Noise Spectral Characteristics Research Articles

Spectral noise reduction of double-layer porous asphalt: From laboratory to field

The double-layer porous asphalt (DLPA) pavement is a practical way to mitigate traffic noise from the source. However, there hasn't been much research done on the spectral noise characteristics of the car/truck on this type of pavement with different surface conditions yet. The objective of this paper was to reveal these noise characteristics and the behaviors of the DLPA pavement by laboratory tests and field measurements. First, measurements were made of the road performance of different porous asphalt (PA) mixtures and DLPA structures. Then, a vector impedance measurement system was utilized to evaluate the effects of porosity, aggregate size, and thickness on the sound absorption coefficient (SAC) of the DLPA slabs. Third, a sound meter was used to record the noise levels outside/inside the car/truck on the roads with three surface conditions for the DLPA (PA-10+PA-20) and stone matrix asphalt (SMA) test section, which were paved on an elevated urban road. Finally, an analysis was done on the overall and spectral noise characteristics. The results demonstrated good road performance of these PA mixtures and DLPA structures. Relatively fine and coarse aggregates in the upper and lower layers, respectively, enhanced the sound absorption. But an increase in porosity beyond 20 % and a slight variation in thickness did not considerably improve the sound absorption. Compared to SMA pavement, the overall noises levels of the DLPA pavement were 4–8 dBA lower on the “dry” surface and 6 dBA lower on the “wet” surface. The DLPA pavement exhibited a noise reduction at the full frequency band, which attributed to the pore structure and the relatively fine aggregate used. The interior sound energy always concentrated on the low-frequency band. However, the exterior sound energy on the “dry” and “wet” road surfaces tended to the low-frequency and high-frequency bands, respectively. These findings would shed light on the spectral noise characteristics of the DLPA pavement and provide a new knowledge about the behaviors of the lower layer and upper layer in relation to noise reduction and road performance.

Characterization of noise spectra in low-jitter GHz mode-locked fs-laser-inscribed waveguide lasers

We demonstrate low-noise, continuous-wave mode-locking of a diode-pumped Yb:KLuW waveguide laser operating at fundamental repetition rates in the GHz range. Utilizing a femtosecond-laser-inscribed Yb:KLuW channel waveguide laser with a tunable cavity length of a few centimeters, we successfully generate femtosecond pulses near 1030 nm, employing either single-walled carbon nanotubes or semiconductor saturable absorbers. Although timing noise is one of the most critical factors in the implementation of high-repetition-rate laser sources for various applications, investigations into timing noise characteristics in waveguide lasers remain limited. This study fills this gap by presenting timing jitter measurements for GHz mode-locked waveguide lasers with diverse cavity parameters. To quantitatively analyze noise spectral characteristics, including relaxation oscillation processes induced by intensity noise features, we introduce a theoretical modeling approach. The present investigation directly enables the provision of strategies for further suppression of timing jitter and designing high-performance, low-noise mode-locked lasers.

Analysis of signal-to-noise ratio of spatial heterodyne spectroscopy

We have established a novel spatial heterodyne spectroscopy (SHS) signal-to-noise ratio (SNR) model, relating the spectral SNR to the spectral band and resolution, which helps guide the instrument's design and optimization and assess the spectral quality. The experimental and simulation results show that the spectral resolution affects the SNR differently under different noise types and spectral characteristics of the measured targets, which fully validates the novel SHS SNR model. Despite the disadvantage of multiplexing in SHS, we determine the SNR advantage of SHS over the grating spectroscopy (GS) through rigorous theoretical derivations. In 94.34 % of the polychromatic light detections, the average SNR of SHS is 2–31 times higher than that of GS. In emission spectra detections, the SNR gain of SHS relative to GS is up to 1–2 orders of magnitude. In additive noise domination, the SNR gain reaches 1–3 orders of magnitude.

Experimental characterisation of rotor noise in tandem configuration

This paper presents a comprehensive investigation into the noise radiation characteristics of two rotors in a tandem configuration. Through an extensive experimental campaign, the study explores the effect of the separation distance between two rotors on the noise directivity patterns, spectral characteristics and temporal features of the radiated noise under both hovering and edge-wise flight conditions. The directivity patterns of the overall sound pressure level obtained from the polar and side arrays demonstrate a dependence on the separation distance and advance ratio. Spectral characteristics elucidate the influence of separation distance on tonal and broadband energy content. While the high-frequency broadband noise increases for both hovering and edge-wise flight similarly, the low-frequency broadband energy strongly depends on the advance ratio and the rotor separation distance. The results reveal a distinct envelope in the design space, where the radiated broadband noise for tandem configurations can be minimized, offering potential insights for noise reduction strategies. Additionally, the wavelet analysis for tandem configurations reveals that the emitted noise at the first and second blade passing frequency is strongly intermittent with amplitude modulation, which shall be considered for annoyance perception.

