Noise Level Research Articles

Measures to abate railway noise

An important environmental issue in densely populated areas, such as Germany or France, is the problem of noise. Traffic noise from cars, railway vehicles and airports located in close proximity to the city is not only annoying for residents; it also leads to serious health issues and has an enormous negative economic impact. Unlike road traffic noise, which occurs virtually everywhere, rail traffic noise is much more localized to individual transport corridors. However, depending on the type of train and the volume of trains, high levels of noise can be generated, especially along freight corridors on which most of the rail traffic is at night. One example is the Middle Rhine Valley, which is part of the European freight corridor between Rotterdam and Genoa. In many places along this corridor, the noise levels are essentially higher than those considered desirable to maintain good health. The noise caused by rail traffic is therefore the ecological Achilles heel of the railway. However, there are measures for the reduction of noise emitted by rail traffic. In a recent research project, the German Environment Agency evaluated technical, operational and legal measures to abate the railway noise.

Sensitivity analysis of landing and takeoff noise for conceptual low-boom supersonic aircraft using variable noise reduction system

This paper presents the results of an analysis of the sensitivity of the use of a variable noise reduction system (VNRS), considered in the new landing and takeoff (LTO) noise standard for supersonic aircraft, using a Japan Aerospace Exploration Agency (JAXA)-designed 66-ton twin-engine conceptual low-boom supersonic airliner as an example. The analysis was conducted using a tool developed by JAXA and examined the sensitivity of low-speed aerodynamic performance, the sensitivity of takeoff reference speed, the sensitivity of thrust control and flap control duration time ranges, and the sensitivity of noise level to takeoff profile uncertainty. The analyses showed that improving low-speed aerodynamic performance and increasing the takeoff reference speed significantly impact noise levels and the use of VNRS could reduce noise by 2.1 EPNLdB while maintaining the performance of the aircraft. Because the effective noise reduction method by changing the takeoff procedure considered differs for each noise measurement point, it is important to design a takeoff procedure that incorporates an appropriate VNRS. Uncertainty of the takeoff profile was also investigated using Monte Carlo simulations, and it was shown that noise reduction by VNRS is effective even with the assumed uncertainty in the takeoff profile.

Nationwide noise mapping across Sweden's green landscape

This research project presents a mapping of noise levels in green areas across all of Sweden, with a particular emphasis on nature reserves, national parks, and other recreational spaces. Utilising the Nord2000 noise prediction method, our study incorporates the following noise sources: road traffic, railway traffic, wind turbines, and airports. Our analysis includes longer propagation distances than typical noise maps (up to 8 km) to account for distant sources, given the importance of low noise levels in pristine natural environments. Weather conditions play a crucial role in long-range sound propagation; therefore, we have integrated ten years of weather statistics (2013-2022) from the ERA5 climate dataset into our assessment. This mapping effort represents one of the first nationwide noise mapping initiatives with a specific focus on low-exposure natural areas. Our findings not only provide valuable insights for policymakers and stakeholders in managing and preserving the acoustic quality of Sweden's green spaces but also offer a foundation for analysing the potential impact of noise pollution on wildlife and biodiversity within these ecologically sensitive areas. The resulting noise map and relevant weather statistics are publicly released and downloadable. Participants from industry, government, and academia cooperated in this environmental monitoring project.

Acoustic pattern of a full scale simplified ship

Underwater radiated noise from ship propellers is one of the major contributors to the increase in overall noise levels in marine environments. The development of numerical tools for the computation of noise propagation is of paramount importance for the assessment of the noise impact on the environment. Hybrid approaches, based on the decoupling of the computation of the fluid flow and the successive evolution of the noise using an acoustic analogy, are typically conducted in open-water conditions, which do not correspond to a realistic environment. The Full Acoustic Analogy, which couples a propagation model based on the solution of the acoustic wave equation to the hybrid approach, enables the propagation of the noise generated by a marine propeller in a confined heterogeneous domain. The near-field scattering characteristics of a simplified hull positioned in front of a ship's propeller are analyzed in shallow and deep water, in the presence of the free surface, and compared to the open water case. The analysis determines the directivity of the propeller noise and how this may affect how the noise propagates in the marine environment.

