Major Noise Sources Research Articles

The influence of urban tree characteristics on environmental noise in Montreal, Canada

BACKGROUND AND AIM: Vegetation can reduce environmental noise, but limited information exists regarding how specific characteristics of trees of the urban forest influence environmental noise. We investigated the physical characteristics of urban trees that influence environmental noise measurements in Montreal, Canada. METHODS: We used Light Detection and Ranging (LiDAR) point cloud data from 2015 to extract the characteristics of all trees across the island of Montreal. Needle and broadleaf trees were distinguished with a Random Forest algorithm. Based on individual tree characteristics, we computed the total area of the tree crown footprint, the mean tree crown centroid height, the mean volume of tree crowns, and the percentage of broadleaf trees within various buffers (250 to 1000m) around 87 noise measurement sites across the city. Noise measurements were taken over a two-week period in the spring of 2010. Random Forest regression models were used to estimate the variation in noise around measurement sites related to tree characteristics, the Normalized Difference Vegetation index (NDVI), and distances of the measurement sites to major noise sources (highways, railways, and roads). RESULTS:The 24-hour equivalent noise levels averaged across the 87 monitoring sites were 57.5 + 5.1 dBA. The mean crown centroid tree height (5.2 + 0.4m) and the total area of crown footprint (130.7k + 63.4m2) within 500m of each site location were the strongest predictors of measured noise levels. The percentage increased mean squared errors indicated that in 500m buffers, the total area of the crown footprint (29.2%) and the mean crown centroid height (12.6%) were associated with a stronger noise decrease than NDVI (3.2%); similar patterns were observed with other buffers. CONCLUSIONS:Our findings suggest that tree crown footprint and centroid height, and not just the overall amount of vegetation, may play a vital role in reducing urban noise levels. KEYWORDS: Built environment, Green space, Noise

Tree characteristics and environmental noise in complex urban settings – A case study from Montreal, Canada

Field studies have shown that dense tree canopies and regular tree arrangements reduce noise from a point source. In urban areas, noise sources are multiple and tree arrangements are rarely dense. There is a lack of data on the association between the urban tree canopy characteristics and noise in complex urban settings. Our aim was to investigate the spatial variation of urban tree canopy characteristics, indices of vegetation abundance, and environmental noise levels. Using Light Detection and Ranging point cloud data for 2015, we extracted the characteristics of 1,272,069 public and private trees across the island of Montreal, Canada. We distinguished needle-leaf from broadleaf trees, and calculated the percentage of broadleaf trees, the total area of the crown footprint, the mean crown centroid height, and the mean volume of crowns of trees that were located within 100m, 250m, 500m, and 1000m buffers around 87 in situ noise measurement sites. A random forest model incorporating tree characteristics, the normalized difference vegetation index (NDVI) values, and the distances to major urban noise sources (highways, railways and roads) was employed to estimate variation in noise among measurement locations. We found decreasing trends in noise levels with increases in total area of the crown footprint and mean crown centroid height. The percentages of increased mean squared error of the regression models indicated that in 500m buffers the total area of the crown footprint (29.2%) and the mean crown centroid height (12.6%) had a stronger influence than NDVI (3.2%) in modeling noise levels; similar patterns of influence were observed using other buffers. Our findings suggest that municipal initiatives designed to reduce urban noise should account for tree features, and not just the number of trees or the overall amount of vegetation.

Newborn Incubators Do Not Protect from High Noise Levels in the Neonatal Intensive Care Unit and Are Relevant Noise Sources by Themselves.