Research on the unsteady flow field and aerodynamic noise characteristics in the circular space of ultra-high-speed elevators

Due to the non-streamlined blunt body shape of the elevator car, intense aerodynamic loads and noise are generated in the annular space when the elevator operates at high speed in a narrow hoistway. This article uses large-eddy simulation and Curle acoustic theory to establish a numerical model of the wellbore flow field under different guiding shapes of the elevator car. First, the mechanism of action between the flow guide shape, vortex characteristics, and aerodynamic load was studied, and the influence of operating speed on aerodynamic load under different flow guide shapes was analyzed. Second, the distribution and spectral characteristics of noise in the annular space under different flow guide shapes were studied from the near field and far field scales. Finally, it can be concluded that increasing the guide surface can significantly reduce the pressure difference between the upper and lower parts of the car, weakening the separation of the tail airflow. The number of guide surfaces, installation position, and vertex offset significantly impact drag and lateral force, with the optimal reduction of 34.65% and 57.6%, respectively. The maximum sound source intensity of near-field noise is mainly concentrated at the arc transition in the upper part of the annular space, and the frequency is mainly concentrated in the range of 500–1000 Hz. The sound pressure level is linearly related to the logarithm of the longitudinal distance, and the noise attenuation speed becomes faster with the increase in the number of guiding surfaces.

Comparative analysis of fixed-pitch and variable-pitch control systems for multirotor drones: Acoustic characteristics and rotor phase control

In this study, the aerodynamic and aeroacoustic characteristics of multirotor electric vertical take-off and landing aircraft in hovering and forward flight are compared using two representative control methods: fixed-pitch control and variable-pitch control (i.e., revolution per minute (RPM) control and collective pitch control). To this end, a comprehensive multirotor noise assessment framework is used to predict the aerodynamics and noise of multirotors controlled by RPM and collective pitch. High-resolution time–frequency analysis is used to clarify the differences in noise spectral characteristics. The findings indicate that blade passage frequency characteristics vary significantly depending on the control method. The phase differences between the rotors of variable-pitch control remain constant irrespective of disturbances or attitude control. In other words, the frequencies of the tone noise do not exhibit short-periodic modulation, unlike those of RPM-controlled multirotor. Additionally, the aeroacoustic characteristics of fixed-pitch and variable-pitch controlled multirotor in response to wind velocity fluctuation are investigated by considering the direction of noise radiation and interference effects. The impact of the turbulent kinetic energy of wind on the noise characteristics is examined by quantifying the noise components associated with aerodynamic unsteadiness in flight. Furthermore, the rotor phase control method can be applied to reduce noise in both control methods. The optimization of rotor phases reduces tone noise significantly at the target observer point without causing aerodynamic losses in variable-pitch controlled multirotor. In contrast, the reduction in tone noise remains relatively limited for fixed-pitch controlled multirotor, as the rotor phase differences are not maintained.

The noise spectral characteristics and noise reduction schemes of screw air-source heat pump: A case study

The noise spectral characteristics and noise reduction schemes of screw air-source heat pump: A case study

Spectrogram-based classification on vehicles with modified loud exhausts via convolutional neural networks

Hong Kong is one of the densest cities in the world with busy roads close to residential areas. Excessive noise emitted by vehicles with modified loud exhausts causes further noise annoyance during late night. Existing technologies are inefficient for detecting these undesirable vehicles due to various constrains such as the use of sound level meter requires manual spectrum analysis, and acoustic camera is expensive, bulky for low frequency detection and computationally heavy. In this research, the noise spectral characteristics at the peak sound pressure levels from vehicles observed with and without modified loud exhausts passing-by the measurement points were collected and scientifically analyzed. A spectrogram-based sound recognition prototype with low-cost design was therefore developed in assisting the detection of vehicles with modified loud exhausts. A large amount of audio data was converted into spectrograms by short-time Fourier transform for machine learning and a trained convolutional neural network model based on AlexNet architecture utilized spectrograms as the inputs for classifying whether the pass-by vehicles are with modified loud exhausts. The prototype also deploys YOLO v4 Tiny algorithm for object recognition and is able to distinguish the types of pass-by vehicles i.e. passenger car (which is the target for detection), goods vehicle, and motorcycle for enhancing the usability. The results show that the prototype had reached an overall 96% accuracy in the detection of passenger cars with and without modified loud exhausts.

