Amount Of Noise Reduction Research Articles

Аналіз конструкцій глушників вакуумних насосів

The substantiation of the structural and functional scheme of the muffler filter of the rotary vane vacuum pump, which has the ability to separate oil from air and collect it for further processing, has been completed. The proposed design, due to its design feature, provides sound suppression, reduces noise and has minimal resistance to the movement of the air flow in the middle of the muffler filter. The muffler filter is based on the fact that air, together with the oil that lubricates the vacuum pump nodes, enters the muffler filter through the inlet pipe at a speed of 11...16 m/s, which allows the most complete separation of oil from air. The trajectory of the movement of air in the muffler is described by a helical winding, and therefore, centrifugal force acts on the oil particles in a suspended state, as a result of which the oil particles are thrown to the sieve catcher, the oil is separated from the air and enters the interwall space of the housing and the sieve catcher, and flows down into the oil sump, from where it is drained using a tap. After that, it can be sent for processing, or, after cleaning, enter the pump lubrication system. The oil-free air continues to move over the surface of the screw winding, and due to the change in the pitch of the screw winding, the air decreases its speed, as a result of which the noise level decreases and oil content is cleaned more efficiently. Air passes to the top cover and enters the environment through the outlet pipe. The work establishes a relationship between the pump performance and the design parameters of the muffler filter. In production conditions, it was investigated that the separation of oil from air in the proposed muffler is 93-95%, and the amount of noise reduction is 15-22 dB. The use of a muffler filter implies a decrease in the productivity of the vacuum pump, which is about 1 m3/h, compared to the serial one - 1.28 m3/h. To introduce the muffler filter into production, it is advisable to use the relationship between the performance of the vacuum pump and the structural parameters of the muffler filter and to develop a division into standard sizes.

Modular reverse design of acoustic metamaterial and sound barrier engineering applications: High ventilation and broadband sound insulation

A multi-gradient cavity acoustic metamaterial (MCAM) structure and a modular reverse design method (MRDM) that can realize high ventilation and broadband acoustic isolation are proposed. The method controls the deep neural network model of acoustic metamaterials through a particle swarm algorithm, and the optimized multi-gradient cavity acoustic metamaterial structure (OMCAM) can be reverse-designed by inputting only the constraints and the objective function such as the amount of noise reduction. Compared with the finite element method, the computational efficiency can be improved by about 500 times to achieve an optimized design. The acoustic simulation results show that the average noise reduction of the structure is 23.5 dB in the range of 0∼4000 Hz, and a broadband sound attenuation with 38 dB noise reduction is formed in the target frequency band of 500Hz∼2000 Hz. The acoustic experimental results of the 3D-printed structure are in agreement with the simulation results. Compared with the two existing ventilated acoustic metamaterials, the average noise reduction of OMCAM under equal ventilation capacity is improved by 10.6 dB and 17.4 dB, respectively. The sound barrier based on the proposed OMCAM design is implemented on an elevated rail transit line, showing an improvement of 9.4 dB of average noise reduction compared with existing upright railroad sound barriers. The noise reduction mechanism of the OMCAM structure was finally revealed by the sound field distribution in different modes.

Fan Noise Reduction by Acoustic Liners Combined with Fine-Perforated-Film: Noise Tests by a Small Turbofan Engine DGEN 380

Resonant-type liner panels are one the primary countermeasures for the fan noise of aircraft engines, though the sound absorption performances of the liners are known to be tolerated by the grazing flow streaming on their surface. Therefore, suppressing the effect of the flow on the liners is greatly important for higher sound absorption efficiency. In this study, liner panels with special surface structures were manufactured and applied to an outdoor test using a small turbofan engine, DGEN 380. A special thin film, Fine-Perforated-Film (FPF), was applied to two liner samples. In the first sample, FPF was applied directly to the surface of a typical liner. In the second sample, a gap was fixed between the FPF and liner surface. In addition, a rigid wall and a typical liner were used for comparison, to investigate the effect of the structures. During the test, the samples were installed to the exhaust bypass duct of the DGEN engine. The acoustic pressure inside the duct and in far field was measured. Analysis and comparison of the results showed that the new structures suppressed the effect of the grazing flow and caused a larger amount of noise reduction, compared to the typical liner sample.

