Sound Pressure Level Research Articles

Numerical study of shell-side flow-induced noise characteristics of staggered straight tube bundle heat exchanger under different inflow conditions

This paper presents a numerical study on the shell-side flow noise characteristics of staggered straight tube bundle heat exchangers under varying inflow conditions. A three-dimensional numerical model of a compactly arranged staggered straight tube bundle heat exchanger was established. To validate the numerical model, a feasibility study using a cylindrical flow model was conducted. Subsequently, the large eddy simulation (LES) method was employed to investigate the unsteady shell-side flow field characteristics, and the vortex characteristics of the flow field were obtained based on the Q-criterion. Finally, the acoustic finite element method (FEM) was utilized to calculate and analyze the noise characteristics at the inlet and outlet positions of the heat exchanger shell side. The results show that the inflow angle has an influence on both the flow field and the acoustic field of the heat exchanger shell side. As the inflow angle increases, the flow stability decreases, horseshoe vortices replace boundary layer vortices, and the decrease in fluctuating pressure leads to a reduction in flow noise. Analysis of the sound pressure level spectrum indicates a line spectral characteristic at low frequencies, with high-frequency components experiencing rapid attenuation.

Harmonic acoustic pneumatic source (HAPS) to generate sound at very low-frequency

At very low frequency, the loudspeakers face technical issues (size, weight, energy consumption). An alternative to the electrodynamic loudspeaker is the Harmonic Acoustic Pneumatic Source (HAPS) demonstrated efficient in active tonal control. It comprises a high-pressure pneumatic air source, a rotating flow chopper, and an exhaust. The rotation of the flow chopper generates a pulsed flow which radiated noise out from the exhaust. An analytical model of the HAPS is presented to introduce the main challenge associated with its use at very low frequencies: having a high mean flow rate with a relatively small exhaust duct section. To overcome these challenge, a dedicated flexible tube (under light mean pressure) is added to the exhaust circuit to obtain a pulsating sphere activated by a HAPS. This configuration has been experimentally studied in a semi-anechoic room with two flexible tubes and without. The sound pressure level of the first harmonic at 1 meter range from 75 to 95 dB SPL (25 to 160 Hz, plenum pressure from 5 to 20 PSI). Thanks to fluid-structure interaction, the fundamental harmonic sound levels radiated by the compliant tube were free of jet noise. The drawback is the high harmonic distortion observed during the experiments.

A time-domain approach to predict sound radiation from track vibrations

With the intended shift of transport from road to railway, noise exposure due to railway noise will increase. Auralisation of the noise is a key tool for assessing noise perception beyond equivalent sound pressure levels. Researching the connection between, for example, track design parameters and perceived sound quality holds potential for perception-centered track design. A computationally efficient model is required to render the sound field generated by the track vibration. In this paper, using simulated time-domain surface velocities of a rail and sleepers as input, such a model is presented. The sound pressure signal in a position on the side of the track is efficiently predicted by convolving these velocities with precalculated acoustic transfer functions. For a typical ballasted track, the necessary spatial discretisation of the evaluated velocities is determined in a convergence study. Further, the required length of the finite section of the track to be included in the prediction is specified. Finally, pass-by signals generated by track vibration are demonstrated.

Sounding São Paulo: exploring the acoustic environment of Vai-Vai Samba School

In the study, a broader approach to urban planning was explored, surpassing traditional noise analyses that often neglect subjective aspects. The focus centered on the soundscape of the Vai-Vai Samba School, a cultural landmark in São Paulo's Bixiga neighborhood, renowned for its Afro-Brazilian heritage since its establishment in 1930. Following ISO 12913 guidelines, measurements of sound pressure level, binaural analyses for psychoacoustic parameters, and interviews with attendees were conducted to comprehend sound sources, perceived quality, and perceptions of the surrounding sound environment. By correlating quantitative and qualitative data, the interaction between objective and subjective analyses was examined. This study offers valuable insights for urban planning, underlining the significance of considering history and culture when addressing soundscape matters.