Background: While meaningful sound exposure has been shown to be important for newborn development, an excess of noise can delay the proper development of the auditory cortex. Aim: The aim of this study was to assess the acoustic environment of a preterm baby in an incubator on a newborn intensive care unit (NICU). Methods: An empty but running incubator (Giraffe Omnibed, GE Healthcare) was used to evaluate the incubator frequency response with 60 measurements. In addition, a full day and night period outside and inside the incubator at the NICU of the University Hospital Zurich was acoustically analyzed. Results: The fan construction inside the incubator generates noise in the frequency range of 1.3–1.5 kHz with a weighted sound pressure level (SPL) of 40.5 dB(A). The construction of the incubator narrows the transmitted frequency spectrum of sound entering the incubator to lower frequencies, but it does not attenuate transient noises such as alarms or opening and closing of cabinet doors substantially. Alarms, as generated by the monitors, the incubator, and additional devices, still pass to the newborn. Conclusions: The incubator does protect only insufficiently from noise coming from the NICUThe transmitted frequency spectrum is changed, limiting the impact of NICU noise on the neonate, but also limiting the neonate’s perception of voices. The incubator, in particular its fan, as well as alarms from patient monitors are major sources of noise. Further optimizations with regard to the sound exposure in the NICU, as well as studies on the role of the incubator as a source and modulator, are needed to meet the preterm infants’ multi-sensory needs.

Fish sounds and boat noise are prominent soundscape contributors in an urban European estuary

Passive acoustic monitoring is a valuable tool for non-intrusive monitoring of marine environments, also allowing the assessment of underwater noise that can negatively affect marine organisms. Here we provide for the first time, an assessment of noise levels and temporal soundscape patterns for a European estuary. We used several eco-acoustics methodologies to characterize the data collected over six weeks within May 2016 - July 2017 from Tagus estuary. Biophony was the major contributor dominated by fish vocalizations and the main driver for seasonal patterns. Maritime traffic was the major source of anthropogenic noise, with daily patterns monitored using 1584 Hz third-octave band level. This indicator avoided biophony and geophony, unlike other indicators proposed for the EU Marine Strategy Framework Directive. Furthermore, the frequency overlap between anthropophony and biophony demands precautionary actions and calls for further research. This study provides an assessment that will be useful for future monitoring and management strategies.

Experimental assessment of the noise characteristics of propellers for commercial drones

Multi-copters or drones are engaged in a wide range of industrial applications for their flexibility, safety and low-cost. The noise emission is becoming an issue with the expanding applications, among which the propellers that drive the drones are the major sources of noise. In this work, the noise characteristics of small-scale propellers is experimentally investigated using the advanced rotor aerodynamics and aeroacoustics test platform in an anechoic chamber at the Hong Kong University of Science and Technology (HKUST). The study will focus on the representative off-the-shelf propellers. The rotor noise will be measured by a linear array with 20 microphones, and the aerodynamic forces will be acquired by using the high-accuracy load cells. The dependence of both the tonal and broadband noise radiation with the thrust and rotation speed at various conditions will be tested. The study will enhance our understanding of the noise features of the multi-rotor powered drones, and will provide us with a better understanding of the status of the drone noise impact on the environment.

Control of low frequency noise from an environmental test facility

Environmental test chambers are used in the automotive industry to verify the resilience of vehicles. In just a few hours it is possible to take a car from mid-winter in the artic, via a high mountain range, to mid-summer in a desert. Powerful ventilation systems are used to change the temperature, pressure and humidity of the air in the chamber, and the variable speed blowers are a major source of low frequency noise, which can cause significant disturbance at neighbouring properties if there are gaps in silencer performance. This paper details a study to assess the attenuation requirements for a system to meet a standard criterion for low frequency far-field noise levels, and to select a reactive silencer system to achieve that specification under all circumstances. The system used standard silencer components where possible, but needed to take account of long pipe runs through the facility, with tailpipe resonances being a particular issue, and was further constrained by space and loading limits for the building. Design layouts were verified using the Actran FE code, taking account of interactions with existing silencers and transfer functions to the far-field, in order to have very high confidence of a successful outcome.

