Increase In Sound Pressure Level Research Articles

Experimental Light Rail Traffic Noise Assessment in a Metropolitan Area

The growth in the utilization and development of rail transport within urban networks is crucial for transitioning towards a more sustainable form of mobility. However, challenges related to discomfort and noise pollution arising from rail traffic must be addressed and mitigated to foster a harmonious coexistence between residents and trains. This study focuses on analyzing an experimental campaign conducted on the surface metropolitan network of Porto to study and identify the frequency content and pressure levels associated with light rail traffic. The presented experimental campaign holds significant relevance as it comprises various and distinct circulation conditions within the railway network, enabling a comprehensive characterization of railway noise. The collected data indicates a noticeable increase in sound pressure levels as the speed of circulation rises, particularly emphasizing the 1/3 octave band centered around 1000 Hz. The choice of tracks with components having a limited capacity for absorbing acoustic energy leads to a significant rise in noise levels compared to track solutions with elements exhibiting excellent acoustic energy absorption. Furthermore, the study highlights a substantial increase in noise levels (10 dBA) associated with small radius curves, even at low speeds. These findings underscore the importance of considering the track characteristics and geometric features in noise assessment within rail networks. Therefore, the insights gained from this experimental campaign contribute significantly to the understanding and comprehensive characterization of railway noise under diverse circulation conditions within the railway network.

Comparisons of aerosol generation across different musical instruments and loudness

Respiratory aerosols can serve as vectors for disease transmission, and aerosol emission is highly activity-dependent. COVID-19 severely impacted the performing arts due to concerns about disease spread by respiratory aerosols and droplets generated during singing and playing musical instruments. Aerosol generation from woodwind and brass performance is less understood compared to singing due to uncertainty about how the diverse range of musical instruments may impact respiratory aerosol concentrations and size distributions. Here, aerosol number and mass concentrations along with size distributions were measured for breathing, speaking, and playing four different woodwind and brass instruments by 23 professional instrumentalists. We find that a 1 dBA increase in sound pressure level corresponds to a ∼10% increase in aerosol number concentration. The aerosol size distribution is consistent with that of breathing. Differences in aerosol emission across musical instruments can be partly explained by the loudness of performance. Measuring aerosol generation from single notes or simple songs may be sufficient to characterise the aerosol emission range during actual performance, provided a range of loudnesses are accessed. These results provide insight into the factors contributing to aerosol emission during musical performance and facilitate risk assessments associated with infectious respiratory disease transmission in the performing arts.

An investigation of the noise characteristics of a small-scale rotor in axial descent

In this work, the acoustic characteristics of a small-scale drone rotor in axial descent are numerically investigated. Various descent speeds covering different working states are tested, and the corresponding effects on the noise are analysed. The turbulent flow fields are obtained using delayed detached eddy simulations and an acoustic-wave preserved artificial compressibility method. The far-field noise is obtained by an integral solution of the Ffowcs-Williams and Hawkings equation. The aerodynamic force and the noise features are also evaluated experimentally in anechoic wind tunnel tests, and test data are used to validate the numerical simulations. The results show that the increase in descent speed leads to a reduction in the mean thrust. Significant thrust fluctuations are also observed when the rotor approaches the vortex ring state. Consequently, a substantial increase in sound pressure level in the low to medium frequency range is found in the far-field noise spectra, while the high-frequency sound pressure level shows a slight decrease. Furthermore, a noise source analysis is performed on the blade surface to help understand the corresponding noise mechanism.

Active control of cavity buffeting noise using a dielectric barrier discharge plasma actuator

This work examines the active control of vehicle buffeting noise using a dielectric barrier discharge plasma actuator (DBD-PA). First, the buffeting noise characteristics of a cavity under different inflow wind speeds are established through a wind tunnel test, and the effectiveness of the buffeting noise measurement results is verified. Various types of actuator layouts are designed based on specific combinations of parameters, and the interval optimization algorithm is used to identify the layout type of actuators that have the best equalization control effect under different inflow wind speeds. The experimental results regarding buffeting noise characteristics show that the buffeting frequency and the peak value of the sound pressure level increase with the increasing of wind speed. The control results show that the overall control effect of the reverse layout of the span-wise DBD-PA (SDBD-PA) is better than that of the positive layout. Consequently, the control effects of the SDBD-PA layout decrease in the front, rear, and oblique directions. A DBD vortex generator (DBD-VG) has no control effect when it is arranged in the front but has a certain control effect when it is arranged in the rear. The control effect is better with longer DBD-VGs. The results of running the interval optimization algorithm at different incoming wind speeds are as follows: reverse-front-SDBD-PA and long-rear-DBD-VG can achieve the best equalization control effect of cavity buffeting noise. The average noise reduction values are 5.26 dB and 4.42 dB, respectively, and the maximum noise reduction values are 7.48 dB and 5.79 dB, respectively.

