Characteristics Of Sound Sources Research Articles

Study on near-field noise control of stationary equipment

The noise of stationary equipment is usually controlled by the sound insulation shield with the mufflers. However, there is not enough space for the installation of the sound insulation shield in certain places or working conditions, so the noise reduction measures are difficult to apply. The noise control measures at the near-field of stationary equipment, especially those infinitely close to the surface of the equipment, can solve the problem of insufficient installation space. At this time, it is necessary to design a structure of noise control measures to ensure that it have sufficient noise reduction performance. In this paper, a noise reduction structure is designed for near-field noise control of stationary equipment. The experimental results show that the structure have a good noise reduction effect in the certain frequency range. The effective noise reduction frequency can be specially designed according to the frequency characteristics of different sound sources. In addition, a modular installation structure was designed.

Sound source characteristics of heat exchanger under flow conditions

Heat exchangers are the most important equipment in ship cooling system, which generate vibration and noise due to flow excitation during operation, affecting structural safety and having a significant impact on acoustic stealth performance. Mastering the characteristics of sound source has guiding significance for noise reduction design. The acoustic signal directly obtained from the hydrophone inside the pipe including reflected sound wave, which cannot accurately characterize the sound radiation energy from heat exchanger into pipe. In order to accurately evaluate the sound source characteristics of heat exchanger under flow conditions, experimental method was used to test the sound source characteristics of heat exchanger which are not affected by connected pipelines based on the two-port sound source theory. The main factors affecting the sound source characteristics of heat exchanger were analyzed, such as flow rate, background pressure, and temperature. The research can provide reference for the vibration and noise reduction design of heat exchangers.

Numerical simulation study of acoustic source characteristics of liquid level monitor based on infrasound waves

Abstract To investigate the sound source characteristics of infrasound waves generated during the operation of the gas explosion liquid level monitoring instrument, with a focus on the aerodynamic noise produced by the monitoring device, a mixed numerical method was used to simulate and study the impact of different nozzle diameters, gas explosion pressures, and casing pressures on the instrument’s infrasound frequency range. The results indicate that gas explosion pressure, casing pressure, and nozzle diameter primarily affect the spectral characteristics within the 10 Hz to 20 Hz range. As the gas explosion pressure and nozzle diameter increase, the sound pressure level in the internal sound field also increases, and the peak frequency shifts higher. Conversely, with an increase in casing pressure, the sound pressure level in the internal sound field decreases, and the peak frequency shifts lower. The research findings can provide a theoretical basis for the development of the instrument.

Research on the influence mechanism of harmonic components on the noise distribution characteristics of converter transformers

In order to elucidate the sound source characteristics during the noise propagation process of converter transformers, a series of experimental studies were conducted based on finite element simulation and proportional prototype design of converter transformers. It was found that it was unreasonable to equate converter transformers with point sound sources in previous studies. On the contrary, it should be divided into dipole and multipole distribution characteristics. Meanwhile, research has found that the noise distribution of converter transformers exhibits dipole and dipole distribution characteristics under power frequency and harmonic excitation, respectively. The contribution of harmonic components at different frequencies in the formation process of bipolar sound sources was quantified through simulation and experiments, and the key harmonic frequencies for forming multipole sound sources were determined as paired combinations of 5, 7, 11, 13, 23, and 25. Based on the above research conclusions, a noise reduction approach for converter transformers based on bipolar and multipole boundary effects is proposed.

Research on Characteristics of Directional Impulse Sound Sources in a U-shape Connected Well

The traditional U-shaped connected well connection technology mainly relies on the magnetic steering technology to guide the connection of the two wells, but the magnetic steering technology has the disadvantage of short detection distance. In order to increase the detection distance and ensure precise communication between the two wells, a new type of acoustic wave connection technology based on the impulse sound source was proposed in this paper. Firstly, an experimental study on the underwater impulse sound source was conducted and the characteristics of the sound source were analyzed in detail. The results show that the impulse sound source is a wide-band, high-energy, high-conversion efficiency source signal. The research on the sound field characteristics of the U-shaped connected well based on the impulse sound source can accurately locate the azimuth and distance of the target cased well, and provide technical support for guiding the drill bit to connect the target wellbore.

