Changes In Sound Pressure Level Research Articles

Vibration Characteristics of Liquid-Filled Pipes Under Different Levels of Submergence

Based on the acousto-solid coupling theory, the vibroacoustic radiation characteristics of the liquid-filled pipeline are studied under different submergence depths, and the changes of sound pressure level of pipeline are analyzed under different submergence depths of the flow transfer pipeline. The vibration characteristics of liquid-filled pipes with different submergence degrees were numerically analyzed from the pressure-acoustic domain and the solid mechanics domain, and the two-way coupled data exchange was realized by using acoustic-structural boundary multi-physical field function. The sound pressure level variation curves of the liquid-filled pipes were calculated for different submergence depths under the simultaneous action of internal and external flow fields, respectively. The results show that when the pipe is submerged in the lower and middle positions of the center of the circle, the sound pressure fluctuations of the pipe radiating outward are more consistent, and when submerged in the upper half, the sound pressure concentration phenomenon occurs in the lower and middle regions outside the pipe. When the free boundary outside the pipe is subjected to the boundary load, the pipe submerged in the lower position of the center of the circle is most obviously affected by the load. The tube submerged in the upper and lower positions of the center of the tube will produce two-way, increasing the form of sound pressure propagation in the tube towards the upper and lower sides, these findings can provide a certain reference for the study of pipe vibroacoustics. Therefore, research on the acoustic radiation properties of liquid-filled pipelines under various submergence depths is of great theoretical significance and engineering application value. This information can be applied widely in the fields of anti-fatigue design, fatigue damage analysis, and safety assessment of oil and gas pipeline structures, providing strong scientific support to ensure their safe and reliable service.

An auditory brain-computer interface to detect changes in sound pressure level for automatic volume control

Volume control is necessary to adjust sound levels for a comfortable audio or video listening experience. This study aims to develop an automatic volume control system based on a brain-computer interface (BCI). We thus focused on a BCI using an auditory oddball paradigm, and conducted two types of experiments. In the first experiment, the participant was asked to pay attention to a target sound where the sound level was high (70 dB) compared with the other sounds (60 dB). The brain activity measured by electroencephalogram showed large positive activity (P300) for the target sound, and classification of the target and nontarget sounds achieved an accuracy of 0.90. The second experiment adopted a two-target paradigm where a low sound level (50 dB) was introduced as the second target sound. P300 was also observed in the second experiment, and a value of 0.76 was obtained for the binary classification of the target and nontarget sounds. Further, we found that better accuracy was observed in large sound levels compared to small ones. These results suggest the possibility of using BCI for automatic volume control; however, it is necessary to improve its accuracy for application in daily life.

Multi-channel active noise reduction system realizes the local area sound field control of the subway driver's cabin

Aerodynamic noise, air conditioning fan noise, and wheel-rail noise during subway operation have an adverse effect on drivers' physical and emotional well-being and can jeopardize the safe operation of vehicles. On the basis of the original passive acoustic treatment, multi-channel active control technology is used to manage the local sound field in order to further enhance the acoustic comfort of subway drivers' working environment. The multi-channel active noise reduction system installed on the driver's seat is described in this paper. In order to properly prevent the issues of ear pain and obstruction brought on by prolonged use of noise-canceling headphones, the system integrates reference sensors, error sensors, speakers, and a power amplifier within the headrest. The noise in the carriage is picked up using a multi-channel reference signal, and a low delay and anti-interference algorithm is investigated in accordance with the wide frequency band's characteristics and the abrupt change in sound pressure level when the vehicle is running. The test results demonstrate the system's ability to stabilize under situations of abrupt changes in driving noise and in-car broadcast, as well as to successfully minimize noise in the head area of subway drivers.