Sound absorbing chandeliers for multitalker noise control in large halls

During social gatherings in large halls, multiple conversations taking place simultaneously can lead to very high noise levels. Increasing the amount of sound absorption in the hall can be very effective in this context: due to the Lombard effect, the noise level drops with 6 dB when doubling the equivalent absorption area, while only a 3 dB drop occurs for sources of constant sound power. However, the possibilities for the absorptive treatment of existing venues can be highly limited, especially when dealing with architectural heritage. Therefore, in the present study, sound absorbing chandeliers, consisting of dense arrangements of absorbing objects, have been designed, developed, tested, and applied in a hard-walled historic hall that hosts social gatherings of more than 800 people. Experiments in the hall during busy events have confirmed the effectiveness of the chandeliers, yet it was also found that, since the ceiling has become the main absorptive surface, they loose efficiency due to the resulting sound field directionality. Furthermore, the individual vocal effort was observed to stay constant when the background nose level was decreasing. Both effects have been thoroughly studied and analyzed, and a prediction methodology to account for these effects has been proposed.

ADAPTIVE METHOD OF FORMING COMPLEX SIGNALS ENSEMBLES BASED ON MULTI-LEVEL RECURRENT TIME-FREQUENCY SEGMENT MODELING

The article investigates the implementation of an adaptive method for forming ensembles of complex signals based on multilevel recurrent time-frequency segmentation. It addresses the key challenges faced by cognitive wireless networks operating in dynamic radio frequency environments with high levels of interference, necessitating rapid adaptation to changes in the spectral characteristics of signals. The study substantiates the need for adaptive filters and specific transformations to enhance signal processing quality, particularly in environments with high variability in frequency characteristics and significant noise interference. The proposed method of multilevel recurrent time-frequency segmentation allows for the modification of time segment durations and the use of segments of varying lengths, providing flexibility in signal processing and adaptation to current conditions. This adaptability enables optimal signal processing for each individual case, taking into account short-term impulses, long-term fluctuations, and various types of noise and distortions. This approach effectively separates frequency components and reduces interference between them, which is crucial for maintaining high signal quality and communication stability in cognitive networks. It has been proven that the use of adaptive filters such as LMS (Least Mean Squares) and RLS (Recursive Least Squares), as well as fast Fourier Transform (STFT), wavelet, and Hilbert transforms at different stages of multilevel time-frequency segmentation, significantly enhances signal interference resistance and energy efficiency. Comparative analysis of signal metrics before and after filtering and transformation shows an increase in signal quality by 14,3–24,5% and a reduction in noise levels by 21,7–29,6%. The wavelet transform, in particular, proved to be highly effective, allowing for precise extraction of useful frequency components from the noise background and improving signal parameters through dynamic adjustment to specific radio environment conditions. Experimental results confirm the effectiveness of the proposed method, demonstrating its ability to ensure consistently high-quality processing of complex signal ensembles even in dynamic cognitive radio environments.

Indiscernible noise determination of a military system equipped with an internal combustion engine

The main objective of this paper is to explore the non-detectability criteria of military systems and to determine the indiscernible noise of military systems equipped with internal combustion engines. Non-detectability is one of the critical requirements evaluated for military defense systems and it is defined strictly in MIL-STD-1474E standard. Furthermore, this standard specifies the limits of sound pressure levels conservatively for 1/3 octave bands. Though, the standard does not define indiscernible or inaudible noise levels for events in the presence of background noise. It is also not explicitly well-defined in the existing literature. This study presents a comparison of non-detectability distance defined in MIL-STD-1474E standard and indiscernible noise of a military system extracted from the measured octave band sound levels, which are processed based on sound propagation theory. In this study, several parameters such as atmospheric absorption, geometric spreading, ground effect, terrain type, obstacle existence are included to determine the indiscernible noise level of the military system of interest. The results are compared with the non-detectability distance limits given in the MIL-STD-1474E standard, and it is observed that the proposed method of indiscernible noise, which is defined as extracted sound level should be lower than the background noise, is well-correlated.