Psychoacoustic characteristics of music soundtracks moderate juice taste perception

Eating and drinking constitute the most multisensory aspect of our daily lives. Altering external sensory factors, particularly auditory stimuli, has been suggested as a promising factor for influencing taste perception. In this context, this study investigated the effect of music on the taste of orange juice in a multisensory and controlled indoor environment laboratory (Sens i-Lab). We conducted a juice-tasting experiment, focusing on individuals' flavour perception while exposed to eight music soundtracks that were created, manipulating three sonic attributes (Articulation, Tempo and Pitch). The audio stimuli underwent analysis using various psychoacoustic parameters, including sound pressure level, loudness, sharpness, roughness, fluctuation, and tonality. Correlation analysis revealed specific patterns between the average taste ratings of orange juice and the psychometric characteristics of eight music soundtracks. The sweet flavour exhibited negative correlations with roughness. Besides, the sour and bitter taste showed positive correlations with sound level.

Revision of Sabine's and Eyring's reverberation theories

Sabine's and Eyring's reverberation theories are still the most important theoretical frameworks for room acoustics. The important physical quantities derived from these theories are the average sound pressure level (sound energy density) and the reverberation time (sound energy decay). Eyring revised Sabine's theory to become the reverberation time zero in the perfect absorption condition. However, Eyring's theory has contradictions regarding the sound energy density in a steady state and the energy decay from the steady state. In this study, in order to resolve these contradictions, the theoretical framework for the consistent system is presented introducing the new concept of the average impulse response in a room, and the contradictions in the current room acoustic theory are clarified. Based on the theoretical framework, Sabine's reverberation theory is revised by a different way of Eyring's theory. The reverberation time of the revised theory is shorter than that of Sabine's theory and longer than that of Eyring's theory. Finally, ray-tracing computer simulations were performed to verify the revised theory. Results of sound ray tracing simulations were in better agreement with the values calculated using the revised theory rather than those calculated using Sabine's and Eyring's theories.

Basic examinations of the sound transmission loss measurement using two cardioid microphones

This paper reports results of an experiment on sound transmission loss measurement using the C-C method. This method is an inexpensive and stable method for measuring the sound pressure, the particle velocity, and the sound intensity. The measurements are carried out in accordance with JIS A 1441-1:2007 based on ISO 15186-1:2000, and the C-C method is applied for measuring the sound intensity. Comparing the measured results with those of the sound pressure level difference method, comparable results are obtained above 250 Hz. Naturally, the precision of the measurements depends on the microphone calibration used in the C-C method. In this report, we employ two calibration methods using an acoustic tube and an anechoic chamber, and also exhibit comparison of the results obtained by these methods.

Railway psychoacoustic annoyance - an indicator for planning infrastructure projects

The joint project "Real-time Calculation, Auralization and Visualization of Sound Propagation and Noise Protection Measures for Infrastructure Projects" (EAV-Infra), funded by the German Federal Ministry for Economic Affairs, investigates the potentials of digital infrastructure planning based on Building Information Modeling (BIM) in combination with state-of-the art Auralization and Visualization technology as well as Psychoacoustic Modelling. Currently, log-scaled sound pressure levels, which are only informative to experts, are used to communicate the topic of noise exposure to the public. Auralization, in combination with a hearing-oriented noise index, will constitute a more intuitive and understandable evaluation basis for residents. One focal point of EAV-Infra is the development of a linearly-scaled metric for railway noise, which correlates better with human perception than the LAeq. Binaural recordings of a wide spectrum of different railway pass-by scenarios were presented in listening experiments to obtain semantic-differential information about the sounds as well as global and continuous annoyance ratings for individual passings. Currently, a railway psychoacoustic annoyance metric is being developed by comparing two fitting methods: a classical model based on common psychoacoustic quantities, as well as an AI model with a Mel-log-spectrogram-CRNN architecture. The approach and first results will be discussed in this contribution.

How to deal with unsuspected source of annoyance in electric vehicle cabin using the "sonic augmented" concept?

