A-weighted Sound Pressure Level Research Articles

The influence of the reference level on loudness and preference judgements for spectrally manipulated fan sounds.

Fan sounds are often quantified using A-weighted sound pressure levels, silently acknowledging their limitations to fully capture the perceived unpleasantness. To overcome this limitation, level adjustments are a way to quantify the subjective preference of spectrally different sounds in listening experiments by adjusting the level of a test sound until it is equally preferred to a fixed reference sound. Since equal loudness contours differ, depending on the overall level, level adjustments might vary for different levels of the reference sound. This study aims to quantify the effects of spectral manipulations on level adjustments for loudness and preference judgements at reference sound pressure levels of either 45, 60, or 75 dB(A). Level adjustments of up to 12 dB were measured to make the stimuli equally preferred to the reference, particularly for sounds with prominent high-frequency components. The loudness and preference judgements were closely linked with each other, but an offset of about 3.5 dB at a reference level of 45 dB(A) indicates that equal loudness is not synonymous with equal preference. A linear regression model to predict level adjustments based on the reference level and an index reflecting the ratio of mid- to high-frequency loudness explains 73% of the variance.

Acute effects of military aircraft noise on sedative and analgesic drug administrations in psychiatric patients: A case-time series analysis

BackgroundExisting evidence suggests that psychiatric patients are highly noise sensitive, and that noise exposure increases the risk for adverse mental health outcomes, such as psychiatric hospitalizations and even suicide. To investigate acute effects of noise in this vulnerable population, we assessed short-term associations between fighter jet noise and on-demand sedative and analgesic drug administrations in a psychiatric clinic located close to a military airfield in Switzerland. MethodsWe applied a case time series analysis with an hourly time resolution using distributed-lag models. Analysis was adjusted for long-term and seasonal trends, day of week, time of day, time-varying weather conditions and the week of stay. Noise exposure (hourly A-weighted equivalent continuous sound pressure levels (LAeq)) was modelled using detailed flight plans and noise footprints for different fighter jet and route combinations. Outcome data were available from the clinic’s records. OutcomesDuring the study period (06/2016–12/2021), 23,486 flights occurred. 5,968 clinical stays with a median length of 41 days (IQR: 28d, 50d) were recorded. The odds ratio (OR) for medication administration over the lag period of 3 hours after exposure was 1.016 (95 %CI: 1.006, 1.026) per 10 dB LAeq for sedatives and 1.032 (95 %CI: 1.016, 1.048) per 10 dB for analgesics. Effects were larger in multimorbid patients. InterpretationCase time series analysis is a novel method to investigate transient associations in observational data while minimizing risk of bias. Using an objectively recorded outcome measure, our results demonstrate that psychiatric patients are a vulnerable population, in which noise exposure can lead to symptom exacerbations and adverse events.

Aerodynamic noise characteristics of a centrifugal fan in high-altitude environments.

In high-altitude areas, the air is thin and the atmospheric pressure is low, which can affect the performance of centrifugal fans and aerodynamic noise. In this paper, steady and unsteady simulations of a centrifugal fan flow field are performed at altitudes of 0, 1000, 2000, 3000, 4000, and 5000 m, and the Ffowcs Williams-Hawkings equation is used to predict the aerodynamic noise of the fan. The results indicate that the tonal and broadband noise generated by the fan decrease with increasing altitude, and the A-weighted sound pressure level of each frequency band of the fan decreases when the air volume is held fixed. The maximum sound power level Lwmax, sound pressure pulsation interval, and total noise sound pressure level Lp decrease linearly with increasing altitude. For every 1000 m increase in altitude, Lwmax and Lp decrease by 0.45 dB and 1.05 dB respectively. The fan noise characteristics, performance parameters, and human auditory perception are the main factors that affect the establishment of fan noise standards in high-altitude areas.