Analysis of Acoustic Flow Field Characteristics of Key Components of High-Speed Train Bogies

In this paper, we aim to address the challenge of airflow interference during fault detection in high-speed train bogies by introducing a flow field and investigating the characteristics of the sound field distribution of critical components under its influence. This approach overcomes the limitation observed in previous studies that ignored the impact of the flow field. Furthermore, we evaluate and compare various layouts for inter-track acoustic sensor arrays. The study results demonstrate that the axle box and gearbox are primarily affected by frequency bands above 200 Hz, while the motor is mainly influenced by frequencies above 150 Hz. Moreover, the motor is most significantly impacted by vehicle speed, followed by the gear box and finally the shaft box. When altering the vibration frequency of the sound source, there is a decreasing trend in minimum sound pressure level with increasing frequency. Additionally, the gradient of the sound pressure level change at three locations (motor, gear box, and axle box) exceeds that of both vehicle speed variation and vibration intensity of the sound source. By adjusting the vibration intensity of the sound source, similar gradients are observed for both maximum and minimum values of sound pressure level at these three locations. Therefore, vibration intensity has a consistent effect on changes in sound pressure level at these three places but only influences its magnitude. The aforementioned methods can be employed for the analysis of wind noise and structural noise, thereby offering novel insights for future advancements in noise reduction processing.

Control of a rectangular impinging jet: Experimental investigation of the flow dynamics and the acoustic field

Passive control techniques of impinging jets are of high interest for many industrial applications and particularly for noise generation issues encountered in such configurations. Thus, an experimental study was carried out to simultaneously show the effect of a mechanism of control on the acoustic and the dynamic fields involved in a rectangular jet of air impinging on a slotted plate. A Reynolds number of Re = 5900 presenting an intense acoustic level was considered. The mechanism of control consists on a thin rod which was introduced in different positions of the flow. A total number of 1085 spatial positions of the rod were tested in order to identify the optimal position for noise reduction. Combined Stereoscopic Particle Image Velocimetry measurements were performed to obtain the kinematic field in the whole area of interest from the both sides of the introduced rod. A new representation of the acoustic levels (cartography of acoustic level as function of the location of the rod) is provided to identify the optimal positions of control. It was found that when the self-sustaining tone loop disappears, the sound pressure levels can drop by almost 23% depending on the location of the rod. A Dynamic Mode Decomposition (DMD) was established and cross-correlations were calculated between temporal modes and acoustic signals for both controlled and not controlled cases. The cross-correlations between the acoustic signal and the temporal modes were found to be insignificant in case of controlled flow. Moreover, in case of controlled flow, spatial modes were found to be significant far from the slot which plays a principal role in the self-sustaining tones by interacting with the passage of vortices through it. These results are of interest since the visualization of the flow dynamics and the corresponding vortex activity explains the disappearance of the self-sustaining loop and the sound pressure level changes. Such results are of high interest for developing new strategies of noise control.

Simulation study on the flow-induced vibration and noise in marine centrifugal pumps

Due to the three-dimensional non-axisymmetric shape of the volute, its interaction with the impeller increases the internal flow field complexity and instability of the marine centrifugal pump, representing the main reason for pump body vibration and hydraulic noise. First, the basic principle of fluid machinery noise calculation was explained based on the Lighthill acoustic analogy method and Curle’s theory. Then, the fluid pressure pulsation and flow characteristics of centrifugal pumps were analyzed using the Fluent software, after which the Actran software was used to examine the flow-induced vibration noise properties. The results showed that the clearance size significantly impacted the pump head, while the peak value of the flow-induced vibration response was mainly twice the blade frequency. Although a larger ring clearance increased the structural vibration, it had little impact on the sound pressure level changes in the external sound field. The results provided a new method for the structural optimization and low-noise design of marine centrifugal pumps.

Acoustic Performance Analysis of Diesel Engine Silencer

The finite element model of diesel engine muffler is established, the noise reduction function of the muffler is studied and tested, the distribution cloud diagram of sound pressure level inside the muffler is calculated, the sound fields at various frequencies are plotted. The change of sound pressure level inside the muffler is tested. After processing, the line spectrum and octave band results of the transmission loss of the muffler are obtained. The acoustic performance of the muffler can be quantitatively determined by synthesizing the results of the sound field distribution and the transmission loss inside the muffler.

