Noise Sources Research Articles

Measurements of noise emissions for classification of highway expansion joints

In this paper, we classify expansion joints on Slovenian highways by their potential as noise sources. To measure this potential, we utilized a close proximity measurement chain with additional vibration measurements on the car's undercarriage. By combining these measurements, we were able to amass a large amount of noise relatable data specific to expansion joints. By correlating this data to expansion joint types present on a number of bridges and viaducts, we were able to statistically analyse and rank various joint types regarding their noise emission. Our previous research activities focused on noise complaints associated with specific cases that showed that the problem can be very annoying, even though it was quite localized. Our study opens up a new way to assess expansion joints during regular close proximity measurements on the road network, and simultaneously presents a quantifiable measurement data basis to exhibit the expansion joint noise emission problems near highways.

Application of a novel visual representation method for urban noise source monitoring

Increasing urban mobility has led to a rise in the number of vehicles, resulting in urban noise pollution, which can cause health problems. Conventional methods for noise control can be adopted to reduce noise near the sources. However, this is not cost-effective to reduce overall noise level in the urban area. Therefore, it is preferable to encourage drivers to voluntarily reduce noise by applying methods such as cracking down on road noise sources. To this end, a real-time urban noise source monitoring system is needed, but processing large amounts of data can be difficult. In this study, a novel visual representation method, DoAgram, is applied for urban noise source monitoring. DoAgram can represent the time, frequency, and spatial information of the sound source within a 2D color graph. Therefore, the long-term spatial information of the sound source acquired from the sensor array node can be transmitted as a single image. Also, one can restore spatial information of the source from an image through a decoding process corresponding to the encoding method. One can find that the proposed method can be utilized as a database that can efficiently conduct urban noise source monitoring.

The LIFE SILENT project's approach to sustainable noise mitigation

The main objective of the LIFE SILENT PROJECT is the development of sustainable and eco-friendly solutions to mitigate noise in complex urban environments, where multiple and diverse noise sources, mainly roads and railways, coexist across densely populated areas. Mitigating noise in such environments generally excludes the use of solutions that might interfere with the urban context, such as noise barriers. This is mainly due to the proximity of receivers to the noise source, which reduces the visibility of the surroundings and air circulation, leading to microclimatic modifications and social opposition. This is why noise mitigation measures acting directly on the source are recommended, such as low-noise pavements for roads, and dampers, rail grinding, and silent brakes for railways. However, these solutions suffer from either durability issues or high implementation costs. Thus, an improvement is necessary. In the LIFE SILENT project, innovative and sustainable low-noise and long-lasting pavements, as well as low-height noise barriers will be developed and demonstrated in a real test environment. Additionally, procedures will be established to facilitate their synergistic implementation, providing transport infrastructure owners and managers with solid information to support their widespread adoption. In this paper, a general overview of the LIFE SILENT project is given.

The ocean wave noise masking effect on wind turbine noise audibility

In Denmark and several other countries noise is regulated as absolute levels, hence the audibility of the noise source is not directly handled. In most countries, including Denmark, wind turbines are often set up in rural areas. Denmark is a flat, windy and in general densely populated country, but the rural areas are less populated and has longer distances between dwellings, and so it is easier to comply with the setback distances and noise demands. Coincidently some of the windiest parts of Denmark are also rural areas. In the rural areas some of the common sources of noise is vegetation or waves, which masks other environmental noise sources. The effect of masking from vegetation and/or waves has not been studied in much detail in Denmark. The aim of this article is to gather meteorological, wave and sound data from waves at the Danish west coast and compare this data to estimated offshore wind turbine noise.

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

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

A sound recognition algorithm to filter non construction site noise

Sixense Engineering have developed a new algorithm to correct the noise levels measured around construction sites, by identifying and filtering out sounds that are generated by activities outside the site (emergency services sirens, traffic horns, etc.). The idea is to go beyond the simple classification of audio files by applying the classification algorithm to all the noise events that contribute to the noise dose LAeq,T. In this innovative process, the noise dose is calculated from elementary LAeq,1min,. When noise events are detected (in terms of LAeq,1min), the corresponding audio recording (.wav file) are analysed by the sound recognition algorithm. When the algorithm identifies that the noise source is not construction related, with a high degree of confidence, the corresponding LAeq,1min is excluded from the noise dose calculation. In other words, the measured noise dose can be filtered by removing non construction related noise events produced by external sources like sirens, horns, motorbikes, birds, music, etc.