Tunable performance metrics for acoustic liners

In the development of automated design tools for acoustic liners customized to mitigate specific noise spectral characteristics, it is often beneficial to have a unified quantitative metric to discriminate between candidate designs. Such metrics are especially useful when optimizing the packing of 3D folded cavities into a prescribed liner volume. We devise tunable performance metrics (TPM) that account for absorption parameters such as the peak absorption and the frequency at which it occurs, the bandwidth of appreciable absorption and its lower bound among others. Metrics are tuned by varying the weight functions for these absorption parameters in order to address the specific priorities for the liner’s design. A numerical study is conducted using a procedure based on the Zwikker–Kosten Transmission Line (ZKTL) theory to demonstrate the application of TPMs for the selection of acoustic liner designs for various scenarios. When liners with complex core geometries are used to enhance acoustic performance, TPMs that also include structural parameters related to mass, volume, stiffness or strength could be utilized to provide a more comprehensive means of evaluation.

Риски нарушения здоровья машинистов горных машин от шумо-вибрационного воздействия

Application of heavy-duty mining equipment can change the labor conditions for the employees, the intensity of the existing factors of the working environment and the labor process. Hygienic studies to assess the impact of vibration and acoustic factors on the modified EKG-8 and EKG-10 mechanical shovels and the BELAZ dump trucks showed that the actual noise and vibration levels in the operator cabins are significantly lower than those of the previously produced same types of machines. The probability of workers' complaints of the lower back pain, the risk of developing initial and moderate manifestations of the vibration disease, as well as the early signs of hearing loss and risks of its deterioration among the workers who service upgraded mining machines were calculated using the existing methods based on the obtained spectral characteristics of noise and vibration of the investigated mechanical shovels, dozers, dump trucks. The calculations show that the probability of developing the vibration disease of the 1st degree for operators of mechanical shovels within 10 years of employment decreased from 5.04% to 1.82% at vibration acceleration of 0.19 ms-2, and from 8.68% to 4.41% within 25 years of service. The risk of hearing loss among the personnel operating the upgraded machines is significantly lower and the early signs are observed after 25 or more years of work experience.

Comparative Analysis of Noise Reduction Methods in Car Braking Process on Classification Hump Yards

Technological processes in railway transport create unsafe conditions for employees. One of the harmful factors is noise, which has a negative impact on the physiological condition of people and creates uncomfortable living conditions for people in the adjacent areas. Particular discomfort is caused by high-frequency noise generated by the hump retarders operation on the classification humps. The authors of the present work made an attempt to systematize the characteristics of noise reduction means during detachments braking on classification humps. The study of available in open sources results of scientific researches, proposals of the developers of protection means showed that the existing information in the given direction is insufficient. Acoustic characteristics of the means providing noise reduction sometimes have qualitative description: "more" or "less". Considering that the estimations of comfort for the population living near marshalling station are important spectral characteristics of noise, it is necessary to note that quantitative characteristics do not provide an objective representation about efficiency of the means offered by the developers for noise reduction. Noise measurements on the territory of the housing estate near to a classification hump yard are made, the analysis of the basic ways of noise reduction is executed, the characteristics of the means providing noise reduction are presented, and the directions of the further researches are designated.

A novel geometry image to accurately represent a surface by preserving mesh topology

Geometry images parameterise a mesh with a square domain and store the information in a single chart. A one-to-one correspondence between the 2D plane and the 3D model is convenient for processing 3D models. However, the parameterised vertices are not all located at the intersection of the gridlines the existing geometry images. Thus, errors are unavoidable when a 3D mesh is reconstructed from the chart. In this paper, we propose parameterise surface onto a novel geometry image that preserves the constraint of topological neighbourhood information at integer coordinate points on a 2D grid and ensures that the shape of the reconstructed 3D mesh does not change from supplemented image data. We find a collection of edges that opens the mesh into simply connected surface with a single boundary. The point distribution with approximate blue noise spectral characteristics is computed by capacity-constrained delaunay triangulation without retriangulation. We move the vertices to the constrained mesh intersection, adjust the degenerate triangles on a regular grid, and fill the blank part by performing a local affine transformation between each triangle in the mesh and image. Unlike other geometry images, the proposed method results in no error in the reconstructed surface model when floating-point data are stored in the image. High reconstruction accuracy is achieved when the xyz positions are in a 16-bit data format in each image channel because only rounding errors exist in the topology-preserving geometry images, there are no sampling errors. This method performs one-to-one mapping between the 3D surface mesh and the points in the 2D image, while foldovers do not appear in the 2D triangular mesh, maintaining the topological structure. This also shows the potential of using a 2D image processing algorithm to process 3D models.

