts sound source localization experiments. The experimental results show that the U-net network under 0.2 s/0.5 s/0.7 s reverberation time can effectively eliminate spurious peak interference in the response power spectrum. As the signal-to-noise ratio decreases, it can still distinguish the sound sources with a distance of 0.2 m. In the context of multifault source localization, the method is capable of simultaneously locating the positions of four fault sources, with an average localization error of less than 0.02 m. The method in this paper effectively eliminates spurious peaks in the response power spectra under conditions of multisource strong reverberation. It accurately locates multiple mechanical fault sources, thereby significantly enhancing the efficiency of mechanical fault detection.

Directional reverberation time and the image source method for rectangular parallelepipedal rooms.

The image source (IS) method is a commonly used geometrical acoustics simulation technique in room and virtual acoustics. In particular, it has been used in the analysis of room reverberation under different choices of geometry and wall conditions. Under a simple rectangular parallelepipedal geometry, reverberation time is known to be dependent on the direction of arrival of reflections relative to the room axes. In this article, a closed-form expression for the directional energy decay and reverberation time is derived, which is valid in the late response, and may be used in the case of either angle-independent or angle-dependent reflection. The expression reduces to an easily evaluated formula in the case of an omnidirectional energy decay curve (EDC). Various numerical results are presented, including the validation of the closed-form expression against EDCs and late reverberation times drawn directly from the IS method.

The Effects of Signal to Noise Ratio, T60 , Wide-Dynamic Range Compression Speed, and Digital Noise Reduction in a Virtual Restaurant Setting.

Hearing aid processing in realistic listening environments is difficult to study effectively. Often the environment is unpredictable or unknown, such as in wearable aid trials with subjective report by the wearer. Some laboratory experiments create listening environments to exert tight experimental control, but those environments are often limited by physical space, a small number of sound sources, or room absorptive properties. Simulation techniques bridge this gap by providing greater experimental control over listening environments, effectively bringing aspects of the real-world into the laboratory. This project used simulation to study the effects of wide-dynamic range compression (WDRC) and digital noise reduction (DNR) on speech intelligibility in a reverberant environment with six spatialized competing talkers. The primary objective of this study was to determine the efficacy of WDRC and DNR in a complex listening environment using virtual auditory space techniques. Participants of greatest interest were listeners with hearing impairment. A group of listeners with clinically normal hearing was included to assess the effects of the simulation absent the complex effects of hearing loss. Virtual auditory space techniques were used to simulate a small restaurant listening environment with two different reverberation times (0.8 and 1.8 sec) in a range of signal to noise ratios (SNRs) (-8.5 to 11.5 dB SNR). Six spatialized competing talkers were included to further enhance realism. A hearing aid simulation was used to examine the degree to which speech intelligibility was affected by slow and fast WDRC in conjunction with the presence or absence of DNR. The WDRC and DNR settings were chosen to be reasonable estimates of hearing aids currently available to consumers. A WDRC × DNR × Hearing Status interaction was observed, such that DNR was beneficial for speech intelligibility when combined with fast WDRC speeds, but DNR was detrimental to speech intelligibility when WDRC speeds were slow. The pattern of the WDRC × DNR interaction was observed for both listener groups. Significant main effects of reverberation time and SNR were observed, indicating better performance with lower reverberation times and more positive SNR. DNR reduced low-amplitude noise before WDRC-amplified the low-intensity portions of the signal, negating one potential downside of fast WDRC and leading to an improvement in speech intelligibility in this simulation. These data suggest that, in some real-world environments that include both reverberation and noise, older listeners with hearing impairment may find speech to be more intelligible if DNR is activated when the hearing aid has fast compression time constants. Additional research is needed to determine the appropriate DNR strength and to confirm results in wearable hearing aids and a wider range of listening environments.

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

&lt;p&gt;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.&lt;/p&gt;

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 &gt; -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.