The Influence of Urban Green Space Soundscape on the Changes of Citizens’ Emotion: A Case Study of Beijing Urban Parks

Coronavirus disease 2019 has significantly impacted mental health. Urban green spaces’ ecological function can improve citizens’ well-being and mental health; thus, this study explored the value realisation mechanism of ecological products in green space by examining the impact of urban green space soundscape on citizens’ emotions. Additionally, we investigated citizens’ subjective perceptions and emotional changes in soundscape through questionnaires. An A-weighted sound pressure level meter was used to measure the sound pressure levels at three points in a day to obtain the sound pressure level changes during different day periods in a park. Subsequently, the universal conclusion through a comparative analysis of the sound pressure level change in urban parks during the day was roughly ‘M’ shape. Further, a structural equation model analysed the influence of different soundscape on public sentiment and used a multigroup analysis to examine the difference in the impact of natural sounds in summer and winter on the change in public opinion. The results show that natural and living sounds positively affect citizens’ emotions, whereas mechanical sounds negatively affect citizens’ emotions. Furthermore, natural sounds in summer positively affect citizens’ moods significantly. Conversely, natural sounds in winter negatively affect citizens’ attitudes, but this is not obvious. Finally, this study proposed some suggestions for managing and improving urban green space soundscape.

Numerical study on the aerodynamic and acoustic scale effects for high-speed train body and pantograph

Based on computational fluid dynamics (CFD) and Lighthill acoustic analogy theory, the aerodynamics and acoustic scale effects of high-speed train bodies and pantographs are numerically studied, by changing the model scale. The model scales are 1/1, 1/2, 1/4 and 1/8 respectively. The aerodynamic force, flow field behavior, surface pressure and far-field noise of the train body and pantograph models, at different model scales are compared and analyzed. The numerical simulation is in good agreement with the experiment. The reliability of the numerical calculation method has been proven. The results show that as the scale of the model decreases, the root mean square (RMS) value and the degree of fluctuation of the aerodynamic drag coefficient of the pantograph increase. In addition, the aerodynamic drag coefficient of the train body increases, but the degree of fluctuation decreases. The similarity of the unsteady flow field of the pantograph at different model scales is strong, but the similarity of the train body is weak. The main frequency and power spectral density distribution of the pulsating pressure on the surface of the pantograph have obvious corresponding relationships with the model scale, but the train body has no obvious regularity. The longitudinal and lateral propagation characteristics of aerodynamic noise from the train body and pantograph are not affected by the model scale, but the sound pressure level changes. Compared with the train body, the far-field aerodynamic noise of the pantograph is less affected by the model scale. The energy distribution of noise is also affected by the scale of the model. As the model scale decreases, the energy concentration range of radiated noise will change from low frequency to medium high frequency.

On the acoustic performance of double degree of freedom helmholtz resonator based acoustic liners

This study investigates the acoustic performance of double degree of freedom Helmholtz resonators and multi cell acoustic liners made of these resonators, both experimentally and through finite element analysis. The dimensions of the resonator internal cavities were varied to assess the effect of the volume ratio on the acoustic performance of the system. Experiments were performed using a grazing flow impedance tube and instrumented 3D printed modular resonators, which can be switched between a single and double degree of freedom resonating cavity configuration. An aluminium acoustic liner with 16 modular resonating cavities was also used in experiments. The effect of the volume ratio is investigated by presenting the transmission loss and transmission coefficient induced and the changes in sound pressure level within the resonator. The underlying sound attenuation mechanisms are further elaborated through the finite element analysis results of the acoustic pressure and velocity fields in the different resonator configurations. The results showed that as the volume ratio is increased, the difference between the first and second resonance frequencies tends to have a convex behaviour. This may indicate the presence of an optimum volume ratio of the two internal cavities for a broad bandwidth of sound absorption. Moreover, the finite element analysis results showed that increasing the volume ratio increased both the transmission loss induced and the bandwidth of frequencies attenuated at the first resonance frequency due to an in-phase velocity magnitude relation, for both the neck and septum of the resonator. Conversely, for the second resonance frequency, there is an out-of-phase relation between the neck and septum velocity magnitudes. In addition to the single resonator analysis, the acoustic performance of liner configurations with 16 resonators was also investigated. The results showed an increase in the bandwidth of attenuated frequencies when each resonating cavity had a different volume ratio, as compared to a fixed volume ratio. In addition, the order of the resonators of different volume ratio in the liner arrangement did not seem to have a significant effect on the overall sound attenuation performance.