Experimental Observations in Tire Cavity Resonance and Interactions with Periodic Noise Components

Tire cavity resonance is one of the major sources of tire-related in-cabin noise and vibration. It has gained more attention in recent years with the growth of the electric vehicle market. This is due to the absence of masking noise from the internal combustion engine and powertrain. Thus, the mitigation of this issue has become a critical task for tire and vehicle manufacturers. The excited cavity resonant frequency in an unloaded condition is typically between 170 - 220 Hz. However, multiple studies have shown that loading the tire will result in two dominant resonances transmitted into the cavity. Their corresponding mode shapes are typically described in terms of the direction of their characteristic acoustic pressure variation i.e., fore-aft cavity mode and vertical cavity mode. As the tire's rotational speed increases, in-cabin measurements show that the tire cavity resonant frequencies separate from each other. Further, interactions with the periodic component of tire noise at certain speeds are also observed. These periodic components can be attributed to tire non-uniformities and tread pattern related excitation. This interaction is perceived as tonal noise inside the vehicle cabin at discrete speeds. This work presents experimental results summarizing these findings.

Noise prediction for urban air taxi operation

Solutions to escape crowded streets are increasingly taking up new forms of mobility. This also includes air taxis or VTOLs. In addition to passenger traffic, suggestions, such as parcel delivery by drones, are also regularly part of future visions. Air taxis pose additional safety requirements due to the transport of people and they also represent a major potential source of noise. A challenge that urban planners, pollution control officers and decision-makers have to face. Using the concrete example of an urban landing place for air taxis at the main train station in the city of Ingolstadt, possible problems, issues related to noise protection and their legal basis were examined. This presentation is a summary of the projects results. The examinations include the creation of noise mapping in order to simulate the impact to the already existing noise situation. Those were based on current flight noise regulations with necessary alterations regarding VTOLs. Because air taxi noise is expected to be more annoying than regular traffic noise, the possible application of flight noise indexes such as the "Frankfurt flight noise index FFI 2.0" shall be reviewed. Based on the results of the previous examinations, possible noise protection measures shall be developed.

Subjective responses between real impact sound and rubber ball im-pact sound

By the recent COVID-19 situation, people stay more time in their home and abatements on noise between neighbouring units are increasing. Heavy/soft impact sound is one of the major noise sources in high-rise apartment buildings. Standardized heavy/soft impact source is known for having the most similar physical and subjective characteristics with real impact sound such as a child running, jumping and an adult walking. The single number quantity on the rubber ball was standardized. A classification scheme for rubber ball impact sound needs to be standardized. Several studies on subjective responses were conducted on rubber ball impact sound in various situations. In this study, subjective responses on the rubber impact sound and real impact sound were compared. The subjective experiment was conducted in the listening chamber which is furnished similarly to the typical living room of Korean apartment buildings. In the experiment, rubber ball impact sounds recorded in the real apartment building and real impact sound recorded in the mock-up building were presented through a sub-woofer and multi-channel loudspeaker system. Subjective responses were collected with an 11 points SD scale.

A Sample Preparation Pipeline for Microcrystals at the VMXm Beamline.

The mounting of microcrystals (<10 µm) for single crystal cryo-crystallography presents a non-trivial challenge. Improvements in data quality have been seen for microcrystals with the development of beamline optics, beam stability and variable beam size focusing from submicron to microns, such as at the VMXm beamline at Diamond Light Source1. Further improvements in data quality will be gained through improvements in sample environment and sample preparation. Microcrystals inherently generate weaker diffraction, therefore improving the signal-to-noise is key to collecting quality X-ray diffraction data and will predominantly come from reductions in background noise. Major sources of X-ray background noise in a diffraction experiment are from their interaction with the air path before and after the sample, excess crystallization solution surrounding the sample, the presence of crystalline ice and scatter from any other beamline instrumentation or X-ray windows. The VMXm beamline comprises instrumentation and a sample preparation protocol to reduce all these sources of noise. Firstly, an in-vacuum sample environment at VMXm removes the air path between X-ray source and sample. Next, sample preparation protocols for macromolecular crystallography at VMXm utilize a number of processes and tools adapted from cryoTEM. These include copper grids with holey carbon support films, automated blotting and plunge cooling robotics making use of liquid ethane. These tools enable the preparation of hundreds of microcrystals on a single cryoTEM grid with minimal surrounding liquid on a low-noise support. They also minimize the formation of crystalline ice from any remaining liquid surrounding the crystals. We present the process for preparing and assessing the quality of soluble protein microcrystals using visible light and scanning electron microscopy before mounting the samples on the VMXm beamline for X-ray diffraction experiments. We will also provide examples of good quality samples as well as those which require further optimization and strategies to do so.

