Noise Control Methods Research Articles

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.

Open noise barriers for peri-urban environments

Noise as an environmental pollutant in peri-urban environments has become a constant annoyance. Implementing noise-reducing elements to solve this problem is necessary to mitigate noise nuisance and promote the quality of daily life in these areas. This project analyses using trees as scattering elements, using the typology of acoustic barriers based on sonic crystals. Different tree configurations are analyzed using numerical models to determine their effectiveness in scatter sound and absorption, complemented with field studies to validate the models. The results show that specific arrangements and species combinations can significantly reduce noise, proposing a sustainable and aesthetically pleasing solution for noise mitigation in peri-urban areas. This approach offers an effective method of noise control and contributes to the improvement of the ecosystem surrounding these populated areas. Integrating acoustic engineering and ecology principles in this study opens new perspectives in the design of noise barriers, marking a milestone in the search for innovative and environmentally friendly solutions.

Reducing construction noise: sound masking effect on soundscape dominated by construction noise

AbstractPeople move to cities to enjoy the conveniences of modern life, but the resulting population growth comes with issues such as increased noise. While public awareness of noise pollution is increasing, noise emanating from construction sites remains a source of complaint. Despite the actions taken by different parties to control construction noise, newly constructed structures continue to exacerbate the harmful consequences of noise. The acoustic environment in some areas of cities, such as London, can no longer provide the tranquility expected by residents, and the risk of daily disruptions for those living near construction sites is high. Given the various limitations and complications of current construction noise control methods, the campaign to limit construction noise must embrace other strategies. Sound masking can potentially abate noise without resorting to time-consuming procedures. In this paper, five raw construction noise datasets were collected around an existing noise-sensitive premise. Five masker sound datasets were recorded to form seven mixed sounds to create a comparative experiment on masking construction noise. A case study and additional research are presented to demonstrate the mechanism of sound masking and to investigate the factors involved in effectively masking construction noise using the sound masking concept. Based on the case study and theoretical research findings, suggestions for masker selection of specific noise datasets and conclusions regarding ideal sound simultaneous masking of construction noise are provided.

Composite sub-wavelength acoustic metasurfaces for acoustic mode attenuation

This paper reports an experimental investigation of a phase-gradient acoustic metasurface for duct acoustic applications, to evaluate the potential for attenuating acoustic modes and to understand the associated mechanism. The metasurface is a composite configuration where melamine foam as the main part includes a tunable wall. Given a target sound-absorbing frequency, a deeply sub-wavelength metasurface with a thickness-to-wavelength ratio of 1/6.86 is achieved. The unique way of assembling annular metasurfaces offers the possibility of fabricating three different configurations, which are then tested in a duct acoustic rig with artificially generated modes. The performance is assessed through in-duct modal analysis and far-field measurements. The results indicate excellent mode attenuation performance of the designed metasurface at broadband frequencies. The numerical simulation suggests that the mechanism can be related to the conversion from the incident mode to the evanescent waves due to the metasurface. In addition, the effects of the mode suppression are enhanced with the increase of the mode order, which can be attributed to the fact that the performance of the metasurface is influenced by the modal incidence angle. Overall, the present work provides a fascinating noise control method for ducted propulsion systems, and aeroengines in particular.

Application of an improved wide–narrow-band hybrid ANC algorithm in a large commercial vehicle cabine

In recent years, active noise reduction technology has become a research hotspot. However, most active noise reduction technologies are developed based on passenger vehicles and are not implemented in large commercial vehicles. The large commercial vehicle sound field space is large, the traditional active noise reduction method is difficult to implement. In order to explore this problem, this paper proposes an improved active noise control method for commercial vehicles: (1) based on the traditional notch filter, a notch FxLMS algorithm based on speed smoothing is proposed; (2) on the basis of the traditional wire–narrowband hybrid ANC algorithm, the reference signal weighting technology is introduced into the wide-band subsystem, and the notch FxLMS algorithm based on speed smoothing is used as the narrowband subsystem, so as to propose an improved wire-narrowband hybrid ANC algorithm. With the help of MATLAB, the simulation model of the designed algorithm is established, and the collected commercial vehicle test noise data is used as the reference signal to simulate and verify the proposed algorithm. The results show that the proposed method has certain practicability.