Investigation on supersonic jet noise reduction by water injection: Effects of water injection parameters

In order to protect the payload and the rocket structure from severe vibrations, water injection is commonly used on launch pads to reduce the high noise level radiated by supersonic plumes at lift-off. Even if this technique is widely used, the mechanisms behind sound reduction remain unclear. Sound reduction occurs due to multiple phenomena, each of them having different effects on the jet noise. Experiments based on acoustic measurements have been carried out on a hot supersonic jet on MARTEL facility (Mach number of 3 and a total temperature of 1700 K) to deeper identify the effect of evaporation and water injection parameters. Water flow rate, water injection speed and injection distance to the nozzle have been tested independently to identify the most important water injection parameters. It appears that water flow rate is the most important parameter to decrease noise level and that injecting water at high speed results in noise increase in the downstream direction. Results also highlight the importance of having liquid droplets at the end of the potential core to reduce noise.

NVH multiobjective and robust optimization of electric motor design, including power losses

As part of electric motor design, compromises between NVH considerations, electrotechnical design and performance targets must be made. Electromagnetic excitation within the airgap results in structure-borne and airborne noise transmission to the vehicle. High-frequency tones are characteristic of this noise. Efficient computation methods exist to estimate these vibration and noise levels. From the early design stage, NVH performance can be diagnosed and optimized. The focus on NVH can no longer be separated from efficiency optimization. Simulation workflows and optimization loops, developed for NVH-related targets, are updated to consider copper and iron losses. The modification of the geometrical design must be addressed to reduce both dynamic excitation and energy loss, or at least offer compromises. Electric motor design optimization requires the handling of multiple objectives and constraints from multiple physics. In addition, design robustness must be ensured as part of the industrial process: manufacturing tolerances have to be considered to define a robust optimized design.

The effect of combined exposure to noise and vibrations from rail traffic on sleep: results from the follow-up study "Living in the vicinity of the railway"

As a result of policy aims to improve accessibility and achieve climate targets, an increase in rail traffic is foreseen for a while. It is therefore expected that in the future more problems will arise due to the vibrations and noise that trains produce. It is demonstrated that most problems are caused by freight trains, predominantly tracking during the night, hence affecting sleep. Research has shown that both noise and vibrations from rail traffic can affect sleep; evidence on the impact of combined exposures is scarce. To investigate the effect of combined exposure to noise and vibrations from rail traffic on self-reported sleep disturbance, we used data from a survey aimed to investigate people's reactions on railway vibrations. In 2021, 17,189 people of 16 years and older, living within 300 meters of a railway track in The Netherlands were invited to fill in a questionnaire. Exposure to vibration and noise levels from rail traffic during the night were modelled and linked to the addresses of the 5,611 (33%) participants. We used logistic regression models to test the associations between rail traffic vibration or noise exposure and sleep disturbance for different noise and vibration exposure groups. This paper presents preliminary results.

Interference of mid-level sound statistics underlie human speech recognition sensitivity in natural noise.

Recognizing speech in noise, such as in a busy restaurant, is an essential cognitive skill where the task difficulty varies across environments and noise levels. Although there is growing evidence that the auditory system relies on statistical representations for perceiving 1-5 and coding4,6-9 natural sounds, it's less clear how statistical cues and neural representations contribute to segregating speech in natural auditory scenes. We demonstrate that human listeners rely on mid-level statistics to segregate and recognize speech in environmental noise. Using natural backgrounds and variants with perturbed spectro-temporal statistics, we show that speech recognition accuracy at a fixed noise level varies extensively across natural backgrounds (0% to 100%). Furthermore, for each background the unique interference created by summary statistics can mask or unmask speech, thus hindering or improving speech recognition. To identify the neural coding strategy and statistical cues that influence accuracy, we developed generalized perceptual regression, a framework that links summary statistics from a neural model to word recognition accuracy. Whereas a peripheral cochlear model accounts for only 60% of perceptual variance, summary statistics from a mid-level auditory midbrain model accurately predicts single trial sensory judgments, accounting for more than 90% of the perceptual variance. Furthermore, perceptual weights from the regression framework identify which statistics and tuned neural filters are influential and how they impact recognition. Thus, perception of speech in natural backgrounds relies on a mid-level auditory representation involving interference of multiple summary statistics that impact recognition beneficially or detrimentally across natural background sounds.

