Acoustical Standards Research Articles

Functions for noise reduction in acoustic standards: evaluating reverberation time, mean absorption coefficient, and a novel approach

Contemporary European acoustic standards utilize dimensioning functions based on either reverberation time or mean absorption coefficient. For spaces with the primary goal of noise reduction, achieving consistent overall sound pressure level (SPL) reduction, regardless of room sizes and shapes is evidently desirable. The conditions under which reverberation time and mean absorption coefficient approaches align with the objective of consistent SPL reduction are analyzed. Generally, both approaches fall short of achieving consistency in case of varying ground surface or room shape, i.e. length, width and height relations. Additionally, in large rooms, constant or room height-dependent reverberation time functions may lead to extensive absorption areas, complicating the installation of acoustical treatments and degrading their economic efficiency. A novel dimensioning function, providing consistent SPL reduction independently of room size and shape, is derived based on diffuse field theory. The novel function is multiplied by a linear function of room height and length, to alleviate accuracy limitations of diffuse field theory in case of varying room shapes. Finally, simulations systematically varying room sizes and shapes demonstrate that the novel dimensioning function significantly outperforms existing approaches in achieving consistent SPL reduction.

Cross-comparison of the optical and acoustical calibration methods for microphones based on microelectromechanical system technologies

Calibration methods and associated international standards in airborne acoustics have enabled national metrology institutes to establish and maintain a fully defined traceability chain for designated laboratories and end users of microphones. However, such microphones need to be reciprocal, of condenser type and of specific dimensions; this, in effect, does not allow for the calibration of alternative existing sensor technologies and creates a further obstacle for the calibration of emerging technologies. An example relates to microphones based on microelectromechanical systems which are an integral part of a wide range of electronic devices; yet, there is no established calibration traceability chain other than methods employed by manufacturers. From a metrological perspective, new calibration methods that can accommodate microphones regardless of their size, reciprocal nature and utilised technology must be developed and subsequently standardised and adopted. This paper discusses the optical calibration method based on free field photon correlation and the acoustical calibration methods based on pressure comparison and free field substitution. These approaches can provide traceability to the international measurement standard system for novel types of microphones, and the measurement results showed themselves to be consistent. Based on this study, the possibility of expanding the new standard system was investigated.

Acoustic conditions in innovative learning environments

New generation or innovative learning environments are being developed in many OECD coun-tries, including Australia and New Zealand. These spaces are often criticized as being 'noisy', dis-tracting, unattenable, and yet, there has been a link between deep learning outcomes and the new generation environments. Education spaces primarily revolve around speaking and listening activities. Although new space typologies have been, and continue to be, developed, the acoustic standards applied to them are often the same as those applied to traditional cellular classroom spaces. This paper presents the results of systematic acoustic testing undertaken within numerous physical spaces for traditional and new generation learning environments in Australia and New Zealand, to compare the differences in performance between traditional cellular classrooms and open plan spaces, and summarise any trends evident in the information. It also acknowledges the differences between traditional cellular spaces and new generation environments as determined from the results.

Sound insulation characterisation of innovative natural ventilated façade in the context of living lab installations

Building acoustic standards like EN 14351 and ISO 10140 regulate the measurement of sound insulation of transparent elements, with indications of the test sample dimensions, test conditions, and criterions of adaptations of the results to different on-site conditions. However, given the research on innovative transparent building envelope including internal ventilation as double skin facades, these methodologies present limitations related to the characterization of the high variability of operating conditions in real in-field conditions. To this aim the acoustic performance could be explored with more flexible methods inside the multi-domain context of Living Labs, which present an opportunity for multiple characterizations and testing costs reduction. This work investigates the possibility of using the sound-intensity probe method to evaluate the airborne sound insulation of a transparent building element with internal ventilation. For this purpose, a comparative measurement campaign has been performed on the same building element installed in two Living Labs. The results show good compatibility between the different measurements and scales supporting the application of this methodology for comparative studies in the perspective of innovative building components measurements, and the application in Living Labs.