Passive earplug including Helmholtz resonators arranged in series to achieve broadband near zero occlusion effect at low frequencies.

The use of passive earplugs is often associated with the occlusion effect: a phenomenon described as the increased auditory perception of one's own physiological noise at low frequencies. As a notable acoustic discomfort, the occlusion effect penalizes the use and the efficiency of earplugs. This phenomenon is objectively characterized by the increase in sound pressure level in the occluded ear canal compared to the open ear canal. Taking inspiration from acoustic metamaterials, a new design of a three-dimensional printed "meta-earplug," made of four Helmholtz resonators arranged in series, is proposed for achieving near zero objective occlusion effect measured on artificial ear in a broadband frequency range (300 Hz to 1 kHz). For this purpose, the geometry of the meta-earplug is optimized to achieve a null occlusion effect target based on an analytical model of the phenomenon. It results from the optimization process that the input impedance of the meta-earplug medial surface approximately matches the input impedance of the open ear canal, weighted by the ratio of volume velocity imposed by the ear canal wall to the ear canal cavity between open and occluded cases. Acoustic properties of the meta-earplug are also shown to significantly improve its sound attenuation at the piston-like mode of the system.

Numerical Study on Flow and Noise Characteristics of High-Temperature and High-Pressure Steam Ejector

Based on the shear stress transfer (SST) k-ω model, Ffowcs-Williams and Hawkings (FW–H) equation, and Lilley sound source equation, the flow and sound field of high-temperature and high-pressure steam ejectors are simulated. The entrainment performance, near-field sound source, and far-field noise of the steam ejector are discussed. The influences of working parameters including the primary steam pressure, the secondary steam pressure, and the back pressure are analyzed. The results show that under the design conditions, the steam ejector has two shock waves and three sound source regions. A shear layer at the boundary of the first shock wave generates the Sound source-I, and the flow separation at the boundary of the second shock wave causes the Sound source-III. The Sound source-II is located near the mixing chamber wall and the sound pressure levels around the ejector depend on the distances from the Sound source-II. In terms of the entrainment performance, with the increasing primary pressure or the decreasing secondary pressure, as the driving pressure difference of the secondary steam decreases, so does the entrainment ratio. As the back pressure increases, the entrainment ratio firstly remains constant, and then rapidly decreases when the back pressure exceeds the critical value at pb = 5.5 MPa. In terms of the noise characteristics, the sound pressure level and the intensity of the second shock wave have a positive correlation. When the primary or secondary pressure increases, the sound pressure level increases. Moreover, with the increasing back pressure, the sound pressure level firstly decreases, reaches the minimum of 98.2 dB at the critical back pressure, and then slowly increases.

Influence of frequency and intensity of bilateral audible sound waves on heat transfer performance of air-to-air heat exchange systems

To enhance the air heat transfer performance, this study applied the bilateral audible sound waves to an air-to-air heat exchanger. The effect of the frequency and intensity of sound waves on heat transfer performance was investigated from the viewpoint of flow instability and heat flux, and the sound power efficiency was also explored to reveal the efficiency of sound waves on the heat transfer performance. The results showed that the flow instability intensified with the increase in sound pressure level (SPL) and decrease in frequency, which was reflected by the distribution of turbulence kinetic energy. The change in sound waves has different effects on the turbulence kinetic energy at different locations, and the directivity distribution characteristics of the turbulence kinetic energy inside and outside the heat tube caused similar directivity distribution characteristics of the heat flux, in which the maximum value of the heat flux was located perpendicular to the flow direction. Additionally, the heat flux at different locations increased with an increase in SPL and a decrease in frequency. The heat transfer performance was relatively superior when the SPL was higher than 120 dB and the frequency was lower than 100 Hz, and a decrease in frequency could increase the sound power efficiency. This study can guide the application of sound waves in the heat transfer enhancement of air-to-air heat exchange systems.