Operating room soundscape design intervention study

Noise levels in a typical Operating Room are often well beyond the recommended 45dB for a typical OR environment. Due to stringent cleanability requirements in hospitals, there are limited finishes that can be used in these rooms. Researchers from Gresham Smith and Siebein Acoustic are currently engaged in a research project to investigate how the design of the operating room environment can be acoustically optimized for staff well-being and better patient outcomes. . The study focuses on the environmental variables that can be controlled including the effects of diffusing panels, angling of the walls, and the use of special cleanable acoustic finishes on the ceiling in 3 prototypically sized Operating Rooms using 3-dimensional acoustic models. Acoustic metrics including Reverberation Time, Speech Transmission Index and clarity were compared for 11 scenarios. Results from the acoustical modeling showed that, comparing 11 different scenarios, rooms treated with absorption performed "best" on multiple metrics (Reverberation Time, Clarity, Speech Transmission Index/Intelligibility). Future research will be implemented within existing operating rooms of our hospital partner for in situ validation. Acoustical measurements will again be taken and evaluated against the initial findings and the perceptions of the users of the spaces.

A study on the difference in noise reduction between rear and side microphone on CPX measurement method through sound absorption frequency analysis

The road noise evaluation method in Korea is based on the 'noise vibration process test standard' by the Ministry of Environment. In this evaluation method, the noise felt at the sound-receiving point is measured as LAeq. Recently, in order to clarify the noise measurement standards for low-noise pavements, an international standard (ISO11819-2, CPX method) was first introduced in the Porous Pavement Guidelines of the Ministry of Land, Infrastructure and Transport. According to ISO, CPX measurement method adopts side microphones as mandatory, and the rear microphone as optional. Due to the difference in location noise level is different, causing confusion in the road noise evaluation method. Researchers have published several studies in the past that the rear microphone is highly correlated with the equivalent noise level method based on the Korean standard. As a follow-up study to the above results, this study examines the characteristics and causes of the frequency spectrum of the rear and side microphones in the case of dense asphalt pavement and porous asphalt pavement and derives the results through frequency analysis of the sound absorption coefficient test to determine and to contribute improving reliability and institutional rationalization of the CPX measurement method.

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.

Relation between occupation density and ambient noise in open plan offices: a study based on field measurements

Although progress has been made over the last decade on the issue of well-being in open-plan offices, recent surveys show that employees are still dissatisfied with their working environment, particularly the noise environment, remains. However, standards exist to help ensure that open-plan offices are designed to provide the best possible working environment. But, because of the scope of these standards, their recommendations can be contradictory. For example, the French ergonomics standard NF X35-102 makes recommendations on the sizing of workstations, likely to lead to office occupancy densities that are incompatible with the ambient noise level objectives defined in the ISO 22955 standard. To resolve these contradictions, a field measurement protocol was implemented. It consists in (1) a real-time count of the number of people in the office, (2) a measurement of ambient noise, (3) a questionnaire assessing employees' perception of their physical working environment. The data collected in several French companies will make it possible to establish relationships between the ambient noise level, the occupancy density and the perception of noise levels. This paper presents an occupancy sensor developed for this study and measurements of ambient noise level and occupancy ratio during a working day in an open-plan office.

Experimental assessment of isolation performance of a building above metro lines: a case study with dual isolation levels

This paper presents an assessment of the acoustic performance of a five-story residential building constructed directly above a metro line in Prague. The building has been isolated at two levels: first, on top of the distribution beams above the metro tunnel and secondly, at the ground floor. The assessment of the building's performance has been conducted by a direct measurement of ground borne noise radiated inside the rooms and evaluating the vibration transmission loss through the isolation system. The transmission loss assessment was carried out using two different test setups. Firstly, during train pass-byes, ground borne vibrations were simultaneously measured at various locations above and below the vibration cut. Secondly, at the same measurement points, the vibration levels were measured using hammer impacts. Finally, the transmissibility obtained from both test setups was compared and discussed. Additionally, ground borne noise levels were measured inside rooms on different floors above the vibration cut. To identify noise events exclusively associated with train pass-byes, data obtained from synchronized vibration measurements at the center of a room inside an apartment were used. Finally, the measured noise levels were compared with the limit values of noise exposure recommended by the Czech standards.