A Sample Preparation Pipeline for Microcrystals at the VMXm Beamline

The mounting of microcrystals (<10 µm) for single crystal cryo-crystallography presents a non-trivial challenge. Improvements in data quality have been seen for microcrystals with the development of beamline optics, beam stability and variable beam size focusing from submicron to microns, such as at the VMXm beamline at Diamond Light Source1. Further improvements in data quality will be gained through improvements in sample environment and sample preparation. Microcrystals inherently generate weaker diffraction, therefore improving the signal-to-noise is key to collecting quality X-ray diffraction data and will predominantly come from reductions in background noise. Major sources of X-ray background noise in a diffraction experiment are from their interaction with the air path before and after the sample, excess crystallization solution surrounding the sample, the presence of crystalline ice and scatter from any other beamline instrumentation or X-ray windows. The VMXm beamline comprises instrumentation and a sample preparation protocol to reduce all these sources of noise. Firstly, an in-vacuum sample environment at VMXm removes the air path between X-ray source and sample. Next, sample preparation protocols for macromolecular crystallography at VMXm utilize a number of processes and tools adapted from cryoTEM. These include copper grids with holey carbon support films, automated blotting and plunge cooling robotics making use of liquid ethane. These tools enable the preparation of hundreds of microcrystals on a single cryoTEM grid with minimal surrounding liquid on a low-noise support. They also minimize the formation of crystalline ice from any remaining liquid surrounding the crystals. We present the process for preparing and assessing the quality of soluble protein microcrystals using visible light and scanning electron microscopy before mounting the samples on the VMXm beamline for X-ray diffraction experiments. We will also provide examples of good quality samples as well as those which require further optimization and strategies to do so.

Multidimensional Psychological Evaluation of Air Conditioner Sounds and Prediction via Correlation Parameters

Air conditioners are regarded as a major source of noise in built environments. Although noise control technology has reduced the sound produced by air conditioners to a comparatively low level, some people may still feel that certain aspects of the sound quality lead to discomfort. Indeed, both the sound level and the sound quality of an air conditioner can affect user’s acoustic comfort. The aim of this study was to determine the factors that significantly influence the subjective response to the sound of air conditioners. We assessed the A-weighted equivalent continuous sound pressure level (LAeq) and factors extracted from the autocorrelation function (ACF) and interaural cross-correlation (IACF). Subjective loudness, sharpness, and annoyance were evaluated using a paired comparison method. Multiple regression analyses were performed using a linear combination of LAeq, the ACF factors, IACF factors, and assessment of their standard deviations. The multiple regression analyses indicated that LAeq, the delay time of the first maximum peak, the width of the first decay of the ACF, and the magnitude and width of the IACF could predict subjective responses to air conditioner sounds.

On Noise Performance of Dual-Gated Silicon FET Biosensors With Schottky Contacts

We analyzed the low-frequency noise (LFN) of dual-gated field-effect transistor (DG-FET) biosensors with Schottky contacts. We found the flicker noise at the sensing insulator-semiconductor interface to be the major noise source while employing Schottky contacts to have minimal noise contribution with a sufficiently large back-gate bias voltage. The measured noise dependence on transconductance further indicated the presence of a nonuniform energy distribution of interface trap density at the said sensing interface. Based on these findings, we argued that the DG structure is advantageous over its single-gated (SG) counterpart; although they possess the same intrinsic lower limit of detection (LLOD), the former could offer a larger signal gain at the optimum LLOD thanks to sufficient channel carrier supply through back-gating instead of biasing the sensing interface toward band edge with higher trap density.

