A-weighted Sound Exposure Level Research Articles

On the expert evaluation of potential damage to hearing using A-weighted sound exposure level (LAE)

On the expert evaluation of potential damage to hearing using A-weighted sound exposure level (LAE)

Investigation of speed and altitude effects on sound exposure level calculations for multiple helicopters

International and United States Federal regulations evaluate helicopter acoustic emissions for certification purposes as well as community noise impact assessments. The Sound Exposure Level (SEL) is a commonly used metric that represents the loudness of a single event, with a penalty for duration. For example, a flyover lasting ten seconds can have the same SEL as a five-second duration flyover that is 6 dB higher in peak level. Ten helicopters spanning the light and medium weight classes were modeled using flight test data. They were then virtually flown using the Advanced Acoustic Model at multiple speeds and altitudes. SEL and A-weighted SEL (SELA) were calculated at ground-based observer locations for each condition. Scaling laws with altitude are determined, and cruising airspeeds which result in the minimum SEL are found. Implications for future land-use planning will be discussed, and the relationships are reduced to general or vehicle-specific operational guidance for pilots.

Sonic boom measurements: Practical implications considering ground effects, microphone installation, and weather hardening.

Sonic boom measurements from recent flight tests have provided an opportunity to investigate effects of microphone installation on sonic boom waveforms, spectra, and metric levels in support of NASA X-59 flight test planning. While those flight tests used N-wave aircraft (F-18s), modeling studies were also conducted using source characteristics for a shaped low-boom aircraft. Of particular interest were the effects of receiver height on boom waveforms and metrics at elevated receiver positions, microphone installation, and local ground cover type. Reductions of more than 2 dB in A-weighted sound exposure level and perceived level were shown for 1.6 ft (0.48 m) microphone heights for 35º ray elevation angle. Measured and modeled results are described in this letter.

Requirements for Drone Operations to Minimise Community Noise Impact.

The number of applications for drones under R&D have growth significantly during the last few years; however, the wider adoption of these technologies requires ensuring public trust and acceptance. Noise has been identified as one of the key concerns for public acceptance. Although substantial research has been carried out to better understand the sound source generation mechanisms in drones, important questions remain about the requirements for operational procedures and regulatory frameworks. An important issue is that drones operate within different airspace, closer to communities than conventional aircraft, and that the noise produced is highly tonal and contains a greater proportion of high-frequency broadband noise compared with typical aircraft noise. This is likely to cause concern for exposed communities due to impacts on public health and well-being. This paper presents a modelling framework for setting recommendations for drone operations to minimise community noise impact. The modelling framework is based on specific noise targets, e.g., the guidelines at a receiver position defined by WHO for sleep quality inside a residential property. The main assumption is that the estimation of drone noise exposure indoors is highly relevant for informing operational constraints to minimise noise annoyance and sleep disturbance. This paper illustrates the applicability of the modelling framework with a case study, where maximum A-weighted sound pressure levels and sound exposure levels as received in typical indoor environments are used to define drone-façade minimum distance to meet WHO recommendations. The practical and scalable capabilities of this modelling framework make it a useful tool for inferring and assessing the impact of drone noise through compliance with appropriate guideline noise criteria. It is considered that with further refinement, this modelling framework could prove to be a significant tool in assisting with the development of noise metrics, regulations specific to drone operations and the assessment of future drone operations and associated noise.

Analysis of sonic booms from Falcon 9 booster landings

One drawback to the ability to land boosters of orbital launch vehicles, such as the Falcon 9, is the associated reentry sonic boom. Because of the Falcon 9 booster shape and landing orientation, the observed waveform at the ground contains three shocks (a triple boom), rather than the two associated with a traditional N-wave. To assess the impact of these sonic booms, acoustic data from a Falcon-9 booster landing at Vandenberg Space Force Base are analyzed. The data were collected in Lompoc, CA, at locations 7-14 km away from the landing site. Waveform and spectral characteristics are examined and various metrics, including A-weighted Sound Exposure Levels (ASEL), are calculated. These metrics from the reentry sonic booms are compared with metrics calculated from the launch noise.