Annoyance penalty due to the spectrum shape of wideband noise

Environmental noise exposure is usually evaluated by measuring the A-weighted equivalent sound pressure level, LAeq [dB]. However, it cannot alone explain the resulting noise annoyance. It is common to apply penalties, such as +5 dB correction, to measured LAeq when the noise contains annoyance accentuating features, such as tonality or impulsiveness. Although previous studies suggest that the noise spectrum also influences annoyance, and spectrum is easy measure, the need of penalty due to spectral shape of noise has not been studied. Our study investigated the relationship between spectral shape and annoyance. The purpose was to determine whether spectrum-related penalties should be integrated with measured LAeq values. We conducted a psychoacoustic laboratory experiment involving 40 participants. We collected their annoyance ratings for 23 spectrally different steady-state wideband noises presented at three LAeq levels, 32, 40, and 48 dB. In addition, annoyance ratings were collected for a spectrally neutral reference noise played within 28–60 dB in 4 dB steps to enable the determination of penalty. The annoyance strongly depended on the spectrum of noise, for all three LAeq levels. Higher concentrations of sound energy in high frequencies were associated with increased annoyance ratings across all three LAeq levels. The penalty values of spectrally modified noises varied within −2 to +12 dB. The penalty values exhibited minimal dependence on LAeq. That is, the same spectrum-related penalties were valid at least within 32–48 dB. Our findings suggest that noise spectrum also deserves a penalty procedure to better explain human perception of noise.

Effect of embankment slope on road traffic noise propagation: numerical investigation and construction of correction formula for difference by slope angle

The propagation characteristics of road traffic noise from an embankment road are investigated through three-dimensional wave-based numerical analysis. Since this is a large-scale problem, we use the fast multipole boundary element method (FMBEM) as a highly efficient wave-based numerical method. We analyze sound fields around embankments with various slope angles and clarify that the sound pressure gradient changes with the slope angle, and in particular, the sound pressure level (SPL) distribution changes significantly near the line where the embankment slope meets the ground surface. When the prediction plane is an orthogonal cross-section to the direction of the lane, the distribution of the difference in A-weighted SPL between the case where the embankment is sloped and the case where it has a right angle is generally similar regardless of the position of the prediction plane. Based on this result, we propose an empirical formula to express the difference between the case with a slope and the case with a right angle. We confirm that the proposed formula provides a certain level of accuracy regardless of the location of the prediction plane when we appropriately determine the coefficients in the formula for each case from the viewpoint of error minimization.

Annoyance Prediction of Civil Aircraft Cabin Noise Based on Generalized Additive Models

Noise in civil aircraft cabin is a major contributor to passenger comfort. It is of great significance to predict the noise annoyance by developing a model. However, the low accuracy of linear model and the poor intelligibility of the neural network are the critical problems to be solved. Generalized additive models (GAMs) have become a leading choice for explainable machine learning. This study examines the effectiveness of GAMs in noise annoyance prediction. First, the annoyance of the cabin noise was collected through subjective listening test. Subsequently, three physical acoustic features (sound pressure level, A-weighted sound pressure level, preferred speech interference level) and five psychoacoustic features (loudness, sharpness, roughness, fluctuation strength, tonality) were applied to describe the stimuli. In the third step, three algorithms were used to construct GAMs based on annoyance (dependent variable) and feature parameters (independent variables), and the prediction accuracy was computed by ten-fold cross-validation. The result indicated that GAMs have higher prediction accuracy than linear regression model. The importance of features was evaluated, which is more intelligible than the neural network. This study provides the first assessment of GAMs in the annoyance prediction of civil aircraft cabin noise, and the findings may be of assistance to engineering noise control.

Study on compatibility of reduction transmitted impact sound of dry-type floating floor due to car-tire source and rubber ball source

In Japan, JIS A 1418-2:2019 specifies the car-tire with impact force characteristics (1) and the rubber ball with impact force characteristics (2) as standard heavy impact sources. It has also been reported that the reduction of transmitted impact sound for a dry-type floating floor differs depending on the impact sources of the car-tire and the rubber ball. It has been reported that one of the reasons for different reduction of transmitted impact sound is excessive the car-tire impact force, and a tendency for a nonlinear response to impact force for a dry-type floating floor. Meanwhile in inter.noise 2022, It was also suggested that the reduction of transmitted floor impact sound level of the rubber ball could be estimated from the reduction of transmitted floor impact sound level of the car-tire by considering excitation frequency characteristics. In this paper, a consideration was conducted using the impact force exposure level of the impact source as a method of correcting the excitation frequency characteristics. Also, the results on the comparison of reduction transmitted impact sound using the A-weighted sound pressure level are described.

A laboratory experiment on subjective evaluation of the sound quality of aircraft noise

This study investigates the relationship between aircraft noise's sound quality and subjective impressions. Laboratory experiments were conducted to examine how the impression of aircraft noise differs depending on its sound quality. First, an experiment by the semantic differential method was conducted using sounds of various aircraft models, including those from the 2000s and earlier, as stimuli. The results showed that even when the A-weighted sound pressure levels were equal, the sounds of recent aircraft were perceived more positively, suggesting that a decrease in sharpness was the cause. In addition, another experiment by the method of adjustment was conducted to examine the effect of extraordinary tonal sounds included in aircraft noises. As a result, it could not be said that the extraordinary tonal sounds negatively affected the evaluation of aircraft noise.