Standard sample evaluation method for noise annoyance suppression from audio injection

Noise control technology based on sound energy reduction uses sound pressure level as an evaluation index, and the addition control technology proposed in recent years uses annoyance as an evaluation index. However, no method has been proposed to link the change in sound pressure level with the change in annoyance. In this paper, three types of transformer substation noise are selected as the target sounds, natural sounds and synthetic sounds are selected as the controllable sound, and the pure tone annoyance and combined noise annoyance evaluation experiments are carried out using the standard sample method, and the curve of the decrease value of annoyance and the equivalent sound pressure level change value is obtained. And the effect of audio injection annoyance control is quantitatively analyzed, aiming to build a bridge between addition control and subtraction control. The research results show the effect of controllable sound on the annoyance of substation noise. This study provides new ideas for quantitative analysis of noise control effects and substation noise control.

Monitoring spatial and temporal soundscape features within ecologically significant U.S. National Marine Sanctuaries.

The U.S. National Oceanic and Atmospheric Administration's Office of National Marine Sanctuaries manages a system of marine protected areas encompassing more than 2,000,000 km2 . U.S. National Marine Sanctuaries (NMS) have been designated to provide protection for their conservation, recreational, ecological, historical, scientific, cultural, archaeological, educational, or aesthetic qualities. Due to the large variability of attributes among NMS, designing coordinated system-wide monitoring to support diverse resource protection goals can be challenging. Underwater sound monitoring is seeing increasing application to marine protected area management because it is able to support this wide variety of information needs. Passive acoustics are providing invaluable autonomous information regarding habitat associations, identifying species spatial and temporal use, and highlighting patterns in conditions that are otherwise difficult to survey. Using standardized equipment and analysis methods this study collected ambient underwater sound data and derived measurements to investigate temporal changes in sound pressure levels and power spectral density, identify presence of select species of importance and support within and among site comparison of ambient underwater sound among eight sites within four U.S. NMS. Broadband sound pressure levels of ambient sound (10-24,000 Hz) varied as much as 24 dB re 1 µPa (max difference 100-124 dB re 1 µPa) among the recording sites, sanctuaries, and seasons. Biotic signals, such as snapping shrimp snaps and vocalizations of fishes, exhibited distinct diel and seasonal patterns and showed variation among sites. Presence of anthropogenic signals, such as vessel passage, also varied substantially among sites, ranging from on average 1.6-21.8 h/d. The study identified measurements that effectively summarized baseline soundscape attributes and prioritized future opportunities for integrating non-acoustic and acoustic variables in order to inform area-specific management questions within four ecologically varying U.S. National Marine Sanctuaries.

Listening to cities during the COVID-19 lockdown: How do human activities and urbanization impact soundscapes in Colombia?

Noise is one of the fastest growing and most ubiquitous type of environmental pollution, with prevalence in cities. The COVID-19 confinement in 2020 in Colombia led to a reduction in human activities and their associated noise. We used this unique opportunity to measure the impacts of noise on urban soundscapes, and explore the effects of urbanization intensity independently of human activity. We launched a community science initiative inviting participants to collect audio recordings from their windows using smartphones. Recordings were taken during severe mobility restrictions (April), and during a period of lightened restrictions (May–June). From the data collected, we measured changes in sound pressure levels (SPL), acoustic structure (soundscape spectro-temporal characteristics), and human perception between the two periods. A 12% increase in human activities had a detectable acoustic footprint, with a significant increase of SPL (2.15 dB, 128% increase), a shift towards dominance of low-frequency broadband signals, and a perceived dominance of human-made over wildlife sounds. Measured changes in SPL and acoustic structure were directly proportional to urbanization; however, perception of these changes was not. This gap may be associated with a masking effect generated by noise or a disconnect of humans from nature in large cities. The mobility restrictions created a chance to better understand the impacts of urbanization and human activities on the soundscape, while raising public awareness regarding noise pollution effects on people and wildlife. Information analyzed here might serve in urban planning in developing countries where urban expansion is occurring in a rapid, unplanned fashion.