Acoustic Characteristics of Rectangular Hypersonic Mixer Ejector

JAXA is currently studying the pre-cooled turbojet engine (PCTJ) to be installed in a hypersonic transport. As a device to reduce exhaust noise at takeoff, a mixer-ejector that is applicable to a rectangular hypersonic nozzle having a complicated geometry with an external ramp has been proposed and tested. The ejector introduces the low-speed secondary flow into the high-speed main jet and reduces the exhaust velocity by mixing. As a result, the mean jet velocity decreases and the jet noise decreases. A 1%-scale mixer-ejector was fabricated, and the mixing process between the main jet and the secondary flow was visualized using Mie scattering of water droplets. The direct relationship between the degree of mixing and the amount of noise reduction was investigated.

Noise reduction in power looms using nitrile rubber polymer

Noise pollution is major concern in textile industries. The excessive noise creates harmful effects on workers, working textile industries. This research paper presents reduction of noise in textile power loom with use of nitrile rubber as damper to reduce noise. The nitrile rubber has hardness value of 50 shore A. The noise is measured employing M370 Electret- microphone. Frequency and time response curves were obtained using Fast Fourier analyzer. From the frequency response in turn found attributes like sound pressure level, sound levels. The parameter such as Permissible Noise Exposure and Noise Exposure Dosage (NED) were determined. The amount of noise reduction were determined using NED. The use of damper provides the noise reduction in textile power loom.

Experimental investigation of NACA-0012 airfoil instability noise with sawtooth trailing edges

This study presents an experimental study of the effect of sawtooth trailing-edge serrations on airfoil instability noise. The far-field noise measurements are obtained to investigate the noise radiation characteristics of a NACA-0012 airfoil operated at various angles of attack: 0°, 5°, and 10°, and covered Reynolds numbers of 2.87 × 105, 3.71 × 105, and 5 × 105. It is found that as the Reynolds number increases, the instability noise shifts from tonal to broadband, whereas as the angle of attack increases, it shifts from broadband to tonal. Furthermore, sawtooth trailing-edges are used to minimize instability tonal noise, leading to considerable self-noise reduction. Parametric studies of the serration amplitude 2 h and streamwise wavelength λ are performed to understand the effect of sawtooth trailing-edges on noise reduction. It is observed that the sound pressure reduction level is sensitive to both the amplitude and streamwise wavelength. Overall, the sawtooth trailing-edge with larger amplitude and smaller wavelength produce the greatest amount of noise reduction.

A reactive hydrodynamic simulation of noise propagation for a concrete-confined detonation

When a point source detonation occurs, high temperature and pressure gases are released and then propagate through the open atmosphere as a blast wave. This leads to an explosive sound in the form of environmental noise, which has been known to cause hearing damage to nearby residents surrounding the explosion area. In an effort to reduce such noise levels, explosion test sites are installed with sound barriers to mitigate and minimize the noise associated with the blasts. In this study, realistic explosion pressure was calculated at an initial detonation source inside a concrete sound barrier, and a numerical prediction was made to evaluate the environmental noise propagation in an actual terrain. In particular, we applied the concrete equation of state to the governing conservation equations for a spherical detonation in a confined geometry and compared the experimental data taken within 3 m from the test site and a few kilometers away from the sound source. Moreover, the amount of noise reduction was predicted by first considering the absorbed explosion pressure by the sound barrier, which later dissipated at a far distance at which the noise propagation in an actual terrain was compared with the measurements.

On the compromise between noise reduction and speech/noise spatial information preservation in binaural speech enhancement.

Spatial information is important for human perception of speech and sound signals. However, this information is often either distorted or completely neglected in noise reduction because it is challenging, to say the least, to achieve optimal noise reduction and accurate spatial information preservation at the same time. This paper studies the problem of binaural speech enhancement. By jointly diagonalizing the speech and noise correlation matrices, we present a method to construct the noise reduction filter as a linear combination of different eigenvectors, which span a certain subspace of the entire space. A different dimension of the subspace gives a different trade-off between noise reduction and speech/noise spatial information preservation. On the one side, if the dimension is equal to 1, maximum noise reduction is achieved but at the price of significant spatial information distortion. On the other extreme, if the dimension of the subspace is equal to that of the entire space, spatial information is accurately preserved but at the cost of no noise reduction. Therefore, one can achieve different levels of compromises between the amount of noise reduction and the level of speech/noise spatial information preservation by adjusting the dimension of the used subspace.