Acoustical Analysis of Auditorium in National Educational Museum, West Java

Abstract Besides being the place for evidence of past history and future history, the National Educational Museum in West Java also has audio visual room, for the visitor to learn about the museum more. Visitor ability to understand what is being said in the auditorium depends on the acoustics quality of the room. This study primarily talks about acoustics auditorium and find out if the acoustics in Auditorium of National Educational Museum is optimal for its function. The objective of this analysis is to determine the acoustics quality of the room in Auditorium of National Educational Museum. The simulation results with acoustic standards was carried out after conducting field observations and simulations using Ecotect v.5.50 software. After the simulation conducted it is known that there is some factors that makes this auditorium reverberation time not optimal such as sound-reflecting materials, floor and ceiling shape and elevation, and the number of occupants in the room. Which resulted in the speaker’s voice become less clear to the perceiver. Thus, to respond to the issue some materials can be change to sound-absorbing materials, and the ceiling shape can be made simpler to reduce the reverberation and echoes.

Perceptual consequences of reverberant environments on spatial unmasking

Spatial hearing provides access to auditory spatial cues that promote speech perception in noisy listening situations. However, reverberation degrades auditory spatial cues and limits listeners’ ability to utilize these cues for segregating target speech from competing babble. Hence, spatial unmasking—an intelligibility benefit from a spatial separation between a target and masker—is reduced in reverberant environments as compared to free field. To understand the perceptual consequences of poorer spatial unmasking in reverberation, we assessed three aspects of functional spatial hearing in virtual reverberant environments: perceived auditory source width, auditory spatial acuity, and spatial unmasking. Three auditory environments were simulated and auralized using ODEON to vary interaural coherence (IC): (1) a control anechoic environment, (2) a classroom designed to meet classroom acoustics standards (IC = 0.58), and (3) a classroom of the same size with more severe reverberation (IC = 0.37). Individually measured head-related transfer functions were used to binaurally reproduce the auralized signals over headphones. We hypothesize that interaural decorrelation, the result of increasing reverberation, will broaden the perceived auditory source width with a cascading effect of reduced auditory spatial acuity and subsequently poorer spatial unmasking. Preliminary data from normal-hearing adults will be presented. [Work supported by NIH R21DC020532.]

Determination of the Sound Absorption Area Inside an Elementary Classroom Using Three Acoustical Methods: Computer Modeling, 1/10-Scale Model Experiment, and Field Acoustic Measurement

Acoustic standards for classrooms around the world are still being studied, but the placement of sound-absorbing materials to meet these standards is still unclear. The present study examined an appropriate location for applying sound-absorbing materials inside an elementary classroom to ensure speech intelligibility while meeting the RT criterion using three scientific experimental methods, namely, computer modeling, a 1/10-scale model, and field acoustic measurement. A sound-absorbing material was applied to the rear wall or ceiling, and the ceiling was further divided into front, center, and rear sections. The acoustic performance was predicted using a 3D computer model of a standardized classroom based on the location of the sound-absorbing material. Subsequently, a 1/10-scale model following the law of similarity was used to compare the acoustic performances based on the location of the sound-absorbing material. Finally, field measurements were performed in an actual classroom to verify the acoustic performance based on the location of the sound-absorbing material. The findings revealed that the sound-absorbing material was most effective when applied to the rear wall, followed by application at the center, front, and rear of the ceiling.

Measurement-based Auralisation to Predict Room Acoustics Quality of a Large Mosque with a Pyramid-Shaped Ceiling in Bandar Lampung

Acoustic standards in mosques are available, but most people have a lack of understanding of these measures. Auralisation is an audio technology that uses impulse responses, dry sounds and convolution software to create authentic auditory experiences. In Indonesia, objective room acoustic parameters are still unknown and the potential of auralisation is underexplored. The study aims to predict acoustic quality and people’s preference for auralisation in a pyramid-shaped ceiling using field measurements and subjective ratings. The methodology includes pre-survey, RIR measurement, dry sound recording, auralisation, and subjective surveys. Background noise, T30, D50, and C80 were measured, while auralised samples of lectures and Quran recitations were evaluated. Respondents’ preferences generally correlated with T30, especially D50 (47%) for lectures and C80 (44%) for Quran recitations. In conclusion, the study demonstrates the interplay between subjective preferences and objective measurements and suggests that these parameters can predict acoustic quality in pyramid-shaped dome mosques, paving the way for better design practices and improved listening experiences.