Acoustic characteristics of phase-synchronized adjacent propellers.

This experimental study investigates the effect of blade phase angle on noise attenuation in two adjacent, electronically synchronized propellers. Acoustic measurements were performed in an aeroacoustic wind tunnel with a distributed electric propulsion system that involved the adjustment of relative phase angles of 2-bladed propellers between Δψ = 0° and 90°. Ranges of advance ratios (J = 0-0.73) were investigated at a fixed propeller rotation speed of 5000 rpm. The investigation explored the impact on noise directivity and frequency characteristics. The findings reveal significant reductions in noise directivity and tonal noise at the blade pass frequency (BPF). A relative phase angle of Δψ = 90° demonstrated the maximum noise reduction, with an 8 dB decrease at the first BPF and a 2 dB reduction in overall sound pressure level at J = 0. For in-flow conditions (J > 0), a relative phase angle of Δψ = 90° resulted in significant noise reductions of about 24 dB in the first BPF and 6 dB in overall sound pressure level, compared to Δψ = 0°. These observations offer critical insights into the use of the propeller's relative phase angle as an effective noise control method in the distributed electric propulsion system.

Flow and noise control of a cylinder using grooves filled with porous material

In the present numerical study, we propose a new passive flow control mechanism at the Reynolds number of 3900. The novel method benefits from making grooves in the cylinder wall while the grooves are filled with porous materials of a specific permeability. According to the literature survey, while the porous medium is potentially an effective noise control method, it has serious drawbacks, mainly significant pressure drop. In the present study, instead of a porous coating, porous fillers are introduced offering substantial reduction of the noise level, in addition to managing the hydrodynamic parameters. To find a suitable design for the grooves and porous fillers, a systematic parametric study is performed on the number, sequence and size of the grooves, as well as the porous fillers' permeabilities. Based on the results, the newly proposed method dominated the traditional full porous coating by limiting the turbulent kinetic energy (TKE). The results of the parametric study indicated that grooves at an angle of 90° relative to the front stagnation point reduced the overall sound pressure level (OASPL) by 1.25 dB; meanwhile, the high-intensity TKE region shrunk. Further reductions were achieved by deeper grooves and porous fillers, as the drag coefficient, the lift coefficient, the Strouhal number, and the OASPL reduced up to 40.2%, 27.4%, 10.6%, and 3 dB, respectively. The proposed passive control method will be helpful for various industrial applications of cylinders through rigorous control of aerodynamic parameters and the noise level.

An analysis of the “Fast” noise measurements of the dynamic VVER processes

Studies of maneuverable modes of VVER to confirm the possibility of participation of nuclear power plants in the mode of daily carrying capacity have been conducted for quite a long time. Tests at various nuclear power plants with VVER-1000 (Zaporizhzhia NPP in 1998, Khmelnitsky NPP in 2005, Tianwan NPP in 2007) have shown the practical possibility of NPP participation in the daily schedule of carrying capacity, however, the commissioning of nuclear power plants with VVER-1200 requires similar work on all new units with VVER-1200: NVAES-2, LNPP-2 Belarusian NPP. The article presents some aspects of the use of noise control methods for analyzing the condition of equipment and the core. Since the emergence of the technology of noise analysis of signals from VVER reactor installations, researchers have formulated several criteria for obtaining results of appropriate quality. The fundamental requirement for conducting noise experiments was the registration of data in stationary modes of operation of power units, since any non-stationarity made significant changes in spectral estimates, which ultimately complicated the work and “distorted” the results obtained. This requirement was included in the operating instructions of various diagnostic systems using noise signal analysis methods (the SUS system, manufactured by Siemens). For a long period of time, the current situation suited both developers of various diagnostic systems and NPP personnel operating them at power units. On the one hand, this was due to the imperfection of the technical means used (low speed of analog-to-digital converters, limited storage capacity, bulky equipment, etc.), on the other hand, the use of domestic NPP power units only in the base load mode without tracking daily power fluctuations in the power system. The standard archives of the upper block level system, the in-reactor control system and additionally produced multi-channel “fast” measurements with a frequency of 1 kHz for the analysis of maneuverable mode 95-55-95% of the VVER-1200 reactor plant were analyzed. Global disturbances of the core have been detected after one step of the regulatory body of the control and protection system, which attenuates within one second if the next step of the control and protection system has not occurred during this time. Such fast neutron processes can be controlled only by neutron-noise measurements with an upper frequency of at least 20 Hz.