Aerodynamic and Manovacuometric Vocal Measurements in Pregnant Women in the Second and Third Trimesters of Pregnancy

To describe and to correlate the aerodynamic and manovacuometric voice measurements of pregnant women. The following evaluations were carried out on 49 pregnant women - between 18 and 40 years old - in the second and third trimesters of gestational age: respiratory muscle strength, maximum phonation time of /a/, habitual, minimum, and maximum sound pressure levels. The data were statistically described and tested for the hypothesis of no association between voice measurements and refence levels, and for the correlation between voice measurements. The maximum phonation time of /a/, and the maximum inspiratory and expiratory pressures were significantly lower than expected. The habitual, minimum and maximum sound pressure levels were significantly higher than expected. The maximum sound pressure level showed a weak positive correlation with the maximum phonation time of /a/. There were moderate positive correlations between: minimum/maximum sound pressure level and habitual sound pressure level; maximum sound pressure level and minimum sound pressure level; and maximum expiratory pressure and maximum sound pressure level. A strong positive correlation occurred between maximum expiratory pressure and maximum inspiratory pressure. The pregnant women showed a decreased maximum phonation time of /a/, decreased respiratory pressures, and increased sound pressure levels. This suggests that pregnancy affects the respiratory dynamics regarding support of phonation and respiratory strength, which may generate a possible vocal abuse with the increase in sound pressure levels without respiratory support.

Noise and Critical Sound Levels During Non-Invasive Ventilation of a Preterm Infant in the Incubator.

Preterm birth and the subsequent necessary treatment in neonatal intensive care units (NICU) subjects the preterm infant to non-physiological noise exposure with potentially adverse consequences for short- and long-term development. Adjusters to improve the acoustic environment for the preterm infant need to be defined. Sound pressure level measurements during routine procedures in a NICU were performed by ¼" microphones placed inside and outside the incubator. The microphones need to be suitably positioned to measure sound pressure levels that are representative for the sound field inside and outside the incubator. The sound pressure level spectra generated by respiratory support and corresponding monitor alarms were compared. Inside the incubator, higher sound level pressures (in dBA) were generated primarily by the use of the system components of the incubator itself than outside, whereas when the incubator was closed, it had an insulating effect on sounds generated in the NICU. Non-invasive ventilation resulted in an increase in sound pressure levels from 50 to 60 dBA in the neonate's environment, with sound pressure levels increasing particularly in the frequency range above 1 kHz. Preterm infants are exposed to high sound levels, especially in the non-physiological high-frequency range, particularly during non-invasive ventilation. The continuous sound exposure could be further reduced to some extent by an optimized design of the incubator.

Combined effect of acoustic field and gas absorption on evaporation of slurry droplet

In this study, we developed a model of convective heat and mass transfer of an acoustically levitated slurry droplet that evaporates in an atmosphere of air, water vapor, and soluble gas. The advanced model considered the effects of acoustic streaming, forced convection, and non-isothermal gas absorption on the evaporation rate of a liquid droplet containing small solid particles. It is shown that the time of porous shell formation decreases with the increase of sound pressure level (SPL) and increases with the increase in frequency. Adding soluble gas to the gaseous phase shortens the time required for porous shell formation during slurry droplet drying. As shown by numerical calculations, in a gas mixture containing air with an ammonia content of 30%, at a temperature of 293 K and a humidity of 50%, with an acoustic field frequency of 2π·45 kHz and an SPL of 140 dB, the time of porous shell formation of a silica-water slurry droplet with the initial radius of 250 µm is about half shorter than that in a gas mixture not containing an active gas. The prediction of the developed model was in good agreement with the experimental results available in literature.