The disappearance of the main source of noise with electric vehicles resulted in a breakthrough in car cabin sound experience. Despite significantly lowering the sound level pressure, one cannot claim perfect quietness is achieved. Indeed, as the auditory masking produced by the internal combustion engine is not effective anymore, unsuspected sounds such as electric whistling, whining or switching are now part of this sound environment and may be identified as unpleasant sounds. However, drivers' expectations are to have audible feedback indicative of vehicle operation that matches their expectations. Therefore, the presence of unwanted and unpleasant sounds, on the one hand, and the absence of desired and informative sounds, on the other hand, is an opportunity for sound design to create a new sound environment inside car cabins. The present work proposes a "sonic augmented" concept based on the idea of adding designed sounds, called "masks", participating both in the overall soundscape augmentation and in the attenuation of unpleasant sounds, called "defects". Sound design strategies with different parametrizations will be presented, as well as the results of two perceptive experiments whit the aims at evaluating the impact on perceptive attenuation of "defects" and the overall sound quality.

Iterative eigenvalue method coupled with RSM for structural acoustic analysis and optimization of the CLD-damped orthotropic steel deck

In the present work, an iterative eigenvalue method (IEM) is proposed and combined with the boundary element method (BEM) to perform the structural acoustical analysis of the orthotropic steel deck (OSD) damped with constrained layer damping (CLD), through which the frequency-dependent properties of the viscoelastic core can be accurately considered. Then, a series of hammer tests are carried out in a semi-anechoic chamber to verify the acoustic prediction method. It shows that the simulated structural noises basically agree with the test results, and the overall deviations at the field points M2 and M8 are merely 2.4 and 2.3 dB, respectively. Subsequently, taking the thicknesses of the damping layer and the constraining layer, as well as the material properties of the constraining layer as design variables, a central composite experiment is designed and combined with response surface methodology (RSM) to fit the relationship between analysis objectives and design variables. With the objective of minimizing the acoustic radiation power, a program for finding the optimal values of design variables is developed based on the interior penalty function method. Through iterative computations, the optimal points are numerically determined as t 1 = 2.3 mm and t 2 = 0.3 mm for the thicknesses of the damping layer and the constraining layer, respectively. Steel alloy is found to be the optimal material for the constraining layer. After optimizing CLD treatment, the overall acoustical power level can be reduced from 97.7 dB to 93.1 dB and the overall sound pressure levels (SPLs) at the field points M2 and M8 can be reduced from 89.2 dB to 83.5 and 76.9 dB to 70.3 dB, respectively, indicating that the optimization of CLD design parameters can significantly improve acoustic performance of the CLD-damped structures.

Systematic review of environmental noise in neonatal intensive care units.

To systematically review the literature on noise exposure within the neonatal intensive care unit/special care nursery settings, specifically to describe: noise characteristics, sources of noise and ways of measuring noise. Systematic searches were conducted through databases Medline, Embase and PubMed. Studies were included if they met the inclusion criteria (1) reported noise characteristics; (2) reported noise exposure measurements; (3) in the neonatal intensive care unit/ special care nursery settings. Methods and key findings were extracted from included studies. Quality analysis was done using a modified version of the Newcastle-Ottawa Scale. We identified 1651 studies, screened 871, reviewed 112 and included 47. All reported NICU average equivalent sound levels were consistently louder than recommended guidelines (45 dB). The most consistent association with higher sound pressure levels were noise sources grouped under people congregation. Half of the studies did not use measuring devices adhering to international sound level meter (SLM) standards. All NICUs exceeded recommended accumulative sound levels. People were the most consistent source of noise. Sound pressure levels need to be consistently measured with devices adhering to international SLM standards in future studies.

Effects of sound on bluff body aerodynamic characteristics in separated and reattaching flows

The coupling effects between sound and flow on the aerodynamic characteristics of bluff bodies are commonly encountered in engineering practices, such as wind turbine blades and heat exchanger compressors. This study experimentally investigates the effects of sound over a broad range of frequencies (0–400 Hz) and sound pressure levels (80–105 dB) on the streamwise wind pressures on a flat plate in both smooth and turbulent flows. Spectral analysis and proper orthogonal decomposition (POD) are employed to explore the effects of sound on the aerodynamic forces acting on the flat plate. The results show that the effects of sound on wind pressure distributions and separation bubble behaviors over the flat plate depend on both sound frequency and sound pressure level. Furthermore, the findings highlight the role of acoustic resonance, which can increase the fluctuating wind pressure on the plate surface by over 400%. These effects can also be influenced by sound pressure levels. Additionally, the results demonstrate varying degrees and forms of attenuation of sound effects in turbulent flows, depending on the wind flow characteristics.