The sound absorption properties of a double-leaf micro perforated panel (DL-MPP) made from a double-layered polypropylene material.

Micro-perforated panel sound absorbers are recognized as an alternative method for noise control, offering advantages over conventional porous absorbers. However, the sound absorption of a single micro-perforated panel (MPP) is limited in its ability to cover a broad range of frequencies, especially in the low-frequency region. Therefore, the primary focus of this study is to investigate the sound absorption performance of a double-leaf micro-perforated panel (DL-MPP) absorber, which aims to achieve high sound absorption across a wide frequency range. This study examines the impact of varying parameters, including perforation ratio, diameter of perforated holes, and air gap thickness, on the sound absorption characteristics of a polypropylene-based DL-MPP absorber. Polypropylene was used as the sound absorption material for this investigation. The DL-MPP absorber consists of two perforated panels installed parallel to a rigid back wall, with an air gap between them. To assess the sound absorption performance, a prototype of the DL-MPP absorber was fabricated and tested using a two-microphone impedance tube method following ASTM E1050 standard. The results demonstrate that the optimal sound absorption performance was achieved by designing the MPPs with a 1% perforation ratio, 1 mm diameter of perforated holes, and a 1 mm sample thickness.

A Study on Assessment of Noise Exposure in the Port Industry: Implications for Occupational Health and Safety

The workplace today is getting more complex, as exposure to chemical, physical, and biological substances at work poses an increasing range of hazards and risks. Industrial hygiene is "that science and art devoted to the anticipation, recognition, evaluation, and control of those environmental factors or stresses arising in or from the workplace". Exposure assessment is the heart of industrial hygiene initiatives, which serves as the foundation for all other functional elements, including medical surveillance, exposure monitoring, engineering controls, administrative controls, and hazardous materials management. Ports are key hubs for worldwide trade, handling a wide range of cargo types with various machinery and equipment. The operational activities within these environments frequently generate high levels of noise, posing a potential hazard to the well-being of the workforce. The purpose of this study is to conduct a comprehensive assessment of noise exposure in the port industry at different locations and to propose appropriate mitigation strategies. The methodology involves the use of sound level measurements using a sound level meter in various port environments. A thorough examination was carried out to identify specific locations for the purpose of conducting noise monitoring. The survey facilitated the quantitative assessment of noise exposure. Based on the findings of this study, necessary recommendations are proposed to minimize noise exposure and protect the well-being of port workers. The insights gained will not just assist port workers but will also contribute to a broader awareness of sustainable and responsible industrial practices. Keywords: Noise exposure, Port industry, Noise assessment, Noise control methods, Personal protective equipment.

Review of Advances in Active Impulsive Noise Control with Focus on Adaptive Algorithms

Mitigating low-frequency noise in various industrial applications often involves the use of the filter-x least mean squares (FxLMS) algorithm, which relies on the mean square error criterion. This algorithm has demonstrated effectiveness in reducing noise induced by Gaussian noise within noise control systems. However, the performance of this algorithm experiences significant degradation and does not converge properly in the presence of impulsive noise. Consequently, to uphold the stability of the ANC system, several robust adaptive algorithms tailored to handle shock noise interference have been introduced. This paper systematically organizes and classifies robust adaptive algorithms designed for impulse noise based on algorithmic criteria, offering valuable insights for the research and application of pertinent active impact noise control methods.

Nonlinear active noise control with tap-decomposed robust volterra filter

The Volterra filter is proven to be a structurally simple method for nonlinear active noise control (NLANC). However, its wide application is deeply constrained by computational complexity. This paper proposes a tap-decomposed Volterra filter, in which a long-tap Volterra filter is approximated as multiple short-tap filters by the nearest Kronecker decomposition. Since the number of taps of decomposed filters is much less than that of the original counterpart, the proposed method greatly reduces the implementation cost of the Volterra filter. Moreover, for impulsive noise sources in NLANC, decomposed filters are updated using the maximum correntropy criterion derived from information theory. Simulation experiments with different noise source types highlight the noise control performance of the proposed approach.