Localization and characterization of rotating noise sources on axial fans by means of an irregularly shaped microphone array

Aerodynamic noise emitted by low-speed axial fans has been receiving increasing attention in various sectors of high societal impact, such as automotive and HVAC systems. In this framework, turbulence interaction, flow non-uniformities, trailing-edge boundary layer fluctuations and blade-tip leakages are different mechanisms generating aeroacoustic sources on the rotating blades and contributing to the overall emitted sound. An accurate localization of the sound sources on the surface of the blade is instrumental in separating and isolating these contributions and, therefore, in designing novel sound mitigation concepts. The main objective of this paper is to present an inexpensive and efficient way to isolate and quantify the noise generating mechanisms on rotating blades by means of a irregularly shaped microphone array. The technique is based on ROtating Source Identifier (ROSI) and has been implemented and validated at the von Karman Institute for Fluid Dynamics (VKI). Simulated benchmark datasets that refer to rotating point sources emitting white noise have been considered for the validation of the method. The accuracy in the source localization and in the source strength reconstruction has been evaluated for a fixed and a variable angular rate. Moreover, the algorithm implementation has been parallelized with the purpose of reducing its computational time, which represents the main drawback of ROSI. Finally, the developed technique has been applied to measure the noise sources generated by a forward-skewed subsonic axial fan operated at maximum efficiency. In this case, it has been possible to successfully localize and characterize the major noise sources on the blades. Although further investigation will be necessary to gain better insight into the topic, the present work constitutes an important step for a better understanding of the physical phenomena occurring in the noise generation of an axial fan.

Effect of COVID-19 spring lockdown on low-frequency ambient noise levels along the Brittany coast

Shipping noise is a major source of ocean noise in Brest bay, and includes cargo vessels, navy ships, fishing boats and recreational vessels with frequencies overlapping the range of marine animal sound emission. Changes in vessel activity provide unique opportunities to quantify the relationship between traffic levels and soundscape conditions in biologically important habitats. Using an autonomous recorder deployed from March 20 to July 29 2019 inside Sainte-Anne harbor in Brest area we assessed the effect of the 2020 spring COVID-19 lockdown (March 17 to May 11) on ambient noise levels. We measured the mean power spectral density levels in different third-octave bands (including Marine Strategy Framework Directive bands centered on 63 Hz and 125 Hz). The March 20–May 15 (during lockdown) levels were up to 2.6 dB re 1 μPa2/Hz below the May 15–July 28th (after lockdown) levels, corresponding to nearly a halving of acoustic power.

The Effects of Transportation Modes on Noise Pollution in Koya City

Transportation means including all kinds are considered the major and most dangerous source of noise since, on the one hand, they have highest contribution rate in causing noises, and on the other hand, they affect a great number of city inhabitants. Transportation means also has an immediate influence on the peacefulness and living balance amongst people because unnatural sounds creates noise and this causes psychological unrest and ruins the surrounding peace.&nbsp;The study problem is the existence of sound pollution in the selected area of the research which are caused by a number of seen and unseen sources. These sources have to be unveiled pointed to. Solving these problems scientifically and practically is of great benefit for the area. The main aim of this study is to identify the sound pollution sources in the city of Koya and its effects. The study also aims at proposing the best solution possible. Raising the awareness of people to protect the environment, following standard procedures, reducing pollution due to noises, and identifying noise sources. Research plan&nbsp; The aim of the study requires dividing the study into three sections. Section one refers to the theoretical outline of the area under study which includes three themes. The first theme discusses the technical terms and concepts, second theme deals with the major sound pollution sources, and the third one is dedicated to introducing the area of the study. While in section two we have analyzed the time distribution of the noises and their sources in Koya city. This section also have three themes, the first one id devoted to the place of the noise, the second one presents noise time distribution, and the last one light is shed on consequences and solutions of the noises.