Aerosol emissions from wind instruments: effects of performer age, sex, sound pressure level, and bell covers

Aerosol emissions from wind instruments are a suspected route of transmission for airborne infectious diseases, such as SARS-CoV-2. We evaluated aerosol number emissions (from 0.25 to 35.15 μm) from 81 volunteer performers of both sexes and varied age (12 to 63 years) while playing wind instruments (bassoon, clarinet, flute, French horn, oboe, piccolo, saxophone, trombone, trumpet, and tuba) or singing. Measured emissions spanned more than two orders of magnitude, ranging in rate from < 8 to 1,815 particles s−1, with brass instruments, on average, producing 191% (95% CI 81–367%) more aerosol than woodwinds. Being male was associated with a 70% increase in emissions (vs. female; 95% CI 9–166%). Each 1 dBA increase in sound pressure level was associated with a 28% increase (95% CI 10–40%) in emissions from brass instruments; sound pressure level was not associated with woodwind emissions. Age was not a significant predictor of emissions. The use of bell covers reduced aerosol emissions from three brass instruments tested (trombone, tuba, and trumpet), with average reductions ranging from 53 to 73%, but not for the two woodwind instruments tested (oboe and clarinet). Results from this work can facilitate infectious disease risk management for the performing arts.

Evaluating the Influence of Targeted Air Flow on Sound Pressure Level and Closed Quotient

Purpose Measures of estimated subglottal air pressure and translaryngeal air flow enable the researcher or clinician to noninvasively assess aerodynamic features related to respiratory and phonatory function. Our goal was to examine the unique relationship between air flow with sound pressure level (SPL) during syllable production while attempting to hold fundamental frequency and subglottal air pressure relatively constant. Method We completed two studies. Study 1: During syllable production, resultant sound pressure level was measured under conditions of constant fundamental frequency and estimated subglottal air pressure while systematically varying translaryngeal air flow. Study 2: During syllable production, resultant sound pressure level and closed quotient (using laryngeal stroboscopy) were measured under conditions of constant fundamental frequency and estimated subglottal air pressure while systematically varying translaryngeal air flow. Results Study 1: Findings suggest a steady increase in sound pressure level with increases in air flow between 25 cc/s and 150 cc/s. Interestingly, relatively stable mean sound pressure level was maintained over a considerable range of air flow values between 225 and 450 cc/s, suggesting that air flow could be further increased without a marked loss of sound pressure level. Study 2: Findings suggest a systematic increase in mean sound pressure level as supraglottic activity subsided and as the closed quotient decreased from 0.80 to 0.58. Interestingly, sound pressure level was relatively stable as the closed quotient decreased from 0.58 to 0.35. Conclusions Our findings suggest that sound pressure level can be maintained over a considerable range of increasing translaryngeal air flow values and over a considerable range of decreasing closed quotient values. These results provide motivation for investigating the interaction between air flow, glottal closure, and sound pressure level among other measures of phonatory function, with important clinical implications for therapeutic approaches that emphasize increases in air flow and focus on reducing contact between the vocal folds.

The Feasibility of Gastroesophageal Manometry for Continuously Evaluating the Degree of Expiratory Effort During Successful Crescendo Phonation

This study aimed to assess the feasibility of gastroesophageal manometry for continuously evaluating the degree of expiratory effort by measuring the pressures in the digestive tract during crescendo phonation. Each of 18 healthy nondysphonic speakers had a probe with a four-channel gastroesophageal manometer inserted through the nasal cavity to place four pressure sensors in the hypopharynx, cervical-/thoracic esophagus, and stomach, and was asked to gradually increase the vocal loudness during sustained phonation of the vowel /e:/ (vowel-crescendo task), while the sound pressure level and the pressures were simultaneously recorded. 50% of the successful vowel-crescendo task samples with a gradual and adequate sound pressure level increase showed a concomitant gradual increase in both the intra-thoracic-esophageal/intra-gastric pressure values from approximately -5 mmHg /6 mmHg to -10 mmHg/20 mmHg, respectively. The maximum pressure value was the highest in the intra-gastric pressure followed by the intra-thoracic-esophageal and intra-cervical-esophageal pressures in order. However, most of the samples showed less than one of atypical pressure changes, such as fluctuations in the intra-thoracic-esophageal and intra-gastric pressure changes and dispersion in the intra-cervical-esophageal and intra-hypopharyngeal pressure values (perhaps due to the peristaltic motions, and the contact of the sensors to the membranous wall). These results show that, during successful crescendo phonation, gastroesophageal manometry reveals a gradual increase in the intra-thoracic and intra-abdominal pressures with increasing the vocal intensity, even though showing some systematic errors, suggesting the usefulness of gastroesophageal manometry for continuously evaluating the degree of expiratory effort without influence by the laryngeal condition.