Simulation and experimental study of buried natural gas pipeline leak detection based on sound source characteristics

Buried pipe-line leakage will affect the thermal characteristics of the soil environment, leading to a poor soil environment. In addition, leakage of natural gas possibly produces an explosion and subsequent fire, which has fatal harm. Sustainable detection of underground gas pipe-line leaks is a significant part of current research. In this study, a method for leak detection of buried natural gas polyethylene pipe-lines based on sound source characteristics is investigated. The simulation software was applied in analyzing the variation of leakage rate and sound source in buried pipes under different leakage conditions including mainly different leakage apertures and pipe pressures. Also, an experiment platform was built to verify the simulation results. These results can provide help for gas pipe-line leakage detection and safety protection.

Performance improvement and noise reduction analysis of multi-blade centrifugal fan imitating long-eared owl wing surface

This research was inspired by the long-eared owl's ability to fly silently. For the first time in this study, a wind turbine blade is designed to mimic the wing surface and the leading edge of the long-eared owl. The commonly used two-dimensional blade profile in previous studies is replaced by a more effective three-dimensional profile. This change leads to improved aerodynamic performance of the multi-blade centrifugal fan and reduced noise levels. The airfoil and leading edge profile parameters of the long-eared owl were extracted and utilized. These parameters were used to develop a fitting formula based on their correlation. This formula facilitated the design and optimization of a bionic blade (B-Blade). The results indicate a 4.1% enhancement in the maximum flow rate compared to the original blade fan, alongside a noise reduction of 1.3 dB(A) under identical static pressure conditions. An examination of the internal flow, noise, and sound source characteristics of both fan types was conducted, elucidating the aerodynamic noise mechanism. Fan noise propagation showed pronounced dipole sound source traits. The sound source area at the B-Blade fan's inlet and the volute tongue was more compact, leading to a decrease in mid-low frequency discrete noise. The sound source intensity was also diminished. The B-Blade fan also ameliorated the flow distribution at the impeller outlet, reducing the unstable interaction between the impeller and volute tongue, thereby effectively diminishing noise.

Quasi-real-time estimation of a loudspeaker direction from sound pressure level ratio among four channels

This paper describes a quasi-real-time estimation method of loudspeaker direction under Gaussian noise environment. Our estimation method is based on sound pressure level ratio among four channels when the loudspeaker is surrounded by four microphones. Performance of our method tends to be better when acoustic spatial radiation characteristics of sound source is skewed. Preliminary experiments show that an offline processing version of our method is more than 99% accurate in acoustically clean environments. In this paper, we discuss the noise robustness of our method through simulation experiments. Loudspeaker direction is estimated from 0.34s segments of Japanese sentences every 0.01s, that is quasi-real-time processing. Those segments are contaminated by Gaussian noise at 0dB, 10dB, 20dB. We demonstrate that the proposed method is robust to Gaussian noise. The results show that accuracies of proposed method (Prop2) are 96.9%, 98.2%, 98.4% at the band the center frequency of which is 2000Hz.

Consideration on accuracy on road traffic noise prediction model "ASJ RTN-Model 2018" in power level and equivalent noise level

This paper introduces the study on verification of prediction accuracy about road traffic noise prediction model "ASJ RTN-Model 2018" used as standard for prediction of road traffic noise in Japan. The effects of vehicle type classification, traffic volume and regional characteristics on prediction accuracy were examined for the power level LWA representing the sound source characteristics of the traveling vehicle and the equivalent noise level LAeq of the evaluation value used for noise control standards. As a result, it was confirmed that the prediction accuracy of this model was generally good regardless of the traffic volume, regional characteristics and the vehicle type classification.