Sound Pressure Distribution of Car Interior and Influence of Wall

In order to analyze how the sound emitted from the speaker of the car changes due to the influence of the wall, in the case of a box of rectangular parallelepiped (internal dimension 600 mm × 600 mm × 630 mm) with or without sound absorbing material (glass wool with a thickness of 50 mm) Experiments and calculations using the FE model were performed. The calculation results were able to reproduce the experimental results. It was also confirmed that the sound pressure level changes by about 20 dB above 500 Hz with and without glass wool. Next, we created a simple FE model that simulates the interior of an automobile, and the effect of sound absorption on the ceiling and floor, and the sound pressure level and sound pressure distribution when a sound absorbing material (PET material with a thickness of 50 mm)was added. The change of was measured using a real vehicle (Lexus UX) and analyzed by the FE model. It was confirmed that there was a difference in the sound pressure distribution from 100 Hz with and without PET.

The Auditory Mechanics of the Outer Ear of the Bush Cricket: A Numerical Approach

Bush crickets have tympanal ears located in the forelegs. Their ears are elaborate, as they have outer-, middle-, and inner-ear components. The outer ear comprises an air-filled tube derived from the respiratory trachea, the acoustic trachea (AT), which transfers sound from the mesothoracic acoustic spiracle to the internal side of the ear drums in the legs. A key feature of the AT is its capacity to reduce the velocity of sound propagation and alter the acoustic driving forces of the tympanum (the ear drum), producing differences in sound pressure and time between the left and right sides, therefore aiding the directional hearing of the animal. It has been demonstrated experimentally that the tracheal sound transmission generates a gain of ∼15 dB and a propagation velocity of 255 ms−1, an approximately 25% reduction from free-field propagation. However, the mechanism responsible for this change in sound pressure level and velocity remains elusive. In this study, we investigate the mechanical processes behind the sound pressure gain in the AT by numerically modeling the tracheal acoustic behavior using the finite-element method and real three-dimensional geometries of the tracheae of the bush cricket Copiphora gorgonensis. Taking into account the thermoviscous acoustic-shell interaction on the propagation of sound, we analyze the effects of the horn-shaped domain, material properties of the tracheal wall, and the thermal processes on the change in sound pressure level in the AT. Through the numerical results obtained, it is discerned that the tracheal geometry is the main factor contributing to the observed pressure gain.

Some trends and features in deep-ocean noise determined from the CTBTO hydroacoustc stations

This paper describes the results of applying s statistical method for long term and seasonal trend analysis and uncertainty evaluation of the data from deep-ocean noise data. The analysis method uses a flexible discrete model that incorporates terms that capture seasonal variations in the data together with a moving-average statistical model to describe the serial correlation of residual deviations, with uncertainties validated using bootstrap resampling.The measured data originate from a number of the hydro-acoustic monitoring stations of the CTBTO and span up to a maximum of 15 years. The analysis focuses on the data from Cape Leeuwin Southern Ocean), Wake Island (Pacific Ocean), Ascension Island (Atlantic Ocean), and Diego Garcia (Indian Ocean). The trend analysis is applied to time series representing monthly and daily aggregated statistical levels for five frequency bands to obtain estimates for the change in sound pressure level with associated coverage intervals. The features of the data are described, including the differences observed in the seasonal variation and the long-term trends, with the latter often exhibiting negative gradients. A tentative discussion is initiated of the potential causes of some of the observed trends and fluctuations.