The Influence of Load on the Vibration and Noise Characteristics of Transformer

In order to further understand and grasp the impact of load on the vibration and noise characteristics of the transformer, this article analyzes the impact of load factors, power factor, harmonic current, three-phase unbalance and other load factors on transformer vibration and noise from the perspective of transformer vibration mechanism. A 10kV/200kVA three-phase oil-immersed distribution transformer was used as the object. Experiments were conducted to study the changes in the spectrum distribution, noise intensity and A-weighted sound pressure level of the transformer vibration and noise under the influence of different load factors. The results show that: when the frequency increases, the amplitude of the 100Hz fundamental frequency in the vibration noise signal increases, and the noise level increases accordingly; when the power factor increases, the amplitude of the odd frequency components in the vibration noise signal gradually decreases with the increase of the power factor. There is no obvious fluctuation in amplitude except 100Hz. When the harmonic current and the three-phase are unbalanced, the spectral components become complicated and accompanied by a large number of odd-order frequency multiplication components. With the increase of harmonic content, the amplitude of vibration noise signal and A-weighted sound pressure level increase significantly; the degree of unbalance and the occurrence of unbalance have a greater impact on the amplitude of vibration noise signal and A-weighted sound pressure level. The research in this paper provides a reference for the noise suppression of power equipment and the fault diagnosis technology based on vibration and noise signals.

Evaluation of occupational noise exposure and general health of workers in industrial sites: A case study.

Occupational noise exposure in workplaces is the most common detrimental factor that has the greatest impact on the health of people working there. The aim of this study was to evaluate occupational noise exposure and its relation to the general health status in industrial workers in Sanandaj, Iran. This cross-sectional study was conducted on the general health of 500 male workers in Sanandaj using the General Health Questionnaire (GHQ-28). Likewise, occupational noise exposure was measured based on sound pressure level (SPL) and dosimetry in the work and rest conditions of workers. The results showed poor general health status of workers, exceeded the daily working hours and also the standard range of sound. A significant correlation was found between general health and its dimensions with indicators of workplace sound pressure levels (P < 0.05). This means that with the increase in sound pressure level is worse general health status. It seems that the health of workers in these industries is an inappropriate process due to exposure to occupational noise exposure and poor conditions of the workplace. A high percentage of them will lose their health in case of non-implementation of prevention programs and health in the workplace in the future.

A computational investigation of airfoil aeroacoustics for structural health monitoring of wind turbine blades

AbstractA generalized computational methodology for reduced order acoustic‐structural coupled modeling of the aeroacoustics of a wind turbine blade is presented. This methodology is used to investigate the acoustic pressure distribution in and around airfoils to guide the development of a passive damage detection approach for structural health monitoring of wind turbine blades for the first time. The output of a k − ε turbulence model computational fluid dynamics simulation is used to calculate simple acoustic sources on the basis of model tuning with published experimental data. The methodology is then applied to a computational case study of a 0.3048‐m chord NACA 0012 airfoil with two internal cavities, each with a microphone placed along the shear web. Five damage locations and four damage sizes are studied and compared with the healthy baseline case for three strategically selected acoustic frequencies: 1, 5, and 10 kHz. In 22 of the 36 cases in which the front cavity is damaged, the front cavity microphone measures an increase in sound pressure level (SPL) above 3 dB, while rear cavity damage only results in six out of 24 cases with a 3‐dB increase in the rear cavity. The 1‐ and 5‐kHz cases show a more consistent increase in SPL than the 10‐kHz case, illustrating the spectral dependency of the model. The case study shows how passive acoustic detection could be used to identify blade damage, while providing a template for application of the methodology to investigate the feasibility of passive detection for any specific turbine blade.

Soundscape Assessment of Aircraft Height and Size.