Accounting for the vehicle influence on tyre noise through acoustic simulation based on equivalent monopole sources

Road traffic noise poses a risk to human health and amongst the different noise sources, tyre-road interaction plays a fundamental role. Due to the regulations introduced to limit noise levels, tyre manufacturers are committed to design acoustically optimized tyres. In this context, a numerical-experimental approach for including vehicle influence on tyre noise has been investigated. As a first step, equivalent monopole sources are identified based on the measurements of the radiated sound field of a rolling tyre in a semi-anechoic chamber. In a second step, the same sound sources are then employed for the prediction of sound propagation when tyres are mounted on a vehicle, which is included in the acoustic simulation. Finally, a validation against indoor experimental measurements is performed, yielding promising results.

Advancing noise reduction strategies for domestic air-source heat pumps

With the increasing adoption of heat pump technology in the energy sector, addressing noise emissions is crucial for public acceptance, regulatory compliance, and sustainable urban planning. Air-Source Heat Pump's noise emission, noise sources, reduction strategies, problematic frequency ranges, and noise transmission within buildings are considered. Various noise reduction strategies, including the strategic siting, enclosures, and vibration isolation techniques, are discussed. This study considered a scenario of heat pump noise emission which generated noise complaints. The heat pump noise source is investigated though 24 hour monitoring of far field acoustics in a suburban residence. A commercial implementation of ISO 9613 is used to predict the environmental noise impact. Results demonstrated that levels exceeded natural background by as much as 10-15 dB but that this could be mitigated through strategic placement of the heat pump. This study underscores the importance of implementing comprehensive noise control strategies for Air-Source Heat Pumps in urban areas to safeguard community well-being and ensure regulatory compliance. By integrating innovative noise reduction technologies and considering factors such as strategic location of Air-Source Heat Pump, installation practices, building design, and proper urban planning policies can enhance Air-Source Heat Pump's reliability while promoting a sustainable urban development.

Advancements in railway noise simulation: assessment of tools for virtual validation

In pursuit of more efficient and cost-effective measurement campaigns, the railway industry is embracing the prospect of virtual validation based on simulations. The primary obstacle lies in the need for noise simulation tools capable of accurately replicating complex sources, installation effects, noise propagation, ground reflection and, for some cases, the diffraction in the different train surfaces. This paper presents insights derived from European project Shift2Rail S2R-CFM-CCA-01-2019 Energy and Noise & Vibration WP6, concentrating on the validation and enhancement of two exterior noise simulation tools, tailored for railway applications. The paper covers four reference cases, simulating exterior noise at standstill with diverse noise sources and varying source locations and noise emission (i.e. electrical noise, cooling, etc.). A correlation with previously conducted measurements at typical receiver locations (7.5 meters from the track centerline) is carried out. The measurements were conducted in a "controlled" configuration, isolating as much as possible the analyzed noise source and gathering all the needed information about the ground and train geometry. The evaluation between measurements and simulations is done against a global and a 1/3rd octave band criteria with successful results. Finally, key features essential for achieving more accurate simulations are listed.

Sound prediction of an electric car using numerical simulation and sound synthesis techniques

The automotive industry's transition to electrification raises new challenges to maintain a comfortable acoustics environment both inside and outside the car. This paper presents an innovative way to make an early prediction of the overall sound of a vehicle at driver's ear by mixing noise sources that can be simulated and noise sources measured at component level. This hybrid approach combining Test and Simulation data helps define acoustic and vibration specifications at component level and take decisions on design strategies. For instance, the mounting method of the Electric motor to the body can be decided using a combination of Electric motor numerical simulation and Rolling noise sound synthesis techniques. Realistic signals could be generated and compared with sound quality metrics to choose the best vibration isolation strategy.

Generalization of noise insulation afforded by common window designs with active noise control exposed to moving noise source

A window device that can provide noise insulation while maintaining natural ventilation is highly desirable and is especially sought after in heavily noise-polluted and hot-humid climates cities, such as Southeast Asian cities. However, a solution to provide such a window is non-trivial because the design principles guiding acoustics and ventilation are diametrically opposed. While louvre windows have traditionally been used in communal, healthcare, and some educational setting to provide a balance between acoustics and ventilation benefits, it is still sorely lacking to provide sufficient insertion loss without sacrificing ventilation entirely. A new plenum window design has recently garnered research and market interest to tackle the dichotomous problem. Additionally, the application of active noise control (ANC) in windows is gaining popularity and offers potential solutions to improve noise control without compromising ventilation. However, it remains unclear how different traditional and modern window designs compare in terms of their acoustic performance, especially when exposed to non-stationary noise sources such as urban traffic, a major noise pollutant. Thus, the present study seeks to provide a generalization of insertion loss provided by different window designs exposed to moving sources including a tangent study on ANC implementation via a time-domain approach.