Assessing the Possibilities of Identifying Bowhead Whales on the Arctic Shelf

Real recordings of bowhead whale signals and numerical simulation were used to investigate the propagation of such signals in an Arctic-type shallow-water waveguide. The authors analyzed attenuation and distortion of whale signals with increasing distance in the following conditions: (1) a soft and hard bottom, (2) different whale depths, (3) surface waves, (4) additive noise, and (5) reception by a single hydrophone and a vertical array. Signal attenuation was estimated by the change in sound pressure level (SPL). Signal distortion was estimated by the change in the correlation coefficient for the spectrograms of received signals and the reference spectrograms. It is shown that, compared to signals from a single receiver, the attenuation and distortion characteristics of the array output signals are more stable and resistant to changes in whale depth, to possible, under Arctic conditions, significant variations in sound speed in the bottom along the acoustic path, and to the effects of additive noise. The results can be used for passive monitoring of bowhead whales on the Arctic shelf.

Temperature-Activated Change of Permeable Material Properties for Low-Noise Trailing Edge Applications

The present work analyses broadband noise scattering from permeable trailing edges with identical micro-structure but under a change of temperature. Experiments are performed in an anechoic wind tunnel using a NACA0018 airfoil at chord-based Reynolds numbers between 1.88 × 105 and 3.14 × 105 and no incidence. A microphone array is used to determine far-field sound pressure level changes upon trailing edge heating. It is found that broadband noise emission can be actively controlled by varying the temperature of the porous trailing edge inserts. Specifically, the electrically heated inserts yield a noise level variation of up to 2.5 dB with the heated one being noisier compared to a baseline, unheated material with similar micro-structure. Resistivity measurements of permeable samples with varying temperature show that flow resistivity increases with the fluid temperature which is in agreement with the reported trailing edge noise increase.

A statistical method for the evaluation of long term trends in underwater noise measurements.

Deep ocean ambient sound levels have been the subject of recent studies, with particular interest in the identification of long term trends. This paper describes a statistical method for performing long term trend analysis and uncertainty evaluation of the estimated trends. Uncertainties are needed if the quality of the estimates are to be assessed and if the results from different studies or different methods are to be compared. The measured data span 14 years, from 2003 to 2017, and originate from the Southern Ocean close to Cape Leeuwin, Australia. The method uses a flexible discrete model incorporating terms that capture seasonal variations in the data and a moving-average statistical model to describe the serial correlation of residual deviations, with uncertainties validated using bootstrap resampling. The method is applied to time series representing monthly and daily aggregated statistical levels for five frequency bands to obtain estimates for the change in sound pressure level over the examined period with associated uncertainties. The results show a statistically significant reduction in sound pressure levels over the examined period at that location. Possible explanations for these changes are postulated, including the effects of shipping, wind speed, sea surface temperature, and changes in Antarctic ice volume.

Effects of Different Spectral Shapes and Amplitude Modulation of Broadband Noise on Annoyance Reactions in a Controlled Listening Experiment.

Environmental noise from transportation or industrial infrastructure typically has a broad frequency range. Different sources may have disparate acoustical characteristics, which may in turn affect noise annoyance. However, knowledge of the relative contribution of the different acoustical characteristics of broadband noise to annoyance is still scarce. In this study, the subjectively perceived short-term (acute) annoyance reactions to different broadband sounds (namely, realistic outdoor wind turbine and artificial, generic sounds) at 40 dBA were investigated in a controlled laboratory listening experiment. Combined with the factorial design of the experiment, the sounds allowed for separation of the effects of three acoustical characteristics on annoyance, namely, spectral shape, depth of periodic amplitude modulation (AM), and occurrence (or absence) of random AM. Fifty-two participants rated their annoyance with the sounds. Annoyance increased with increasing energy content in the low-frequency range as well as with depth of periodic AM, and was higher in situations with random AM than without. Similar annoyance changes would be evoked by sound pressure level changes of up to 8 dB. The results suggest that besides standard sound pressure level metrics, other acoustical characteristics of (broadband) noise should also be considered in environmental impact assessments, e.g., in the context of wind turbine installations.