Subjective evaluation test on the effect of tonal components on broadband noise

Environmental noise sometimes contains tonal components, and it has been pointed out that this can be responsible for increasing the annoyance of noise. In Japan, noise problems related to tonal noises generated from wind turbines and heat pump systems have recently been occurring. To solve the noise problem, it is necessary to quantitatively understand the effect of tonal components on noise annoyance. In this study, annoyance evaluation experiments were conducted using broadband noise containing a tonal component. Four types of noise were used for the auditory test: white noise, pink noise, and low-frequency prominent noise that simulated indoor- and outdoor environmental noise. The frequencies of tonal components added to the broadband noise were from 50 to 2000 Hz, with intensities where the tonal audibility was 0, 5, 10, and 15 dB. The results show that the annoyance increases with the intensity of the tonal component, but the amount of increase depends on the frequency characteristics of the background noise and the tonal frequency. This increase in annoyance was quantified as a penalty in A-weighted sound pressure level.

Psychological and physiological evaluations of time-varying noises produced by air conditioners

Air conditioners are widely used in buildings to maintain thermal comfort for long time. Air conditioners produce sounds during operation, and air conditioners are regarded as one of the main noise sources in buildings. Most sounds produced by the air conditioner do not fluctuate over time and sound quality of the steady sounds produced by the air conditioner have been evaluated. However, air conditioners sometimes produce time-varying noises. Customers criticizes such noises are annoying when they sleep and they spend time quietly in the living room. The aim of this study was to determine the factors that significantly influence the psycho-physiological response to the time-varying noises produced by air conditioners. We assessed the A-weighted equivalent continuous sound pressure level (LAeq) and factors extracted from the autocorrelation function (ACF). Subjective loudness, sharpness, annoyance, and electroencephalography (EEG) were evaluated. Relationships between psychological and physiological responses and physical parameters, LAeq, the ACF factors, and their standard deviation, were determined. The LAeq and peak of the first maximum peak of the ACF were identified as significant factors for the time-varying noises.

A mini review of the Chinese literature on noise maps

According to the recently published 'Noise pollution prevention and control action plan' by the Chinese government, all the prefecture-level cities should achieve acoustic environmental quality monitoring for the functional areas. The noise map is essential for noise monitoring, evaluation and regulation. This paper reviews the Chinese literature on noise maps in the past three decades, particularly concerning noise indexes. Most studies adopted A-weighted equivalent sound pressure level (LAeq), whereas a few investigated noise pollution index (NPI), noise impact index (NII), and index of noise evaluation model (ANEM) by considering the influence of different functional areas, the distribution of people, and both, respectively. However, studies are mostly based on sound energy parameters and rarely have considered the differences in subjective discomfort for the dynamic evolvement of changing populations among different areas and periods. The appropriate noise evaluation index for noise maps, which can reasonably reflect the influence of noise on people in various functional areas, merits further research. Recommendations for future work in this area are presented.

Environmental controls of air-conditioned noise with the aid of the Psychoacoustics Perception Scale (PPS)

It is known that an air-conditioning system is an essential component of modern buildings for maintaining good indoor environmental quality. However, the adverse effect due to air-conditioned noise can offset its benefits. Although several noise indices such as Noise Criteria (NC), Noise Rating (NR), Room Criteria (RC), and A-weighted equivalent continuous sound pressure level (LAeq) have been developed to assess the acceptability of indoor noise environments, the noise feature of the environments and its psychological impacts on the occupants are not comprehensively evaluated. Psychoacoustics Perception Scale (PPS) is a psychometric tool to assess the psychological impacts about general judgment (Evaluation, E), sensitivity to the magnitude (Potency, P), and sensation of the temporal and spectral compositions (Activity, A) of noise on occupants. This study aimed to evaluate the air-conditioning building environments by using the traditional noise indices, psychoacoustic metrics, and the PPS. The significant correlations were found between the objective and subjective data. The results of the study provided the useful knowledge on future designs of the environmental controls of air-conditioned noise.