A framework for generating large-scale microphone array data for machine learning

The use of machine learning for localization of sound sources from microphone array data has increased rapidly in recent years. Newly developed methods are of great value for hearing aids, speech technologies, smart home systems or engineering acoustics. The existence of openly available data is crucial for the comparability and development of new data-driven methods. However, the literature review reveals a lack of openly available datasets, especially for large microphone arrays. This contribution introduces a framework for generation of acoustic data for machine learning. It implements tools for the reproducible random sampling of virtual measurement scenarios. The framework allows computations on multiple machines, which significantly speeds up the process of data generation. Using the framework, an example of a development dataset for sound source characterization with a 64-channel array is given. A containerized environment running the simulation source code is openly available. The presented approach enables the user to calculate large datasets, to store only the features necessary for training, and to share the source code which is needed to reproduce datasets instead of sharing the data itself. This avoids the problem of distributing large datasets and enables reproducible research.

Orthogonal matching pursuit algorithm based on weighted cosine similarity for sound source localization

Abstract Compressive sensing overcomes the limitations of the Nyquist criteria and is one of the most widely used compressive sensing reconstruction algorithms. Orthogonal matching pursuit (OMP) algorithm is simple, in terms of hardware implementation, and has high computational efficiency. However, the OMP algorithm exhibits poor identification performance for low-frequency sound sources and results in large localization deviations when the mesh spacing of the focus plane is small. In this study, a novel atom selection criterion based on weighted cosine similarity was proposed to improve the OMP algorithm for sound source localization and characterization. This method replaces the original inner product criterion to measure the correlation between the column vectors of the sensing matrix and the residuals, which addresses the atom selection error caused by the high correlation between atoms. Numerical simulations and experimental results show that the proposed method has a stronger anti-noise interference capability and higher accuracy for sound source identification with fewer sampling points, particularly in low-frequency and low signal-to-noise ratio environments. Compared to other OMP algorithms, the proposed method improves the performance of the OMP algorithm in sound source localization and widens the sound frequency range. This study is valuable for achieving highly accurate sound source localization and reducing measurement costs in practical applications.

Laser-plasma sound sources in atmospheric air: A systematic experimental study

Laser-plasma sound sources are increasingly utilized in technological and scientific applications as attractive alternatives to conventional electromechanical or piezoelectric transducers. This work presents a systematic experimental study of laser-plasma sound sources generated in atmospheric air by strong, short and ultrashort laser pulses. Emphasis is given on the dependence of their acoustic emission on the characteristics of the optical radiation. In the experiments, nanosecond and femtosecond laser pulses with different energies and optical wavelengths are focused in atmospheric air using lenses of different focusing power. The produced acoustic pulses are captured via a system with high dynamic range and broad frequency response in the far field of the plasma source. The acoustic signals are analysed both in the time and frequency domains to extract their primary characteristics, particularly the total acoustic energy, peak pressure, spectral magnitude and spectral peak frequency. The results are systematically examined and compared with respect to the characteristics of the exciting laser pulses. The experimental observations are supported by theoretical calculations of the generated plasma density via rate equations that account for the main ionization and electron loss mechanisms. The presented analysis provides a frame for controlling the acoustic characteristics of laser-plasma sound sources, which is particularly important for applications in the fields of acoustic measurements, sound reproduction and biomedicine.

A study on aerodynamic noise characteristics of a high-speed maglev train with a speed of 600 km/h

Purpose This study aims to explore the formation mechanism of aerodynamic noise of a high-speed maglev train and understand the characteristics of dipole and quadrupole sound sources of the maglev train at different speed levels.Design/methodology/approach Based on large eddy simulation (LES) method and Kirchhoff–Ffowcs Williams and Hawkings (K-FWH) equations, the characteristics of dipole and quadrupole sound sources of maglev trains at different speed levels were simulated and analyzed by constructing reasonable penetrable integral surface.Findings The spatial disturbance resulting from the separation of the boundary layer in the streamlined area of the tail car is the source of aerodynamic sound of the maglev train. The dipole sources of the train are mainly distributed around the radio terminals of the head and tail cars of the maglev train, the bottom of the arms of the streamlined parts of the head and tail cars and the nose tip area of the streamlined part of the tail car, and the quadrupole sources are mainly distributed in the wake area. When the train runs at three speed levels of 400, 500 and 600 km·h−1, respectively, the radiated energy of quadrupole source is 62.4%, 63.3% and 71.7%, respectively, which exceeds that of dipole sources.Originality/value This study can help understand the aerodynamic noise characteristics generated by the high-speed maglev train and provide a reference for the optimization design of its aerodynamic shape.