The effect of aircraft noise on noise annoyance in DEBATS and NORAH pooled analysis: Role of non-acoustic factors

We investigated the dose-response relationship between aircraft noise levels and noise annoyance in the French DEBATS study including 1244 participants in 2013 and a sub-study of the German NORAH study including 1039 participants in 2014. In both studies, annoyance due to aircraft noise was assessed using the ICBEN 5-points question. High annoyance was defined according to ISO/TS-15666 (HAV). Outdoor aircraft noise levels were modelled for the participants' home addresses. The moderation roles of noise sensitivity, gender and age were investigated. About 18% of the participants in the DEBATS study reported to be highly annoyed vs 54% in the NORAH study. The mean noise levels (Lden) were similar (54 dBA in DEBATS and 52 dBA in NORAH). In the pooled analysis, high noise annoyance was associated not only with aircraft noise levels, but also with non-acoustical factors such as noise sensitivity, age and trust in authorities. Noise sensitivity moderates the effect of aircraft noise levels on aircraft noise annoyance (p-value of interaction = 0.02), while age and gender do not.

A numerical analysis of isolated propeller noise using a lattice Boltzmann method approach

Current environmental needs to achieve carbon neutral commercial aviation by 2050 require the development of new technologies and aircraft configurations. Among the different technological developments proposed, the use of open fan or Ultra-High Bypass Ratio configurations is of interest due to their higher propulsive efficiency and performance. To support the development of such technologies, accurate and efficient tools early in the design stages are needed to predict aerodynamic performances and noise levels. One such tool is the lattice Boltzmann method, which can perform high-fidelity aeroacoustic simulations of flows around propellers and engines. The lattice Boltzmann approach can be advantageous over other numerical methods due to its easy integration with complex geometries, its low numerical dissipation properties, and its high level of computational efficiency. This paper presents the aerodynamic and aeroacoustic numerical study of an isolated propeller using the commercial lattice Boltzmann solver ProLB. Large Eddy Simulations were carried out using a compressible hybrid thermal version of the solver. An aeroacoustic analysis using a Ffowcs-Williams and Hawkings acoustic analogy for far-field noise was carried out. The objective is to assess the capabilities of the solver to predict acoustic emissions of an isolated propeller towards the future study of an installed case.

Modelling of passengers behaviour under the influence of noise in public transport buses: a structural equation approach

This study aims to investigate the impact of noise pollution levels on passengers during travel. Specifically, the aim was to explore the interconnections between noise-induced annoyance, sensitivity to noise, sleep disturbances, and physical health problems using a structural equation modelling (SEM) approach. 14 routes were selected for detailed analysis across different time periods. The noise levels were observed, and the impact of these levels on passengers was assessed through a questionnaire survey to know their perception towards noise and its impacts. A total of 252 responses from passengers were collected through the personal interview. Findings reveal that noise pollution levels exceeded 70 dBA on most of the routes. A significance test (t-test) conducted on 15-minute frequency intervals showed no significant difference in noise pollution levels during morning, evening, and afternoon periods. Subjective analysis indicates 31% of passenger were found to be highly annoyed due to noise within public buses. Additionally, 32% and 9% of passengers reported moderate and minimal annoyance, respectively, attributed to traffic and engine noise inside buses. Structural equation approach showed that sensitivity to noise affects the annoyance level most with coefficient 0.76, followed by physical health factors and sleep disturbance with coefficient 0.48 and 0.44 respectively.

Road Traffic Noise Levels Estimations by means of Fully Dynamic and Microscopic Approach Compared to CNOSSOS-EU Model

In the last decades, research has been dedicated to refining models for assessing traffic noise levels, supporting national authorities in addressing associated problems. Progress has shifted from basic statistical models to dynamic ones, typically composed of a Noise Emission Model (NEM) for estimating source sound power levels and a sound propagation model for assessing equivalent noise levels at specific receiver points. These models commonly integrate the average speed of traffic flow as an input variable, placing them in the macroscopic or mesoscopic realm. The CNOSSOS-EU model (reference in Europe) exemplifies this macroscopic approach. However, due to the modular structure of road traffic noise models, a NEM can be coupled with different sound propagation models, facilitating the transition from macroscopic to microscopic assessments. This paper demonstrates the coupling of a NEM with two distinct simplified sound propagation models: CNOSSOS-EU and the sum of Sound Exposure Levels (SEL) models. The latter approach showcases the potential of using individual on-road vehicle speeds as inputs, enabling microscopic noise assessments. Vehicle speed data is extracted from video records, while the goodness of the proposed approaches is tested by comparing the models' estimations with ground truth values recorded on a National Road in Portugal.