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.

Acoustic comfort in primary- and nursery-school canteens: From measurements to recommendations

Canteens usually have critical acoustic conditions resulting from the need to maximize the number of occupants while minimizing volume. Thus, in the absence of specific sound absorbing treatments, very high sound pressure levels are usually observed resulting in significant impairment of communication (with increased vocal effort of speakers and reduced speech intelligibility), and dangerously high exposure levels for workers. The present paper reports acoustic measurements carried out in a nursery school canteen having a volume of 212 m3 and seating about 50 children, and two primary school canteens having volumes of 656 m3 (seating 150 children) and 367 m3 (seating 107 children). Reverberation time was measured in each room as well as sound pressure levels during peak occupation (averaged over 15-minute intervals), resulting in A-weighted sound pressure levels spanning between 81 dB (in the nursery school) and 90 dB in the primary schools. Starting from the observed values, considerations about the group-size of the occupants as a function of age were made, and recommendations were finally given to guide the acoustic correction of similar spaces.

Revisiting the sound absorption mechanisms of a finite flexible perforated panel absorber using a numerical approach.

This study investigates the sound absorption mechanisms of a finite flexible perforated panel absorber. Different from existing work where the mechanisms were often investigated by comparing the sound absorption coefficient curves of different absorber configurations, a numerical approach, called virtual impedance tube (VIT) technique, is developed and used for the analysis. One advantage of this technique is the vast dataset generated can be used to investigate the sound absorption mechanisms from an energy standpoint. The developed VIT technique is first validated using the impedance tube test, where a proportion-integration-differentiation control algorithm is developed to maintain the incident sound at a desired sound pressure level. Then, the sound absorption mechanisms at three absorption peaks, i.e., hole-cavity controlled, panel-cavity controlled, and panel controlled, are investigated and the dominant energy dissipation mechanism at different sound pressure levels (SPLs) is revealed. Finally, an impedance model that takes account of the panel vibration and is applicable to various SPLs is proposed and validated.

Porous acoustic metamaterial for simultaneous control of high and low frequency machinery noise: Case study of a water pump.

An acoustic metamaterial (AMM) consisting of a porous material (melamine foam) layer above a symmetrical labyrinthine metamaterial, incorporating a micro-hole and micro-slit cover plate, is proposed to simultaneously mitigate low and high frequency noise from industrial machineries. Theoretical model of sound absorption by this AMM is developed and validated numerically and experimentally. Sensitivity analysis indicates that increasing the length of the labyrinthine pathway and cover plate thickness and decreasing the slit width, slit length, and hole diameter shifts the peak sound absorption to lower frequencies. This material is successfully applied as a sound absorptive enclosure of a 0.5 hp water pump to reduce its sound pressure levels across widely separated frequencies of 1414-2245 Hz (high frequency) and 176-222 Hz (low frequency). This study offers guidelines to noise control engineers for controlling low and high frequency noise in industrial machineries.

A novel dataset of indoor environmental conditions in work-from-home settings

During the last week of March 2020, millions of workers around the world transitioned to working from home due to the COVID-19 pandemic. While much research has explored the behavioural and psychological aspects of work-from-home (WFH), few studies have provided data-driven evaluations of indoor environmental quality (IEQ). This paper presents findings from a summer 2022 field study of IEQ conditions in WFH settings, involving 95 participants in the North American Pacific Northwest. Sensors installed on participants' work desks continuously measured total volatile organic compounds (tVOC), particulate matter (PM2.5), carbon dioxide (CO2) air temperature, humidity, and sound pressure levels (SPLs). Participants also completed surveys on home and workspace characteristics, as well as their subjective assessments of IEQ, well-being, and productivity. The study found that mean indoor concentrations of tVOC, PM2.5, and CO2 were 262 ppb, 5 µg/m3, and 712 ppm, respectively. Indoor air temperature ranged between 14.7–32.3°C, with a mean of 22.8°C, while relative humidity and SPL averaged at 52.5% and 53.7 dBA. Statistically-significant associations were observed between IEQ variables and factors such as residence type, cooking habits, workspace type, and window availability. A future paper will assess the surveyed behavioural and psychological characteristics in greater detail.