Noise-induced sleep disruption from wind turbines: scientific updates and acoustical standards.

Wind energy appears to place global environmental benefits against local human health, particularly sleep. The result is a significant challenge to wind-energy development for the achievement of large-scale alternative energy. Our purpose is to examine noise from wind turbines and its potential to disrupt sleep, to examine the human health literature addressing these concerns, and to provide insight into how developers and communities can employ these concepts to pursue wind energy without impacting human health. The latest and most rigorous research on noise from wind turbines points to healthy sleep, when turbines are sited reasonably. This includes audible noise, low-frequency noise, and infrasound. Recent advances in acoustical standards provide practical methods to ensure adherence to these scientific findings. There now exist key data concerning wind-turbine noise, and its impact on sleep. Knowing that information, and how to deploy it with modern engineering standards should simultaneously facilitate wind development and protect human health.

Sphygmomanometer Dynamic Pressure Measurement Using a Condenser Microphone.

There is a worldwide need to improve blood pressure (BP) measurement error in order to correctly diagnose hypertension. Cardiovascular diseases cause 17.9 million deaths annually and are a substantial monetary strain on healthcare. The current measurement uncertainty of 3 mmHg should be improved upon. Dynamic pressure measurement standards are lacking or non-existing. In this study we propose a novel method of measuring air pressure inside the sphygmomanometer tubing during BP measurement using a condenser microphone. We designed, built, and tested a system that uses a radiofrequency (RF) modulation method to convert changes in capacitance of a condenser microphone into pressure signals. We tested the RF microphone with a low-frequency (LF) sound source, BP simulator and using a piezoresistive pressure sensor as a reference. Necessary tests were conducted to assess the uncertainty budget of the system. The RF microphone prototype has a working frequency range from 0.5 Hz to 280 Hz in the pressure range from 0 to 300 mmHg. The total expanded uncertainty (k = 2, p = 95.5%) of the RF microphone was 4.32 mmHg. The proposed method could establish traceability of BP measuring devices to acoustic standards described in IEC 61094-2 and could also be used in forming dynamic BP standards.

Estimation methodology for three-dimensional acoustic modeling: Predicting surf noise soundscapes in coastal urban environments

This research develops an estimation methodology for coastal surf noise soundscapes for implementation in three-dimensional acoustic modeling to improve communication of acoustic design and for assessment with sustainability, wellness and acoustic standards. As sustainability standards include more parameters relating to soundscapes, it is becoming increasing important to develop methods of communicating acoustics to designers in the built environment. Three-dimensional acoustic modeling provides a graphical tool for designers to engage with and understand the impacts multidisciplinary engineering and design decisions have on the soundscape of different parts of a project. As a nation with many coastal urban environments, the view, scents and sounds are all marketing and wellness points for residential and commercial projects. The methodology includes consideration of typical software-agnostic three-dimensional modeling inputs, capabilities and graphical outputs as well as the primary variables that influence measurement and prediction of coastal surf noise in relation to the constant environmental noise. Coast surf noise measurements have been collected and undertaken as part of this work and the data within the method may be updated for most locally measured data. This research aims to enhance the demonstration of soundscapes, facilitating more informed decision-making fostering sustainable development in acoustics, engineering and design.