Experimental research on global active rotor noise control using near-field acoustic holography and sound field reproduction

This study employs a 1.6 m diameter rotor to validate the global active noise control method, developed from our previously work, which is based on near-field acoustic holography and sound field reproduction. The validation is conducted through experiments in an anechoic chamber. Additionally, we achieved control over nearly all acoustic modal components of multiple blade passing frequency (BPF) noises of the rotor by extending the time-domain least mean square (LMS) to the acoustic modal domain. The experimental results from near-field acoustic holography revealed that each BPF noise contained 3–4 main acoustic modal components, accounting for almost 90 % of the sound power. The global active noise control experiments demonstrated that the adaptive algorithm in the acoustic modal domain effectively mitigates the influence of rotation speed fluctuations, resulting in steady-state global noise reduction through sound field reproduction. Furthermore, for the first 3 BPF noise, our method achieved noise reduction of 9, 11, and 6 dB by controlling the first 3–4 main acoustic modal components, respectively. The concurrent reduction of various harmonic noises at all observation points validates the method's capability to globally control multiple harmonic noises.

An Empirical noise model of centrifugal fans with different volute tongues based on Langevin regression

In the context of the rapidly evolving field of building ventilation, fan noise control stands out as a pivotal technology to enhance the quality of life. This study aimed to elucidate the inherent randomness, distinct characteristics, and potential low-dimensional noise structure essential for developing effective noise control methods. In this study, a stochastic dynamics model for the noise of centrifugal fans with various volute tongue structures is constructed using the Langevin regression method and experimental measurements. An empirical noise model capturing the peak characteristics of noise discrete tonal is developed through parametric mode expansion and an empirical mean-field model of turbulent wakes, facilitating accurate noise predictions. The research findings demonstrate the effectiveness of the Langevin equation employing the cubic Stuart-Landau equation and multiplicative noise to predict fan noise across different volute tongue structures. While stochastic dynamics models unavoidably lose the characteristic discrete noise peaks, predictions of the total A-weighted sound pressure level remain within a 2.2% error margin. The stochastic dynamics models applied to centrifugal fan aerodynamic noise and turbulent wakes exhibit striking resemblances, suggesting a fundamental connection between turbulence and noise generation. The extended empirical noise model maintains discrete pitch noise peaks by introducing shift modes, indicating that stronger Langevin deformations correspond to larger translational amplitudes of the shift modes. The advancement of stochastic dynamics and empirical noise models lays a foundational framework for the formulation of effective noise control strategies.

A combined method for multi-channel active noise control based on online adaptive estimation and offline convolutional neural network

Multi-channel active noise control (ANC) has been widely used to attenuate low-frequency noise in relatively large spatial areas. Traditional multi-channel systems are achieved by optimizing the controller weights with adaptive algorithms that minimize the power of all error signals. However, nonlinearity in ANC systems can significantly degrade the performance of conventional adaptive algorithms, which is even more severe in multi-channel systems. Researchers suggested using neural networks (NN) to deal with the nonlinear problems. However, applying NN to multi-channelANC systems is challenging in real-time processing because of the high computational burden. Therefore, a multi-channel ANC method that combines NN and adaptive method is proposed. The proposed controller consists of both linear and nonlinear parts, where the linear part is estimated adaptively to track the change of primary noise in real applications while the nonlinear part is modeled offline with a small-scale convolutional NN (CNN). This method has the advantages of solving the nonlinear problem in ANC systems and achieving the capability in tracking primary noise source positions. At last, the performance of the proposed algorithm is verified through simulation experiments.

Active sound transmission reduction across acoustic window

In this study, the experimental method of transfer functions is employed to investigate the possibility of improving the sound transmission loss of acoustic windows using an active control technique. Twenty-five microphones, 20 of them located evenly over the acoustic window's indoor exit (provide error signals) and 5 fixed in the receiver room (capture the transmitted sound), and 19 small loudspeakers were used in the experiments. The loudspeakers acted as the canceling sources, and they were located along the window's interior perimeter (except the bottom part). The receiver room was made relatively “dead” using fiberglass linings. A loudspeaker array located in the source room acted as the primary sound source. The active control is implemented by minimizing the squared sound pressures at selected error microphones. Results show that the active noise control method can improve the sound transmission loss across acoustic window. The performance depends on the arrangement of the cancelling sources and the error microphone locations. It is found that an average of between 6 and 8 dB reduction of sound transmission within the frequency range from 100 to 1000 Hz can be achieved by an active control system with 4 or 6 error microphones and only three cancelling loudspeakers.