NEMO project: developing a N-RSD (Noise Remote Sensing Device) to identify high noise emitters in the road traffic flow

NEMO (Noise and Emissions MOnitoring and Radical mitigation) is a research project aiming at developing an autonomous system to detect noise and air pollutant emissions from individual vehicles within the traffic flow. The objective is to identify high emitters within the normal traffic. For noise, a high emitter is a vehicle that is either in a poor or modified condition (e.g., with an illegal or malfunctioning exhaust) or that is driven in a noisy way (fast acceleration, high engine speed in low gear, etc.). A vehicle that has been type approved, is well maintained, and is driven under normal conditions is never a high-emitter vehicle, even if it is subjectively perceived as annoying. A Noise Remote Sensing Device (N-RSD) is being developed. This device will capture, for each individual vehicle, the driving conditions (vehicle speed, acceleration, engine speed and load) and the single-event noise levels and spectral characteristics. The noise levels will be normalized to comparable driving conditions and fed into a classification model. The classification model will then be able to identify the high emitters vehicles. When finished, the NEMO system will allow cities and road authorities to reduce annoyance and health impacts from noisy and polluting vehicles, for instance by raising awareness among drivers or by restricting access to low emission zones.

Audible noise spectral characteristics of high‐voltage ac bundled conductors at high altitude

At high altitudes, the corona discharge around a conductor surface is severe, and the induced audible noise (AN) is irritating; this is due to the low air density at high altitudes. Therefore, AN has become a crucial limiting factor in the design of ac power lines of 500 kV or higher at high altitudes. An investigation of the spectral characteristics of AN should help provide a greater understanding of corona noise; however, only a few studies have investigated the spectral characteristics of AN in practical bundled conductors at high altitude. Therefore, it is difficult for power utility companies to select suitable conductors. In this study, the AN spectral characteristics of 6 × LGJ400, 6 × LGJ720, and 8 × LGJ500 bundled conductors were investigated using an ultra-high-voltage corona cage (8 × 8 × 35 m) in Xining, Qinghai Province (altitude: 2261 m). The AN equivalent A-weighted level and the 1/3-octave frequency characteristics of these three conductors were obtained, and the influence of the electric field (E-field) on these characteristics was analysed. Subsequently, the relationship between the AN A-weighted level and the 8-kHz level was examined. We found that, with the increase of the E-field, the low-frequency components of AN level did not exhibit an obvious trend, but in the high-frequency band (1.6–20 kHz), a clear positive correlation was observed between the spectrum level and E-field strength. Among these three conductors, the 8 × LGJ500 conductor was the optimal conductor for reducing the AN levels at high altitude. The results obtained in this study can provide a data reference for the construction of high-altitude ac power lines.

EXPERIMENTAL STUDY OF THE NATURE OF ACOUSTIC NOISE SPECTRAL CHARACTERISTICS DISTURBANCE AT A LAB WELLBORE MOCKUP WITH STEEL CASING

Background The possibility of using passive acoustic noise logging in the study of operating wells is considered. Currently, there are several companies on the geophysical services market that offer to implement the method of broadband wellbore noise logging for solving practical problems in wells of various categories. Aims and Objectives Lab experimental study devoted to investigating the nature of acoustic noise spectral characteristics disturbance in a wellbore mockup with steel casing in presence of the acoustic source behind the casing. Methods The study is performed using the reference high-accuracy hydrophone and a wide frequency band wellbore logging tool at a close to real scale lab wellbore mockup. Results It is established the fact that acoustic resonances appear inside the casing volume with respective disturbances of the original signal that are also affected by the parameters of the specific wellbore tool.

Noise Sources and Spectral Characteristics of the Tip-Jet Driven Rotor

The noise sources of the tip-jet driven rotor are mainly classified as rotor blade noise and jet noise. The rotor blade noise includes thickness noise, loading noise, and nonlinear quadrupole noise, while the jet noise includes nozzle momentum noise and jet radiation noise. Each noise component has different noise source mechanisms related to flow characteristics and the rotating motion. Especially, the nozzle momentum noise has two noise source mechanisms based on the rotating steady aerodynamic load and the nozzle mass flow rate. The details of the time signal and spectrum are discussed to study the unique spectral characteristics. The tip-jet driven rotor noise has both tonal and broadband spectral characteristics. The periodicity of each instance of jet radiation noise is discussed, while the total jet radiation noise also has a tonal noise component. The noise source mechanisms and spectral characteristics are important considerations for an acoustically efficient tip-jet driven rotor.

Vowel and Sibilant Production in Noise: Effects of Noise Frequency and Phonological Similarity.