The effects of the natural visual-aural attributes of urban green spaces on human behavior and emotional response.

Nature-based solutions (NBS) have been used to address a wide range of urban environmental challenges, an important aspect of which is to improve human health and well-being. However, most relevant studies focus either on what positive influences nature may have or on identifying what natural factors can have these benefits. Few have investigated the sensory composition of nature and the effects of nature in different sensory aspects on human health. Setting out from the multi-sensory perspective, this study aims to explore human behavior and emotional response from visual and aural contact with urban nature. Taking Jiangjia Art Garden in Chengdu as an example, natural attributes such as its visual (landscape) and aural (sound source) characteristics as well as people's activities (behavioral responses) were measured by on-site mapping analysis. This was done while a questionnaire-based survey was conducted to investigate people's emotional responses regarding their overall satisfaction, pleasantness, calm, and agreeableness. The results indicated that nature-dominated visual landscapes such as grassland, waterscapes, and woodlands, as well as natural sounds such as bird sounds, chirp sounds, and wind sounds were found to be positively correlated to the vitality of activities and people's emotional status. Regarding behavioral responses, it was shown that grasslands and woodlands are more likely to be attractive places for recreation, and the vitality measured became extremely high when these two were paired with lakes. As for the emotional responses, people's perceived overall satisfaction, calm, and agreeableness were equally reflected in their behavioral patterns, suggesting a strong relationship with natural factors. The research findings were visually presented in behavior and emotional maps to provide direct cues of informing the future design of high-quality urban green spaces and promoting the application of aural-visual experience in the design of urban nature areas.

Characterization of sound pressure levels and sound sources in the intensive care unit: a 1 week observational study.

Exposure to elevated sound pressure levels within the intensive care unit is known to negatively affect patient and staff health. In the past, interventions to address this problem have been unsuccessful as there is no conclusive evidence on the severity of each sound source and their role on the overall sound pressure levels. Therefore, the goal of the study was to perform a continuous 1 week recording to characterize the sound pressure levels and identify negative sound sources in this setting. In this prospective, systematic, and quantitative observational study, the sound pressure levels and sound sources were continuously recorded in a mixed medical-surgical intensive care unit over 1 week. Measurements were conducted using four sound level meters and a human observer present in the room noting all sound sources arising from two beds. The mean 8 h sound pressure level was significantly higher during the day (52.01 ± 1.75 dBA) and evening (50.92 ± 1.66 dBA) shifts than during the night shift (47.57 ± 2.23; F(2, 19) = 11.80, p < 0.001). No significant difference was found in the maximum and minimum mean 8 h sound pressure levels between the work shifts. However, there was a significant difference between the two beds in the based on location during the day (F(3, 28) = 3.91, p = 0.0189) and evening (F(3, 24) = 5.66, p = 0.00445) shifts. Cleaning of the patient area, admission and discharge activities, and renal interventions (e.g., dialysis) contributed the most to the overall sound pressure levels, with staff talking occurring most frequently. Our study was able to identify that continuous maintenance of the patient area, patient admission and discharge, and renal interventions were responsible for the greatest contribution to the sound pressure levels. Moreover, while staff talking was not found to significantly contribute to the sound pressure levels, it was found to be the most frequently occurring activity which may indirectly influence patient wellbeing. Overall, identifying these sound sources can have a meaningful impact on patients and staff by identifying targets for future interventions, thus leading to a healthier environment.

A New Method of Identifying the Aerodynamic Dipole Sound Source in the Near Wall Flow

Consider that the sound dipole source in the flow field is composed of multiple micro-spherical oscillating sources. An aerodynamic sound source identification method is established by the relationship among the oscillating source, the radiated sound pressure, and the pressure gradient of flow in the near-wall flow field, and the formula for calculating the sound power of the sound dipole source in unsteady flow is derived. It shows that the power of sound dipole sources is proportional to the square of the oscillating force or pressure gradient. The combination of the formula and CFD method is further applied to the flow around the cylinder, which clearly presents the sound power and location characteristics of sound dipole sources. Further, the relationship between the sound source and the flow separation, or flow vortex shedding, is analyzed. The corresponding correlation analysis is also carried out, which indicates that the sound dipole source exists in a finite area of the attached wall. The front end of the area is at the separation point along the circumferential direction of the wall, and the end is at the location where the separation vortex completely falls off and a trailing vortex begins to form. In addition, the thickness of the area exists along the radial direction and gradually increases backward.