Ducted fan noise control by turbulence grids for drones

A small ducted fan with a rotor-stator assembly is being tested in an anechoic chamber at Peking University. To attenuate fan noise, turbulence grids have been inserted before the rotor to eliminate large-scale ingested flow structures and, therefore, to minimize the flow interactions between the rotors and stators. Several different grids with various geometry and solidity configurations have been considered in the tests. To demonstrate the proposed noise control method, both near-field in-duct on-surface microphones and far-field microphones are used to measure acoustic performance. In addition, a microphone array is deployed to acoustic images at several working conditions. The corresponding thrust performance, with and without the grids in between the rotors and stators, is being measured simultaneously. The possible fluid mechanics is presumably caused by the reduced strength of ingested turbulence structures. More results help to reveal this physical understanding will be given in the final manuscript. Through this work, we hope to investigate a new strategy that could possibly reduce UAV fan noise at several representative working conditions.

Low-Frequency Noise Attenuation in a Closed Space Using Adaptive Directivity Control Sources of a Quadrupole Type

A novel method of active noise control using adaptive radiation sound sources is investigated. A finite element model of a modal enclosed sound field is excited harmonically, representing a noise field in the low-frequency range. The control sources are comprised of elementary dipole sources for which the driving signals are adjusted by an optimization method. Two set-up cases of the proposed compound sources are investigated. The coupling of the control sources with the modal sound field is discussed. The simulated performance of the proposed method is compared with that of a system with distributed simple sources and the results show the effectiveness of the sources with adaptive radiation for active noise control in small enclosures.

Design and analysis of experimental adaptive feedback system for active noise control (ANC) in a duct

The limitations of passive noise control methods impose a need for new technical solutions to solve the problem of reducing low-frequency noise, which is considered to be a dominant component of noise disturbance. In recent years, the subject of intensive research are the active noise control systems, which have aroused considerable interest and represent a promising solution to the problem of low-frequency noise control. This paper proposes a robust methodology for simplified design and analysis of an experimental active noise control system for real-time control of acoustic environment in a duct. The proposed feedback control model is based on using the LMS algorithm, combined with FxLMS algorithm for estimation and neutralization of the secondary path in the electro-acoustic system. The study shows the potential of the FPGA module and the Real-time module of cRIO from National Instruments, combined with the LabView software environment when applied in adaptive system for active noise control. The reliability and validity of the developed active noise control system is tested for a frequency range of 100 to 1000 [Hz], by measuring the amplitude-time domain in [V] and sound level in [dB]. The comparison of the experimental results shows great efficiency of the system at lower frequency range from 200 to 400 [Hz], where a maximum reduction in sound level achieved at a frequency of 200 [Hz] is 14 [dB] or 17 [%]. A significant sound level reduction is also achieved at both 300 [Hz] and 400 [Hz] which is 12 % or 10 [dB] in both cases. Given the analysis of the challenges and opportunities of the developed active noise control system, recommendations for advancements and future work are proposed.

Global noise reduction in free-field conditions by using active noise-controlling casings

Active noise control (ANC) methods have been extensively used for reducing the noise level over the past decade. In particular, in the range of low frequencies they can effectively reduce the noise level higher than passive control methods. However, except in some special cases, in ANC only local zones of quiet are obtained. In this paper one of such exceptions is investigated—an active noise-controlling casing. More specifically, a noise source is placed inside the casing. Casing vibrations are actively controlled to achieve global noise reduction in free-field conditions. The global noise reduction is obtained using the Switched Error FXLMS algorithm and using error signals from error microphones located at appropriate points around the casing. It is shown that selected microphone array configurations can provide global noise reduction in free-field conditions. Performance of this approach is experimentally verified in a laboratory room with an exemplary acoustic treatment.