Variations in sound environment in an urban apartment building: A case study during and after the COVID-19 lockdown

Quiet communities, which are encouraged to maintain a harmonious and tranquil urban living environment, have attracted increasing attention in designing method in recent years. The relevant residential standards specify quiet thresholds with regard to noise pollution issues. However, the variation in height across floors of high-rise buildings and variation with time in sound environments have not been examined in detail. The city of Shanghai experienced a city-wide lockdown to control the spread of COVID-19, showing evidence of quietness and a significant reduction in anthropogenic noise. Here, we conducted noise monitoring in a 14-storey apartment building that was surrounded and shielded by other buildings in a typical urban community during and after the lockdown. The mean value of all 14 floors of equivalent continuous A-weighted sound pressure level (LAeq,T) after lockdown was systematically greater than that during lockdown, with differences of 3.6 and 3.1 dB during the daytime and night-time periods, respectively. We suggest that in practice, it is useful to consider the specific floor or time of day.

A segment-based A-weighted sound propagation model for road traffic noise assessment: A general concept

The propagation model of the road traffic noise established by the Acoustical Society of Japan, the ASJ-RTN Model 2018, directly obtains the A-weighted sound pressure level by assuming specific power spectra of vehicle sources in a single calculation. This is more effective in reducing computational burden than European models, which typically require calculations in eight bands from 63 Hz to 8 kHz. However, the ASJ model has not been generalized enough to deal with an arbitrary terrain profile, contrary to the European models where the handling of a segmented terrain profile is integrated. This will become a major obstacle in realizing noise mapping in Japan. In this paper, a concept of an A-weighted sound propagation model for road traffic noise with integrated handling of a segmented terrain profile is presented. The model combines the segmented modeling of multiple diffractions over a complex profile and the Fresnel weighting of ground characteristics both employed by Harmonoise, the mean plane for ground modeling used in CNOSSOS-EU, and the calculation of the excess attenuation terms following the ASJ model. Preliminary calculation results show that the model agrees reasonably well with finite-difference time-domain simulation results on flat and uniform ground, but still needs investigation for non-flat and nonuniform ground.

Effects of Aircraft Noise on Sleep: Federal Aviation Administration National Sleep Study Protocol.

Aircraft noise can disrupt sleep and impair recuperation. The last U.S. investigation into the effects of aircraft noise on sleep dates back more than 20 years. Since then, traffic patterns and the noise levels produced by single aircraft have changed substantially. It is therefore important to acquire current data on sleep disturbance relative to varying degrees of aircraft noise exposure in the U.S. that can be used to check and potentially update the existing noise policy. This manuscript describes the design, procedures, and analytical approaches of the FAA's National Sleep Study. Seventy-seven U.S. airports with relevant nighttime air traffic from 39 states are included in the sampling frame. Based on simulation-based power calculations, the field study aims to recruit 400 participants from four noise strata and record an electrocardiogram (ECG), body movement, and sound pressure levels in the bedroom for five consecutive nights. The primary outcome of the study is an exposure-response function between the instantaneous, maximum A-weighted sound pressure levels (dBA) of individual aircraft measured in the bedroom and awakening probability inferred from changes in heart rate and body movement. Self-reported sleep disturbance due to aircraft noise is the secondary outcome that will be associated with long-term average noise exposure metrics such as the Day-Night Average Sound Level (DNL) and the Nighttime Equivalent Sound Level (Lnight). The effect of aircraft noise on several other physiological and self-report outcomes will also be investigated. This study will provide key insights into the effects of aircraft noise on objectively and subjectively assessed sleep disturbance.

Variability of small multirotor aircraft noise measurements

Experimental procedures are developed to measure and characterize the variability of noise radiated by small multirotor aircraft during outdoor flight. These procedures were applied to characterize the noise of a Tarot X8 octocopter. Large (up to 10 dB) variations in A-weighted sound pressure level (SPL) are observed between repeated measurements of the same flight conditions. However, the measured peak SPLs are found to be insensitive to changes in flight speed. This results in a reduction of sound exposure level with increasing flight speed. The A-weighted sound exposure level varies by as much as 6 dB across repeated overflights. Variability in noise is assessed both across repeated runs of the same condition and within a run using an array of microphones parallel to the flight track. Variability is found to increase as the distance between the microphone and aircraft increases. Variations within a run are significant (2.2 dB) and are similar to the variation in peak SPLs observed between runs (2.5 dB).