A Combined CFD-FEM Approach to Predict Fluid-Borne Vibrations and Noise Radiation of a Rotary Vane Pump

The rising demand for lower noise emissions of car ancillary units due to electrification and higher customer expectations regarding driving comfort results in the need for more silent car components. Hydraulic driven car components in particular are often identified as a major source of noise in the system. Therefore, it is mandatory to investigate the noise sources inside the hydraulic system. In this work, a combined CFD-FEM approach is applied to estimate the flow-induced noise radiation of a mechanically driven transmission pump. To achieve this goal, the mapping procedure to hand over the pressure field from the CFD to the FEM mesh must be valid. For this purpose, the error during the mapping process is evaluated and different parameters, which influence the mapping results, are analyzed. Additionally, the impact of the time step size and the length of the time signal on the frequency resolution of the force signal is investigated to get an appropriate excitation force for the vibroacoustic simulation. Subsequently, a force analysis and a structural FEM simulation are performed to identify which flow phenomenon contributes most to the excitation of the pump housing. Specific locations in the pump with high loads are pointed out. In a final step, the results of the vibroacoustic model are compared to acceleration and sound pressure level measurements of the pump performed in a hemi-anechoic room.

Influence of architectural layouts on noise levels in Danish emergency departments

This study aims to evaluate the effects of architectural layouts of emergency departments on activity patterns/work routines and consequent noise levels. Three Danish hospitals' emergency departments that had different layouts were investigated via on-site noise measurements over three days and observations of noisy activities. The time-averaged noise levels in the three emergency departments turned out to be significantly different, ranging from 50 to 59 dBA. During the observation of noisy activities, the noise levels and occurrences of individual activities were noted and correlated with the long-term measurements. Major noise sources that have high correlations with the three-day noise levels are identified as loud staff communication and noise from alarms/electronic devices. Potential remedies are suggested in connection to the emergency departments’ architectural layouts. Especially unnecessarily loud communication between medical staff and loud and frequent equipment/patient transportation noise need to be improved for more comfortable acoustic environments.

Measuring the phase noise of Raman lasers with an atom-based method.

Phase noise of Raman lasers is a major source of noise for a Raman-type cold atom interferometer, which is traditionally measured using the signal source analyzer. We report here an atom-based method to measure the phase noise performance between two Raman lasers. By analyzing and calibrating the system noise sources, we can characterize the contribution of phase noise from the total deviation of the relative atom population at the middle of the interference fringe. Knowing the transfer function specified by the operation sequence of the interferometer, we can obtain the transfer function and power spectrum density of the phase noise term. By varying the time sequences of the interferometer, we can measure the white phase noise floor and the phase noise performance over a large range of Fourier frequencies from 1 to 100 000Hz with a minor difference of 1 dB compared with results from the traditional method using a signal analyzer, which proves the validity of the atom-based method. Compared with the traditional measurement method, the atom-based method can have higher accuracy and have the ability of self-calibrating.

Analysis and Distribution of Conveyor Belt Noise Sources under Laboratory Conditions

In compliance with ecological policies, activities undertaken by surface mines in relation to environment protection should be comprehensive and must take into account the principle of sustained development. One of the most basic tasks in this area is to reduce the nuisance caused by the noise emitted to the environment. The problem of above-standard noise levels caused by transportation systems operated in mines can be solved only after major noise sources are identified and analyzed in detail. This article first focuses on the literature studies to describe the possible sources of noise generated by a belt conveyor and in its second part it presents exploratory research into noise sources. The research was performed under laboratory conditions with the use of an acoustic camera as a tool for spatially identifying and classifying individual noise sources. The article identifies some phenomena related to the operation of main belt conveyor components and describes their characteristic frequency ranges.