On the effects of anisotropic turbulence on leading edge noise

This paper presents an investigation on the broadband noise produced by the interaction of anisotropic turbulence with isolated aerofoils. Computational aeroacoustic simulations are performed using a synthetic turbulence method with a linearised Euler solver. A comprehensive and fundamental parameter study on leading edge noise is presented to assess the effects of aerofoil thickness, mean flow Mach number, and angle of attack in the presence of moderately anisotropic turbulence. To this end, the streamwise-to-transverse length scale ratio is varied from 0.33 to 3, which can be representative of the anisotropy in the fan wakes from aero-engines, grid-generated turbulence in open-jet wind tunnel experiments, and rotors ingesting turbulent boundary layers. Anisotropic turbulence presents a significant redistribution of the energy in the turbulence spectra in comparison with an isotropic baseline, which affects the resulting noise spectra. It has been found that the noise spectra are mainly influenced by the transverse velocity component for the examined anisotropic flows. The frequency at which the noise spectrum is at a maximum only relies on the mean flow speed and the axial length scale of the anisotropic turbulent flow. Noise reduction due to aerofoil thickness at high frequencies follows a linear trend, but the amount of noise reduction is sensitive to the anisotropy in the flow. It is shown that the contribution of the streamwise disturbances and length scale become increasingly important for thick aerofoils at high Mach numbers and for aerofoils at non-zero angle of attack.

풍력발전기 톱니형 뒷전 블레이드 소음 예측 기법

The reduction of noise from wind turbines has been studied using various methods. Some examples include controlling wind turbine blades, designing low-noise-emitting wind turbine blades, and using trailing-edge serrations. Among these methods, serration is considered an effective noise reduction method. Various studies have aimed to understand the effects of trailing-edge serration parameters. Most studies, however, have focused on fixed-wing concepts, and few have analyzed noise reduction or developed a prediction method for rotor-type blades. Herein, a noise prediction method, composed of two noise prediction methods for a wind turbine with trailing-edge serrations, is proposed. From the flow information obtained by an in-house program (WINFAS), the noise from non-serrated blades is calculated by turbulent ingestion noise and airfoil self-noise prediction methods. The degree of noise reduction caused by the trailing-edge serrations is predicted in the frequency domain by Lyu’s method. The amount of noise reduction is subtracted from the predicted result of the non-serrated blade and the total reduction of the noise from the rotor blades is calculated.

Phase Differences Based Coherence Filter for Dual-Microphone System

This paper proposes a dual-microphone coherence filter, which based on phase difference of two noisy signals. This method passes, without dirtortion target speaker. In real noisy environment, it’s difficult to get exactly information of condition noise field, especially in complex environment. Therefore a post-filtering, which is a function depends on speech presence probability, is suitable for compact dual-microphone and is adapted in the author's approach. The performance of suggested algorithm proved the stability and efficiency of the algorithm. This approach allows increasing performance of speech enhancement in term of signal-to-noise ratio and the amount of noise reduction. The author intends to continue using phase differences as conditions for different algorithms speech quality improvement under various noise conditions.

Technical Note: Impact on central frequency and noise magnitude ratios by advanced CT image reconstruction techniques.

We use central frequency ratio and noise magnitude ratio from noise power spectrum (NPS) to evaluate the noise reduction techniques of ASiR and ASiR-V of GE, SAFIRE and ADMIRE of Siemens, and PixelShine of AlgoMedica. ASiR, ASiR-V, SAFIRE and ADMIRE use a combination of image and projection data whereas PixelShine uses artificial intelligence neural network for noise reduction. The homogeneous module of the ACR computed tomography (CT) phantom was scanned on a GE Revolution HD 64-slice CT for ASiR and ASiR-V, a Siemens Somatom Force for ADMIRE, and a Siemens Definition AS 64-slice for SAFIRE for NPS calculation. The baseline filtered back-projection (FBP) reconstructions were derived from the standard kernel on Revolution HD, Hr44f on Force and D40s on Definition AS. The central frequency ratio (CFR) indicates the degree of shift in the central frequency of NPS after noise reduction. A smaller CFR means a larger shift of the NPS curve, or a larger degree of image blurring. The noise magnitude ratio (NMR) indicates the amount of noise removed. A smaller NMR means a larger degree of noise reduction. An ideal noise reduction shall maintain a CFR close to 1 and a NMR close to 0. The ideal noise reduction by increasing radiation exposure did not shift the central frequency when the image noise was reduced. PixelShine was the closest to the ideal noise reduction in CFR, and was followed by SAFIRE, ASiR-V, ADMIRE and ASiR, in sequence. Similarly, PixelShine had the smallest NMR, and was followed by SAFIRE, ASiR-V, ADMIRE and ASiR in sequence. Overall, PixelShine had the least central frequency shift for the same amount of noise reduction or the most noise reduction for the same amount of central frequency shift. For the same CFR, ASiR-V reduced more noise than ASiR; and SAFIRE reduced more noise than ADMIRE. We introduced two new parameters of CFR and NMR from NPS to compare the reconstructions from different manufacturers. PixelShine had the least central frequency shift for the same amount of noise reduction or the most noise reduction for the same amount of central frequency shift. For the same central frequency shift, ASiR-V reduced more noise than ASiR, and SAFIRE reduced more noise than ADMIRE.