It is accepted knowledge that, for a given equivalent sound pressure level, sounds produced by planes are worse received from local communities than other sources related to transportation. Very little is known on the reasons for this special status, including any interactions that non-acoustical factors may have in listener assessments. Here we focus on one of such factors, the multisensory aspect of aircraft events. We propose a method to assess the visual impact of perceived aircraft height and size, beyond the objective increase in sound pressure level for a plane flying lower than another. We utilize a soundscape approach, based on acoustical indicators (dBs, LA, max, background sound pressure level) and social surveys: a combination of postal questionnaires (related to long-term exposure) and field interviews (related to the contextual perception), complementing well-established questions with others designed to capture new multisensory relationships. For the first time, we report how the perceived visual height of airplanes can be established using a combination of visual size, airplane size, reading distance, and airplane distance. Visual and acoustic assessments are complemented and contextualized by additional questions probing the subjective, objective, and descriptive assessments made by observers as well as how changes in airplane height over time may have influenced these perceptions. The flexibility of the proposed method allows a comparison of how participant reporting can vary across live viewing and memory recall conditions, allowing an examination of listeners' acoustic memory and expectations. The compresence of different assessment methods allows a comparison between the “objective” and the “perceptual” sphere and helps underscore the multisensory nature of observers' perceptual and emotive evaluations. In this study, we discuss pro and cons of our method, as assessed during a community survey conducted in the summer 2017 around Gatwick airport, and compare the different assessments of the community perception.

Investigation of Tooth Precision on Meshing Noise of Planetary Gear Train

Noise is one of major serious issues for planetary gear trains (PGTs). It is called noise hazard in serious cases such as cabin in a helicopter where the sound level reaches 100dB. In this paper, several precisions of planet gears are combined to investigate the influence of tooth precision on meshing noise of PGTs. The meshing noise of PGTs is generated by stiffness coefficient excitation and error excitation forces, but stiffness coefficient excitation is assume to be constant in this paper because slight error on the tooth surface doesn't effect on meshing stiffness. It was found that maintaining the same precision for all planet gears is the best; if one of the planet gears has a precision far from the others, the sound pressure level increases. The deviation for the maximum error among all meshing pairs, should be restricted to no more than 3μm in case of module one spur gear.

Microvane in controlling noise in open cavity flow

The cavity can be commonly found in aircraft and they are used to store weapons, cargo and also landing gear. Despite the importance of cavity, they can cause vibrations and noise that can disturb the aircraft performance. In order to overcome these problems, the microvane had been studied in controlling noise on open cavity flow. The investigation was carried out at a flow speed of 64.97 meters per second with Reynolds number of 4.3 × 106 per meter on cavity with length over depth ratio of 5. The study tested two configurations of microvane which are counter-rotating and co-rotating orientation. The results show that counter-rotating microvane performed better than co-rotating microvane to suppress cavity noise. The use of counter-rotating microvane managed to reduce the sound pressure level throughout the cavity by 3 % with the highest reduction of 24 decibels. However, the co-rotating microvane cause overall increase of sound pressure level by 0.3 % with the highest reduction of 7 decibels.

Drivers’ physiological response and emotional evaluation in the noisy environment of the control cabin of a shield tunneling machine

Being a driver in the control cabin of a shield tunneling machine is a high-pressure career. The physiological responses and mood swings of a driver are vital to his occupational health and construction safety; however, a driver’s emotional intensity and physiological reactions in a noisy environment have not been considered. This study aims to investigate how a driver’s emotional intensity and physiological responses in a noisy environment can be altered. On-site measurements were conducted in an urban metro system, and an emotional survey was performed. A wearable device was used as a physiological measurement tool to obtain heart rate data from a driver. Results indicate that the driver pays considerable attention to the noisy environment. The sound pressure level in the control cabin was in the range of 96.8–98.7 dBA. The driver’s emotion is influenced when the sound pressure level increases to 94.5 dBA. The relationship was significant between the emotional intensity and the sound pressure level. The fear was highly evident with the sound pressure level increase given that the drivers were concerned about operational errors. The heart rate of the driver was significantly influenced in the noisy environment for a long time. The increased heart rate at 92–96 dBA was faster than at other ranges of sound pressure level. The emotional intensity had impacts on the heart rate of the driver. The disliking influenced the heart rate more obviously than the other two emotional types. The driver’s emotion has a relationship with social background.