Research on flow-induced radiated noise of twin-screw pumps based on the Lighthill acoustic analogue theory

Abstract To optimize the control of twin-screw pumps (TSP), it is essential to ensure performance while simultaneously preventing noise levels from exceeding specified limits. In order to investigate the flow characteristics and the mechanism of flow-induced radiated noise under various operating conditions, a coupled numerical simulation approach using Computational Fluid Dynamics (CFD) and Computational Acoustics (CA) was employed, and the findings were validated through experiments. The study reveals that the highest sound pressure levels of radiated noise occur near the rotor outlet surface, and the dynamic-static interference at the rotor-boundary interface is the primary cause of flow-induced noise in TSP. The flow-induced noise in TSP exhibits dipole characteristics, with the overall sound pressure level gradually increasing and then sharply rising with the increase in rotational speed (or flow rate). It stabilizes near the design operating point and continues to increase steadily with further increases in rotational speed (or flow rate). Modal testing using a dual-distributed measurement technique highlights significant interference effects between the rotor inlet and the dynamic rotor for the first two Blade Passing Frequencies (BPF) in TSP. The results of this study provide a theoretical foundation for the low-vibration and low-noise design and operation of TSP.

Reflection function, reflectance, and area function measurements in ears of children and adults.

The main experiment concerned time-domain measurements of the acoustical reflection function (RF) of the human ear in adults and children (aged 5 to 8 years) using a probe inserted into the ear canal. This RF was used to calculate the area function of the ear canal versus distance along its centerline. Acoustical reflectance was calculated in the frequency domain from the RF, as was the difference in sound pressure level near the tympanic membrane relative to the probe tip. Group responses in area function, total ear-canal length, absorbance and group delay, and admittance magnitude and phase were analyzed based on sex, ear, and age. Responses were compared between children/adults and younger/older adults relative to age 50 years. Ear and sex were never significant. Significant differences were observed in children compared to adults in the area function, absorbance and group delay, and admittance magnitude and phase (0.25-4 kHz). Group delay differed between younger and older adults. A second experiment assessed level dependence of responses to better understand limitations in probe performance observed in the main experiment. These results show the utility of time-domain measurements of the area function and derived reflectance to understand sound-transmission differences across age at frequencies important to middle-ear function.

Effect of the magnitude of abrupt change in sound pressure on the magnitude and phase synchrony of 40-Hz auditory steady state response

A periodic sound with a fixed inter-stimulus interval elicits an auditory steady-state response (ASSR). An abrupt change in a continuous sound is known to affect the brain’s ongoing neural oscillatory activity, but the underlying mechanism has not been fully clarified. We investigated whether and how an abrupt change in sound intensity affects the ASSR. The control stimulus was a train of 1-ms clicks with a sound pressure level (SPL) of 70 dB at 40 Hz for 1000 ms. In addition to the control stimulus, we applied six stimuli with changes consisting of a 500-ms train at 70 dB followed by a 500-ms similar train with louder clicks of 75, 80, or 85 dB or weaker clicks of 55, 60, or 65 dB. We obtained the magnetoencephalographic responses from 15 healthy subjects while presenting the seven stimuli randomly. The two-dipole model obtained for the 40-Hz ASSR in the control condition was applied to all of the stimulus conditions for each subject, and then the time–frequency analysis was conducted. We observed that both the amplitude and the inter-trial phase coherence of the 40-Hz ASSR transiently decreased and returned to the steady state after the change onset, i.e., the desynchronization of 40-Hz ASSR. The degree of desynchronization depended on the magnitude of the change regardless of whether the sound intensity increased or decreased, which might be a novel neurophysiological index of cerebral response driven by a change in the sensory environment.