Noise and vibration regulations for Uganda - with consideration for people and the environment

As part of a cooperation between the Norwegian Environment Agency and the National Environment Management Authority in Uganda, we have worked on the development of legal noise and vibration regulations for Uganda. In this paper, we address the various noise sources that are relevant for Uganda and its inhabitants. We discuss how these can be regulated bearing in mind that Uganda is an "outdoor society", while Norway is an "indoor society", like the rest of northern Europe. Regulating noise is in many ways a luxury phenomenon, especially in Norway, which has a well implemented system with regulations and guidelines. Solutions that work in Norway can therefore not be implemented in Uganda in the same way. The same with limit values: these cannot just be copied. We discuss the process and present the framework for a system where the emphasis is on regulating activities and their time of day, more than levels - this is easier to understand and enforce. The goal is to complete the regulations before the end of 2024 and hopefully it will lead to a more sustainable society, where e.g. fewer children are awake at night, because the bar in the street is open around the clock.

Comparative analysis of CNN and TNN models in environmental noise source identification

This paper presents a focused examination of environmental noise, an issue of relevance due to its implications for human health and well-being, compliant with ISO 1996-2:2017 standards. Moving beyond the traditional methodologies that primarily rely on level exceedance, our study integrates advanced machine learning techniques to address the challenges in noise source identification. With the advent of IoT Noise Monitoring Terminals, the conventional manual auditory analysis methods have become less feasible. Our research explores the application of convolutional neural networks (CNNs), a standard in environmental noise analysis, and assesses the emerging utility of Transformer Neural Network (TNN) models in this domain. The aim is to conduct an objective comparison of these models, applying them to identical datasets to determine their effectiveness in identifying noise sources. Through this analysis, the study seeks to contribute to the field of environmental acoustics by offering insights into the comparative strengths and limitations of CNN and TNN models.

Sources for railway community noise modeling

For rail traffic, the wheel-rail interaction is one of the most important sources of noise, and is included in different ways in the noise calculation methods being used in Sweden today. However, if the rolling stock exhibit other noise sources it is not clear how they are handled by the different calculation methods. Recent measurements in Sweden of the newly refurbished 'X2' passenger trains indicate that cooling fan exhausts mounted high up on the driving unit radiate noise at levels corresponding to the wheel-rail noise at speeds of 200 km/h. The NMT96 calculation method currently used in Sweden represents the whole train as one line source per octave band, each placed at different heights. The newer Nord 2000 method, applies three sources at low heights for rolling noise and allows additional sources but without defining how to accommodate them. The Cnossos-EU method puts all potential exhaust and fan noise at the higher of two sources, at 4 m above the rail. None of the models define how to apply a source to just the locomotive as sound power is given per meter train or per rolling axis. The impact on noise exposure and mitigation is discussed in this paper.

Attitudes and preferences of the Swiss population towards noise abatement measures: Results from a nationwide panel survey

As part of the Swiss Environmental Panel (SEP) survey, conducted jointly by ETH Zurich and the Swiss Federal Office for the Environment (FOEN), we aimed at obtaining a representative picture of the Swiss people's attitudes regarding noise and noise sources as well as their opinions and preferences about the currently implemented institutional noise protection measures. Knowledge of people's attitudes in this domain is very useful for policy makers, the public administration and the wider public. Survey topics included: degree of satisfaction with the current state of noise abatement, annoyance by emerging new sources, the attitudes vis à vis speed reductions and other noise abatement measures at source, the reasons one is in favor or against these measures, the sanctioning of excessively loud car enthusiasts ("posers" as they are also called), or the installment of "noise radars" to catch and punish noise offenders. Stratified analyses consider political and environmental orientation, age group, degree of urbanization, and socioeconomic status. Data gathering was carried out between May and August 2023 and involved more than 7000 respondents across whole Switzerland.