Investigating the impact of ambient noise on candidate sonic boom metrics

One goal of NASA’s X-59 flight campaign will be to collect low-amplitude sonic boom data over several communities. The combination of lower-amplitude booms with greater ambient noise could pose challenges in measuring and calculating accurate sonic boom perception metrics intended to be correlated with human annoyance. This study uses two NASA sonic boom flight test and simulated X-59 datasets to investigate the impact of limited measurement bandwidth due to ambient noise for multiple candidate metrics. An estimate of the signal-to-noise ratio spectrum allows for the comparison of metrics calculated with full bandwidth, limited bandwidth, and those calculated by applying a low-pass filter that approximates a noise-free full-bandwidth spectrum. The low-pass filter is chosen to approximately match the expected high-frequency roll-off of the sonic booms. Results indicate that Perceived Level and A-weighted sound exposure level are strongly affected by ambient noise and bandwidth limitations, but that B-weighted sound exposure level is much less affected. These results contribute to community noise test planning by demonstrating the ambient noise impact on candidate sonic boom perception metrics. [Work supported by NASA Langley Research Center through National Institute of Aerospace.]

Comments on "Influences of low-frequency energy and testing environment on annoyance responses to supersonic aircraft noise when heard indoors" [J. Acoust. Soc. Am. 148(1), 414-429 (2020)

Carr, Davies, Loubeau, Rathsam, and Klos [J. Acoust. Soc. Am. 148, 414-429 (2020)] found that indoor annoyance caused by sonic booms may be predicted from the A-weighted sound exposure level and the heaviness of the booms. Moreover, they suggest that, irrespective of the outdoor-to-indoor sound reduction, indoor annoyance may be predicted from outdoor sound levels. The present paper shows that their data to some extent also support a model in which the contribution of heaviness is level-dependent and that data reported in the literature point out that it is unlikely that indoor annoyance is independent of the degree of façade attenuation.

An experiment on the feeling of separation when multiple aircraft noises are overlapped

In order to calculate the A-weighted single event sound exposure level () of aircraft noise, the following method is described in the manual for aircraft noise measurement in Japan. Firstly a time-section, which is the range between two points where the noise level is 10 dB lower than the maximum noise level (), should be identified, and secondly the energy within the section is integrated. This method can easily be applied to the single event noises. When multiple aircraft noises are overlapped simultaneously, there are cases where cannot be calculated adequately by this method. In such cases, it is required to record the number of aircraft noises in the field measurements. However, even in the case of manned measurement, it is not easy to separate sound sources just by listening to the sound. A pilot study of the psychoacoustic experiment was conducted using the stimuli where multiple aircraft noises were overlapped in order to find what condition is needed so that multiple aircraft noises were separately perceived. It was suggested that a considerable time interval was needed so that people felt the separation between aircraft noises only with auditory information.

Relationships between ratings and calculated loudness values for sonic booms at low levels

Due to progress in aircraft design, the sonic boom produced by supersonic aircraft may be reduced considerably in the future and the subjective response of humans to future low sonic boom signatures is currently under investigation. In the frame of the RUMBLE project, loudness and short-term ratings of different recordings and simulations of classical booms and potential future boom sounds were collected. The time signals of the signatures were differing in shape but were confined in maximum overpressure and the A-weighted sound exposure level (ASEL) to the range foreseen for future low boom aircraft. Besides a high correlation with the ASEL, the short-term annoyance ratings were also highly correlated to the loudness ratings, suggesting that loudness was the underlying factor for short-term annoyance in the laboratory experiments. Therefore, loudness values were calculated with loudness models from the current ISO 532-1 and 532-2 standard in an attempt to predict the annoyance ratings. The correlation coefficients between short-term annoyance ratings and loudness model values are similar to those between ratings and level based measures (e.g., weighted SELs). For the loudness model according to the ISO 532-1 standard, the correlation coefficient is even slightly higher that than for ASEL.