Mapping of noise levels made by drilling machines on project x using contour zone method

Project x is an apartment development activities in Tangerang which in the process of construction resulted in the occurrence of noise. Noise is one of the incidents that can be lead to health problems for the surrounding community. Therefore, this research aims to know the spread of noise, the amount of noise reduction that can be reduced by using a hearing protective device and workers’ perceptions of noise against hearing loss. The method used is the contour zone. Data used is the result of noise measurement Project x in the daytime and nighttime conditions. The result obtained is the noise level in the project work area during the daytime in area 1, 2 and 3 with a distance of 2 meters are 97.1 dB, 94.4 dB, 93.9 dB, and length of 4 meters are 94.4 dB, 91.5 dB, 93.0 dB and night measurements at a distance of 2 meters are 102.2 dB, 100.1 dB, 96.5 dB, and length of 4 meters are 94.7 dB, 94.7 dB, 97.4 dB. The calculation of day and night above exceeds the noise threshold value set by the Ministry of Labor which is 85 dB. The perception of the worker with the noise disturbances that occur at The Yukata Project. Using hearing protection devices will reduce the noises, but at nighttime conditions in areas 1 and 2 at a distance of 4 meters, the noise level still exceeds the noise threshold value which has been determined by the ministry of labor.

Evaluating noise suppression methods for recovering the Lombard speech from vocal output in an external noise field

Speech production is affected by noise due to the Lombard effect. The traditional method of investigation is through headphone delivery of noise to allow speech to be recorded in quiet, but this could create an occlusion effect artefact during speech production. It is also not directly applicable when wearing hearing protectors, hearing aids, or other devices due to physical interference by the headphones. In these situations, the Lombard effect needs to be elicited by an external noise field and speech recorded in the presence of noise. This is a more challenging measurement situation, but one that preserves perception of own voice and the surrounding noise in interaction with the hearing device worn. Two methods, direct waveform subtraction and adaptive noise cancellation, were evaluated for suppressing the background noise in the recorded speech..The effects of sound recording configuration on performance was investigated for two microphone types (omnidirectional and directional) at two distances (50 and 25 cm) in different noises and in the presence of real talker’s movement. Results show that the amount of noise reduction with both suppression methods is greater for fluctuating than continuous noises. Overall, the best recording configuration for noise reduction was with the omnidirectional microphone at 25 cm. Pitch extraction, energy level, and objective speech intelligibility and quality measures show that both suppression methods provide adequate noise reduction for SNRs as low as − 10 dB, which is suitable to successfully recover Lombard speech produced in an external noise field with open ears and when wearing hearing protectors.

Non-Monte Carlo Analysis of Low-Frequency Noise: Exposition of Intricate Nonstationary Behavior and Comparison With Legacy Models

Modeling and analysis of low-frequency noise, such as 1/ ${f}$ and burst noise, with time-varying bias conditions is a long-standing open problem in circuit simulation. In this paper, we offer a solution for this problem and present a computational model for low-frequency noise. The merits of our model are twofold. First, it is fully nonstationary. It can represent noise processes with time-varying statistics that are tightly coupled to the circuit variables in a stochastically correct manner. Second, its mathematical structure allows the utilization of well-established, non-Monte Carlo noise analysis techniques which are orders of magnitude faster than their Monte Carlo counterparts. We first provide an overview of our noise model along with the legacy modeling techniques. We verify that, when used with fast non-Monte Carlo analysis methods, our noise model produces results with the same accuracy as computationally laborious Monte Carlo simulations. We then proceed to contrast our nonstationary noise model with the legacy modulated stationary model. As a typical instance, where the results produced by these two models differ significantly due to intricate nonstationary behavior, we analyze the switched biasing technique that was proposed in order to reduce low-frequency noise. As a case study, we examine the 1/ ${f}$ noise behavior in the previously proposed coupled sawtooth oscillator circuit and show that, whereas simulations conducted with the legacy modulated stationary model suggest that no noise reduction is obtainable with switched biasing, our nonstationary noise model predicts the correct amount of noise reduction observed in previously published experimental data.