Sound Environment during Dental Treatment in Relation to COVID-19 Pandemic

This study delves into the acoustic environment within dental clinics, particularly focusing on the impact of extraoral suction devices employed for infection control amid the COVID-19 pandemic. The research encompasses a comprehensive investigation, including a questionnaire survey of dental professionals, sound level measurements at suction device openings, acoustic imaging, and a detailed analysis of sound levels and their spectral characteristics during dental procedures. Additionally, ambient sound levels within clinical settings were monitored over two consecutive days. The findings reveal notable observations. Dental professionals expressed concerns regarding increased sound levels and associated distress caused by extraoral suction device operation. Objective measurements identified varying A-weighted sound pressure levels ranging from 86.0 dB to 96.7 dB at suction device openings, highlighting elevated sound pressure levels and a wide frequency range, especially in the vicinity of both the dentist and the patient’s facial area during dental aerosol procedures. On the other hand, for the entire clinical room, the equivalent continuous A-weighted sound pressure level during the consultation hours was not considered problematic. In light of these findings, it becomes evident that there is a pressing necessity to refine the acoustic characteristics of extraoral suction devices to foster a more accommodating acoustic environment for both patients and dental healthcare professionals within dental clinics.

Effects of Audio-Visual Environmental Factors on Emotion Perception of Campus Walking Spaces in Northeastern China

In the context of urban sustainable development and the creation of pedestrian-friendly campus environments, optimizing campus walking spaces has emerged as a central focus in urban planning research. Presently, research in pedestrian environments predominantly adopts a macroscopic perspective, offering limited insights into pedestrians’ subjective experiences and emotional perceptions at a micro level. Therefore, this study conducted on-site experiments in 21 walking spaces across three campuses, utilizing image semantic analysis, multifunctional sound level meter, wearable electrocardiography devices, and the Profile of Mood States (POMS) to collect data separately on audio-visual environmental factors and pedestrians’ emotional states. This study’s findings revealed significant correlations (p < 0.01) among factors such as the Green Visual Index, Spatial Enclosure Index, Sky Visibility Index, Spatial feasibility Index, and Equivalent Continuous A-weighted Sound Pressure Level with physiological and psychological alterations in pedestrians’ emotions. Additionally, the various proportions of audio-visual environmental factors also exerted significant influences on emotions (p < 0.05). The relevant conclusions can provide a reference for optimizing the audio-visual environment of walking space and promoting the sustainable development of the campus. In future research, the effects of audio-visual environments on both emotional and physiological indicators, as well as subjective evaluations, can be explored further.

Noise Reduction Design Method and Validation of Unequal-Pitch Blade Fan for Traction Motor

The traction motor of trains is an essential component that generates the traction force, but it has a significant influence on the indoor and outdoor acoustic environment during the running condition. To enhance passenger comfort and bolster the environmental performance of trains, regulatory standards and specifications governing train noise have imposed elevated criteria on both tonal noise and the overall A-weighted sound pressure level emanating from traction motors. This paper proposes an aerodynamic noise optimization design method based on aerodynamic interference. The objective function of the optimization is defined as the blade-passing frequency (BPF) noise and the A-weighted overall sound pressure level of the traction motor fan. The simulated annealing algorithm is used to optimize the circumferential distribution of the blades. The optimized unevenly spaced blade configuration of the fan effectively reduces the BPF sound pressure level amplitude by 4.6 dBA and the overall A-weighted sound pressure level by 1.2 dBA. The calculation results agree well with the experimental results. The study reveals that unevenly spaced blades contribute to better noise reduction at lower rotational speeds. However, the effect diminishes at higher speeds. The relationship between noise reduction and blade count is nonlinear, suggesting an optimal count for specific speeds.

An Empirical noise model of centrifugal fans with different volute tongues based on Langevin regression

In the context of the rapidly evolving field of building ventilation, fan noise control stands out as a pivotal technology to enhance the quality of life. This study aimed to elucidate the inherent randomness, distinct characteristics, and potential low-dimensional noise structure essential for developing effective noise control methods. In this study, a stochastic dynamics model for the noise of centrifugal fans with various volute tongue structures is constructed using the Langevin regression method and experimental measurements. An empirical noise model capturing the peak characteristics of noise discrete tonal is developed through parametric mode expansion and an empirical mean-field model of turbulent wakes, facilitating accurate noise predictions. The research findings demonstrate the effectiveness of the Langevin equation employing the cubic Stuart-Landau equation and multiplicative noise to predict fan noise across different volute tongue structures. While stochastic dynamics models unavoidably lose the characteristic discrete noise peaks, predictions of the total A-weighted sound pressure level remain within a 2.2% error margin. The stochastic dynamics models applied to centrifugal fan aerodynamic noise and turbulent wakes exhibit striking resemblances, suggesting a fundamental connection between turbulence and noise generation. The extended empirical noise model maintains discrete pitch noise peaks by introducing shift modes, indicating that stronger Langevin deformations correspond to larger translational amplitudes of the shift modes. The advancement of stochastic dynamics and empirical noise models lays a foundational framework for the formulation of effective noise control strategies.