Effect of Airfoil thickness on low-frequency gust-airfoil interaction noise

Interaction between turbulence and an airfoil is a significant aerodynamic noise source for many engineering applications when turbulence in the wake of upstream blades interacts with the leading edge of downstream blades. Modeling the oncoming turbulence as harmonic gusts is a common approach to studying the noise generated by turbulence-airfoil interaction. The airfoil can be considered a compact noise source, resulting in a dipole-like sound directivity pattern when the acoustic wavelength of gust-airfoil interaction is much larger than the airfoil chord length. However, the interaction becomes more complex when the acoustic wavelength is comparable to or smaller than the airfoil chord, as the airfoil cannot be treated as a compact source anymore and multiple lobes appear in the radiated sound directivity. This paper studies airfoil thickness effects using a computational aeroacoustics approach based on the spectral/hp element method for low-reduced frequency gusts. It is found that the sound pressure decreases with the increase of thickness for low reduced frequency gusts. To reveal its mechanism, a semi-analytical method and the convective FW-H equation are used for low reduced frequency to analyze the radiated noise. The interaction between sound sources on the airfoil surface is crucial for the thickness effect.

Small-scale noise mapping for arbitrary regions using open source noise prediction module "NoiseModelling" and global databases

Extensive noise mapping has been crucial in shaping noise mitigation policies; however, assessing noise exposure in different scenarios remains challenging due to static maps that only represent pre-calculated sound levels. To fill this gap, this study introduces a novel noise mapping framework tailored to calculate sound levels in specific environments within small, arbitrary regions. Using the open-source noise prediction tool NoiseModelling and global databases of road networks, buildings, terrain, and population distribution on QGIS, this framework seamlessly integrates noise mapping procedures, including comprehensive data collection, receiver placement, sound level calculation, and visualization. The user-friendly graphical interfaces enable quick and easy generation of noise maps. The approach offers flexibility through customizable geometry and parameter settings to account for variations in noise sources and propagation characteristics, thereby providing stakeholders with valuable insights for policy formulation, environmental impact assessment, and community engagement. This methodology not only improves the accessibility and relevance of noise mapping but also empowers decision makers to implement tailored noise mitigation strategies that promote healthier and more livable environments.

Study of speech intelligibility in anechoic and reverberant environments using Slovak language

Binaural aspects play a significant role in speech intelligibility, with listeners demonstrating better performance in scenarios where the signal and noise sources are spatially separated, leveraging interaural time and level differences for improved sound segregation and localization. Thus, the question is: How do binaural aspects influence speech intelligibility in different spatial configurations of signal and noise? In this paper, speech intelligibility is examined in an anechoic and reverberant environment, specifically focusing on three configurations of signal and noise: (1) signal and noise both coming from the front at a distance of 1-meter, (2) signal from the front and noise from the right side (90 degrees) at a 1-meter distance, and (3) signal from the front and noise from the back (180 degrees) at a 1-meter distance. The study employs two different noises-speech-weighted noise and multi-talker noise-during listening tests conducted in the Slovak language. Furthermore, the study compares the outcomes with a similar experiment conducted a few years ago in the Dutch language, providing valuable insights into language-specific variations in speech perception under different acoustic environments.

Road traffic noise assessment method for Hong Kong and associated GIS-based assessment tools

Hong Kong, known for its compact and complex urban environment, has long faced unique challenges in modeling road traffic noise for planning and assessment purposes. The Environmental Protection Department (EPD) of the Hong Kong Special Administrative Region Government (HKSARG) identified and established an enhanced prediction methodology called Road Traffic Noise Assessment Method - Hong Kong (RONOSS-HK). RONOSS-HK aims to provide better treatment on source geometry, source terms, noise propagation, considerations for new-energy vehicles and special noise reduction of the Innovative Noise Mitigation Designs (INMD) to cater for the complicated spatial noise situations in Hong Kong. To facilitate the implementation of RONOSS-HK, the EPD has also developed and introduced a GIS-based assessment tool which allows users to utilize GIS data readily available in HKSARG databases and other spatial information in the public domain for accurate road traffic noise prediction using RONOSS-HK methodology. Additionally, the EPD is in the process of further developing a web-based 3D software to serve as an alternative comprehensive assessment tool for applying RONOSS-HK in noise assessment. This paper introduces RONOSS-HK prediction methodology and the latest development of its associated GIS-based assessment tools.

Comparing outdoor sound propagation simulations based on geometrical and numerical methods

Conventional simulations of outdoor noise propagation often rely on geometrical acoustic methods such as ray tracing or mirror sources. Especially for low frequencies, these methods deliver physically implausible results due to their inherent approach not resolving the properties of the acoustic field. In this contribution, the results of a conventional noise propagation simulation software based on geometrical acoustics are compared to numerical results originating from solving the Helmholtz equation with the Finite Element Method (FEM). A 2.6 km long cross-section through an alpine valley with a railway line is considered as an exemple. In comparison with the FEM results, the shortcomings of geometrical acoustic methods are demonstrated, which underline the need for powerful and computationally efficient numerical approaches for outdoor noise propagation.