Modeling the effects of hearing protection on speech recognition as function of noise level and hearing status

The ability to communicate verbally when wearing hearing protectors is an important aspect to consider for compliance in the use of these devices as well as for safety and operational efficiency in the workplace. Speech recognition with hearing protectors is influenced by many factors such as the overall amount of noise reduction, the slope of the attenuation-frequency function and the presence of hearing loss [Giguere and Berger, Int. J. Audiol. 55, S30-S40 (2016)]. Interestingly, results from subjective and modelling studies sometimes show a benefit of using passive hearing protectors on speech recognition in noise compared to unprotected listening, especially with normal-hearing individuals in high-noise levels. The purpose of this modeling study is to further explore the conditions promoting such a facilitative effect of hearing protectors on speech recognition, with a particular attention to the noise level in the environment and the hearing status of the user. This information is important to better...

Speech recognition in noise under hearing protection: A computational study of the combined effects of hearing loss and hearing protector attenuation

Objective: To investigate the effects of hearing protection on speech recognition in noise. Design: Computational study using a speech recognition model that was previously empirically validated. Study sample: Recognition scores were calculated in unprotected and protected conditions for four sets of hearing protector attenuation functions in two different noises, for three simulated hearing profiles illustrative of those anticipated in the noisy workplace. Results: For a normal-hearing profile, recognition scores were not sensitive to the slope of the attenuation function and the overall amount of noise reduction, but protected conditions provided a small but consistent 7–12% benefit compared to unprotected listening. For profiles simulating hearing loss, recognition scores were much more sensitive to the attenuation function. Substantial drops of 30% or more were found compared to unprotected listening in some conditions of steep attenuation slopes and large noise reductions. Attenuation functions modelled from real hearing protectors with nearly-flat attenuation yielded a benefit compared to unprotected listening for all hearing profiles studied. These findings were true in both noises. Conclusions: Limiting the slope of the hearing protector attenuation function and/or the overall amount of noise reduction is useful and warranted for workers with hearing loss to prevent adverse effects on speech recognition.

Simulation Analysis and Experiment Research on Vehicle Interior Adaptive Active Noise Control System

In the MATLAB/Simulink environment through the simulation analysis, has determined the NFXLMS algorithm of the filter order and the convergence factor control parameters in the vehicle adaptive active noise control system used; adaptive active interior noise control system was constructed in a light bus, the tested vehicle engine was conducted noise cancellation control when its work in 1080rpm and 2400rpm; the results show that, the overall amount of noise reduction of driver's right ear position respectively 9.7dB (Lin) and 8.9dB (Lin).

Advanced modelled iterative reconstruction for abdominal CT: Qualitative and quantitative evaluation

To determine qualitative and quantitative image-quality parameters in abdominal imaging using advanced modelled iterative reconstruction (ADMIRE) with third-generation dual-source 192 section CT. Forty patients undergoing abdominal portal-venous CT at different tube voltage levels (90, 100, 110, and 120 kVp, n = 10 each) and 10 consecutive patients undergoing abdominal non-enhanced low-dose CT (100 kVp, 60 mAs) using a third-generation dual-source 192 section CT machine in the single-source mode were included. Images were reconstructed with filtered back projection (FBP) and ADMIRE (strength levels 1-5). Two blinded, independent readers subjectively determined image noise, artefacts, visibility of small structures, and image contrast, and measured attenuation in the liver, spleen, kidney, muscle, fat, and urinary bladder, and objective image noise. Subjective noise was significantly lower and image contrast significantly higher for each increasing ADMIRE strength level and also for ADMIRE 1 compared to FBP (all, p < 0.001). No significant differences were found for artefact and visibility ratings among image sets (all, p > 0.05). Attenuation was similar across tube voltage-image datasets in all anatomical regions (all, p > 0.05). Objective noise was significantly lower for each increasing ADMIRE strength level, and for ADMIRE 1 compared to FBP (all, p < 0.001, maximal reduction 53%). Independent predictors of noise were tube voltage (p < 0.05) and current (p < 0.001), diameter (p < 0.05), and reconstruction algorithm (p<0.001); the amount of noise reduction was related only to the reconstruction algorithm (p < 0.001). Abdominal CT using ADMIRE results in an improved image quality with lower image noise as compared with FBP, while the attenuation of various anatomical regions remains constant among reconstruction algorithms.

Adaptive Active Control System of Vehicle Noise Design and Test

According to the vehicle interior low frequency noise existing, vehicle interior adaptive active noise control strategy is established based on the FXLMS algorithm, designed the core circuit module active noise controller, including the vehicle interior noise signal amplification module, a main control unit, audio power amplifier module and power module, completed development of the controller hardware, and programming the control software system; using this system, on vehicle driving conditions vice driver left ear position low frequency noise cancellation control in the steady state, the 8.5 dB (Lin) and 10.2dB (Lin) the amount of noise reduction.