Acoustic-Based Rolling Bearing Fault Diagnosis Using a Co-Prime Circular Microphone Array.

This study proposes a high-efficiency method using a co-prime circular microphone array (CPCMA) for the bearing fault diagnosis, and discusses the acoustic characteristics of three fault-type signals at different rotation speeds. Due to the close positions of various bearing components, radiation sounds are seriously mixed, and it is challenging to separate the fault features. Direction-of-arrival (DOA) estimation can be used to suppress noise and directionally enhance sound sources of interest; however, classical array configurations usually require a large number of microphones to achieve high accuracy. To address this, a CPCMA is introduced to raise the array's degrees of freedom in order to reduce the dependence on the microphone numbers and computation complexity. The estimation of signal parameters via rotational invariance techniques (ESPRIT) applied to a CPCMA can quickly figure out the DOA estimation without any prior knowledge. By using the techniques above, a sound source motion-tracking diagnosis method is proposed according to the movement characteristics of impact sound sources for each fault type. Additionally, more precise frequency spectra are obtained, which are used in combination to determine the fault types and locations.

Compact aerial ultrasonic source integrating the transverse vibration part with the bolt-clamped Langevin transducer

We have previously developed a compact circular vibrating plate aerial ultrasonic source with a grooved uniform rod that can produce a large vibration displacement by using piston vibration and emit intense sound waves perpendicular to the vibration surface. In this paper, to create a compact ultrasonic source that can radiate intense aerial ultrasonic waves, we produced a compact aerial ultrasonic source integrating the transverse vibration part with a bolt-clamped Langevin transducer and we investigated the sound source characteristics. These results demonstrated that compared with a conventional source, the length of our source was shorter, the sound pressure was higher, and its structure was simpler.

Machine learning aided near-field acoustic holography based on equivalent source method.

In recent times, equivalent source method-based near-field acoustic holography methods have been extensively applied in sound source localization and characterization. The most commonly used equivalent sources are spherical harmonics. In a non-reverberant environment with no reflections, these equivalent sources could be the best choice since spherical harmonics are derived for the Sommerfeld boundary condition. However, these methods are not the best fit for reverberating environments. In such cases, a new relationship can be calculated between the field weights and the measured pressure with enough training examples. The proposed machine learning models include linear regression (LR) with adaptive moment estimation (Adam), LR with limited-memory Broyden-Fletcher-Goldfarb-Shanno (L-BFGS), and multi-layer perceptron with one and two hidden layers. These methods are tested for multiple monopoles and vibrating plate simulations in a room with different wall absorption coefficients. The data-driven methods are also studied on loudspeakers numerically and experimentally in a free field environment. The results from these methods are compared with the results of one norm convex optimization (L1CVX). LR with L-BFGS performed the best among all the methods studied and performed better than L1CVX for less absorption coefficient for geometrically separable sources. LR with L-BFGS also has much faster inference times.

Experimental observation of the sound field around a moving source using parallel phase-shifting interferometry

Railway noise is still one of the issues in the wayside environment despite of various countermeasures. For effective countermeasures, it is important to reveal characteristics of sound sources and sound propagation. Using parallel phase-shifting interferometry (PPSI) which measure the air density by interfering the reference light with object light, we tried to observe the sound field around a moving source. This system utilize laser and high-speed camera makes it possible to observe unstedy phenomena and visualize sound waves accurately. As a moving source, a speaker emitting 40kHz sinusoidal sound was mounted on a model, and the model was launched at 100 km/h. As A result, we succeed in observing the sound waves generated from the moving source clearly and visualizing the frequency modulation by Doppler effect. Furthermore, the result was averaged in sub-pixel to understand easily. These results clearly show the difference in frequency depending on the relative position to the sound source as it is in theory.