Purpose This study investigated vowel and sibilant productions in noise to determine whether responses to noise (a) are sensitive to the spectral characteristics of the noise signal and (b) are modulated by the contribution of vowel or sibilant contrasts to word discrimination. Method Vowel and sibilant productions were elicited during serial recall of three-word sequences that were produced in quiet or during exposure to speaker-specific noise signals. These signals either masked a speaker's productions of the sibilants /s/ and /ʃ/ or their productions of the vowels /a/ and /æ/. The contribution of the vowel and sibilant contrasts to word discrimination in a sequence was manipulated by varying the number of times that the target sibilant and vowel pairs occurred in the same word position in each sequence. Results Spectral noise effects were observed for both sibilants and vowels: Responses to noise were larger and/or involved to more acoustic features when the noise signal masked the acoustic characteristics of that phoneme class. Word discrimination effects were limited and consisted of only small increases in vowel duration. Interaction effects between noise and similarity indicated that the phonological similarity of sequences containing both sibilants and/or both vowels influenced articulation in ways not related to speech clarity. Conclusion The findings of this study indicate that sensorimotor control of speech exhibits some sensitivity to noise spectral characteristics. However, productions of sibilants and vowels were not sensitive to their importance in discriminating the words in a sequence. In addition, phonological similarity effects were observed that likely reflected processing demands related to the recall and sequencing of high-similarity words.

Spectral characteristics of noise during hardening of welds of rod structures

The article deals with the task of forming a noise spectrum during the processing of parts by the method of surface plastic deformation using a ball-core hardener. Processing using this method is used to harden both flat and curved surfaces, create compressive residual stresses, smooth out cavities, apply a regular microrelief on friction pairs, and also to process welds. The treatment process is accompanied by a loud noise, which mainly exceeds the standard values in the working area of the operator. The results of experimental studies of the spectra of noise and vibration to ensure acoustic safety are presented. The evaluation of the formation of the sound field in the working area of the sources considered. In the course of experimental studies, hazardous and harmful production factors arising from the implementation of machining welded structures were identified. The results of measuring sound pressure levels at the operator’s workplace during compressor operation and the processing of welds of channels and angles are presented. The obtained data are compared with theoretical conclusions about the laws governing the formation of noise spectra and the contribution of noise sources to the sound field at the operator’s workplace.

Coded Aperture Optimization in Spatial Spectral Compressive Spectral Imagers

The spatial spectral compressive spectral imager (SSCSI) is a recently proposed optical architecture, where the spatial-spectral coding of a scene is jointly realized by a binary ON-OFF mask and a dispersive element. The quality of the recovered hyperspectral scene in SSCSI depends on various parameters, such as the coded aperture location with respect to the sensor, the coded aperture and detector pitch sizes, and the diffraction introduced by the grating. Given these parameters, the sensing matrix of the imager is largely dependent on the coded aperture structure and characteristics. As such, its optimization is critical to maximizing the quality of the recovered scene. In this article, an algorithm that optimizes the coded aperture patterns for SSCSI is derived. The final structure of such patterns turns out to be directly linked to the coded aperture position measured from the sensor. It is also shown that the optimal coded apertures in SSCSI adhere to green-blue noise spectral characteristics, where the degree of green spectral components depends on the location of the coded aperture with respect to the sensor. Simulations under different conditions are presented to demonstrate the underlying concepts.

Improvement of the method of calculating a group of sound­insulating panels

Original single-layer and multilayer structures of sound-insulating panels are considered, as well as their advantages compared to traditional analogs. The shortcomings of the method of optimization calculation of a group of sound-insulating panels designed to reduce noise in several production rooms are analyzed. This method has limited functionality due to a relatively small number of objective functions and the corresponding conditions for their use. Given this, an improved method of optimization calculation of a group of sound-insulating panels is proposed. The improvement of the method consists in increasing the number of objective functions intended for multipurpose optimization taking into account real production conditions. The refinement of the algorithm consists in the preliminary selection of a subgroup of panels with additional requirements for operating conditions (increased strength, fire safety, etc.). Under these conditions, the operator directionally distributes structures and materials among the selected panels. The statement of the optimization problem of group calculation with an extended list of objective functions and restrictions is given. Recommendations on selecting an objective function in specific production conditions are given. The regulatory requirements for noise reduction in production rooms and spectral characteristics of sound insulation of panels made of various materials are given. The spectral characteristics of noise in the room before and after application of the sound-insulating panel are also given. The effectiveness of the method is confirmed by the steady reduction of the mathematical expectation and variance of the total noise load on people in production premises with an increase in the number of iterations. The calculation method demonstrated the reduction of excess noise load in comparison with standard methods