Classroom acoustics: A case study of the cost-benefit of retrofitted interventions

It is known that suitable classroom acoustics is important for effective teaching and learning. To this end, many countries have developed classroom acoustics standards. However, research shows that these standards are often not implemented. Research assessing the implementation of classroom acoustic standards internationally concludes that successful implementation is driven by mandatory standards that are part of the building codes and that the cost of compliance is a barrier. The study presented here explores the cost of upgrading classrooms to achieve a suitable reverberation time. The paper presents a case study in South Africa, where acoustic standards are generally not implemented and cost and know-how are barriers. The objective was to optimize the cost, acoustic benefit, and accessibility of acoustic interventions. Four adjacent similar classrooms were retrofitted with different sound-absorbing ceiling panels that cover a percentage of the ceiling area. The weighted sum model was used to assess the suitability of each intervention, taking into account the cost, acoustic benefit (in terms of reverberation time), and ease of access to materials. The case study demonstrates that a noticeable improvement in acoustic conditions can be achieved without significant cost and provides a basis for further research to develop simple standardized design recommendations.

Industry-academia collaboration to develop new building standards

Industry and academia must go hand-in-hand to progress science and knowledge. Often, academic solutions may not be the most optimal solution for the field where there may be a time/ equipment/ training restriction. For our work, we focused on improving the building acoustic standards—specifically the impact performance of floor-ceiling assemblies–through industry and academic collaboration. The research student at Michigan Technological University worked closely with Veneklasen Associates through their (non-profit) funding arm, as well as through summer internships to learn the existing limitations for impact performance field tests. The student used this knowledge to develop a test method with improved reproducibility while ensuring that the test is fast and minimal new training is required. The student now works with Veneklasen Associates after graduating to continue developing this test method.

Reflections on the scientific basis of building-related acoustic standards

As with standards in other indoor-environmental quality, standards play also an important role in building and room acoustics field. They are typically expected to a) represent the state of the art in the respective area and b) arbitrate if a building's design and construction meets the mandated requirements. It is thus important to ensure that the standards' mandates are indeed based on sound scientific evidence. Given their utility as a source of guidance for practitioners, the standards of course need not be conceived as scientific treatises. Nonetheless, the respect for and trust in the standardization bodies and the documents they issue is arguably proportional to the strength of their underlying scientific basis. Given this presupposition, the main intention of the present contribution is to examine, via the review of 19 European, American, and international standards in the domain of building and room acoustic, if they provide, either directly or indirectly, evidence with regard to the included requirements and mandates. The results of this review suggest that the majority of the selected acoustic standards provide sparse references to the evidentiary basis of their mandates. Nonetheless, there are also contrary instances, where standards engage, to some degree, the experimental evidence underlying their mandates. A case study of such an instance displays the potential for future developments in developing explicitly evidence-based standards.

Classroom acoustics: Bridging the gap between standards and application

Many countries have developed standards to regulate the acoustic conditions in classrooms. Most standards agree that the ideal ambient noise level should be between 30 and 40 dB, a reverberation time of 0.4 to 0.7 s, depending on the age and specific needs of the students and the type of activities taking place. Some standards include noise transmission levels to reduce unwanted noise transfer between adjacent spaces. Despite these standards, studies continue to show that many classrooms do not have acoustic qualities that are conducive to good learning outcomes. In most counties, the acoustic standards are not compulsory standards and good classroom acoustics is treated as a “nice to have” rather than as a key to good learning outcomes. This paper provides an overview of the classroom acoustics standards in several countries across the globe, considering how widely the standards are applied and identifying key concerns or gaps in implementation. The objective is to seek examples of successful implementation of standards, whether compulsory or voluntary, and to recommend mechanisms or interventions that could support the uptake and mainstreaming of good acoustic design for classrooms.

Speech perception and deaf and hard of hearing children in the classroom: A multidisciplinary effort in the United States to bring data and standards to architects, school districts, and into building codes

This presentation will discuss efforts by a multidisciplinary team to overcome the notable lack of progress in the United States in acoustic accommodations for deaf and hard of hearing children in the classroom. Data collected through research efforts by members of this team, and by others, demonstrate the benefits of appropriate acoustics for all children and especially those deaf and hard of hearing. These efforts have resulted in a voluntary standard in classroom acoustics specifically for deaf and hard of hearing children by the American National Standards Institute. This standard, however, is not reaching built classrooms. This team representing the fields of acoustics, architecture and audiology is using speech perception data and new computer simulations to increase awareness of the need for classroom acoustic standards in building codes to accommodate deaf and hard of hearing children.

Auraltypical acoustics? A critical review of key standards and practices

The concept of aural diversity was born out of awareness that there is a deeply embedded and intertwined, singular model of hearing at the core of the preponderance of acoustic standards and guidance, and hence practice (Drever 2015, 2017). This is exemplified with the prescription of the 'otologically normal' hearer derived equal loudness contours (ISO 226:2003), giving form to ubiquitous A-weighted decibel - the 'otologically normal' characterising the hearing of 18 to 25-year-olds, arguably the healthiest sub-group of society. This paper will critically review this assumption through reviewing the current set of acoustics standards in the UK. Crucially it will probe at some of the methods underpinning historic and foundational studies and concepts that are referenced in current standards, such as the reliance on WEIRD (Western, Educated, Industrialized, Rich, and Democratic societies) samples to stand in for the whole of the human population. (Henrich, Heine, Norenzayan 2010; Cobianchi & Rosas Pérez, 2021). Through interviews with acoustic professionals, the paper will then look at how this is carried through into practice and finally, discuss the consequences of slavishly following these models, which studies have shown (Drever 2017), results in distress, negative impact on health and well-being and societal exclusion for some.

Investigation of an engine order noise cancellation system in a super sports car

Today’s cars must meet ever-higher acoustic standards, and so, to avoid compromising vehicle dynamics, handling performance and fuel consumption, standard passive methods alone do not provide sufficient performance. Active control solutions can provide a potential solution to this challenge, particularly at low frequency and such systems have been investigated for application to small cars, SUVs and luxury vehicles. These vehicles are generally characterised by fairly slow dynamics and limited noise emission and, therefore, this paper explores the challenging application of active noise control to a two-seat super sports car equipped with a naturally aspirated engine. This work aims to track and then control sounds characterised by extremely rapid frequency variation rates, up to peaks of over 80 Hz/s, and high sound pressure levels. A multi-channel, multi-order FxLMS based control system has been implemented, which has been modified to optimise performance for this application by including both convergence gain and leakage scheduling, to achieve effective control at the driver’s and passenger’s ears. To evaluate the performance of the controller, its performance has been simulated when applied to measurements taken under several vehicle manoeuvres, ranging from conventional constant engine speed to very fast engine run-ups. From the presented results, it is shown that the system can obtain high levels of control during the manoeuvre set, with the controller reducing the overall sound pressure level by more than 10 dB at certain frequencies when analysing a single order, and it reduces the overall loudness by around 5% in all of the analysed cases.

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.

The use and application of pressure-based acoustical metrics adopted within the International Building Code

The 2021 International Building Code (IBC) includes pressure-based metrics as the field acoustical standards for conformance. These include normalized noise isolation class (NNIC) and normalized impact sound rating (NISR) (ASTM E336-20 and ASTM E1007-21, ASTM International; 2021 International Building Code, Section 1206, International Code Council). Pressure-based metrics were intentionally used in lieu of power based metrics. The authors here address why pressure-based metrics are more appropriate than power-based metrics for field verification, following from previous work [LoVerde and Dong, “Field impact insulation testing: Inadequacy of existing normalization methods and proposal for new ratings analogous to those for airborne noise reduction,” JASA 118, 638 (2005); LoVerde, Dong, and Rawlings, “Sound pressure-based ratings for evaluation of in situ sound isolation,” Denver (2022)]. Furthermore, the authors shall present the application of these metrics as they pertain to Building Code requirements. This paper will include and present code interpretation as it relates to sample size and evaluation for compliance as it relates to Building Code and sampling of systems for acceptance.