Investigation of sonic boom waveforms and metrics at elevated receiver locations

Microphones used for aircraft noise measurements are sometimes positioned above local ground level, for example to accommodate environmental protection or to comply with certification regulations. Acoustic waves reflected from the ground can interfere with waves propagating directly to elevated receivers. A modeling study was conducted of sonic boom waveforms received at ground level versus at elevated positions, using source characteristics for an early X-59 low-boom aircraft configuration (C609) and a variety of atmospheric conditions. Ground impedance effects from different ground cover types were also considered. Among several acoustic metrics, it was found that perceived level of loudness (PL) and A-weighted sound exposure level were in general the most sensitive to differences due to receiver position. Location within the boom carpet also affected receiver levels based on the angle between the incoming ray and the ground: the difference between metrics at ground and elevated receivers was generally higher at undertrack locations where that angle was largest. Depending on atmospheric conditions and receiver location within the carpet, predicted PL at an elevated receiver was lower than the level at the ground by up to 5.0 dB for a receiver height of 4 ft and 2.2 dB lower for a 1.6-ft receiver.

Loudness and short-term annoyance of sonic boom signatures at low levels.

Supersonic aircraft produce a sonic boom when flying faster than the speed of sound. To rule out detrimental effects for inhabitants of overflown areas, civil supersonic flights (like the Concorde) were only allowed to fly at supersonic speed when over water. Due to the progress in aircraft design, the supersonic boom may be reduced considerably in the future. In this study, listening tests were carried out with a variety of low boom simulations and conventional sonic boom signatures in a similar level range. Participants rated the loudness and the short-term annoyance of 24 sonic boom signals, which differed in terms of the signature shape and maximum pressure but were confined to a range of A-weighted sound exposure levels around 60 dB(A). The results showed main effects of signature and relative level variation as well as an interaction of the two. Correlation coefficients between the ratings and sound exposure levels were highest for A-weighted sound exposure levels compared to other frequency weightings. Contrary to our expectations, the provision of background information about the nature of the presented sound sources had no statistically significant influence on the ratings.

Erratum: Stability of sonic boom metrics regarding signature distortions in atmospheric turbulence [J. Acoust. Soc. Am. 141(6), EL592-EL597 (2017)

In Doebler and Sparrow [J. Acoust. Soc. Am. 141(6), EL592-EL597 (2017)], a collection of five sonic boom metrics were analyzed to see which was the most stable in atmospheric turbulence. After publication, a mistake in one metric calculation was discovered that alters a portion of the results from that work. The purpose of this note is to correct those results-replacing one figure and commenting on another. The correction indicates that the Indoor Sonic Boom Annoyance Predictor (ISBAP) is a stable metric in regards to turbulence. ISBAP and B-weighted Sound Exposure Level (BSEL) are found to be similarly stable. E-weighted Sound Exposure Level (ESEL) is the next most stable followed by Steven's Mark VII Perceived Level (PL) and A-weighted Sound Exposure Level (ASEL).

Incident Angle Correction Algorithm For Impulse Noise Injury Assessment.

We developed an empirical algorithm to account for the effect of the change in the A-weighted sound exposure level (SELA) as a result of the change in angle of incidence (AoI) of the impulse noise on the prediction of hearing loss. The product is the upgraded software tool, Auditory 4.5 that incorporates the incident angle correction algorithm. The SELA calculated from free-field pressure data is used as the dose metric that was corrected for AoI. The angle-dependent eardrum pressure was measured by performing shock tube tests with the Acoustical Testing Fixture varied over a wide range of orientation angles. The yaw angle was varied from 0 to 360° and the pitch angle from -60° to +90° in 15° steps. The algorithm was constructed by calculating a correction factor, ΔSELA for any given AoI at the ear relative to the SELA at normal incidence. The ΔSELA values were applied to correct the dose values to predict injury for all AoI. A three-dimensional contour of ΔSELA as a function of the AoI was produced. The largest ΔSELA was 9.81 dB at pitch = -15° and yaw = 255°. ΔSELA values compared well against available benchmark data. A new capability has been incorporated in Auditory 4.5 to predict the effects of AoI on impulse noise injury.

Impulse Noise Injury Model.

The new Auditory 4.0 model has been developed for the assessment of auditory outcomes, expressed as temporary threshold shift (TTS) and permanent threshold shift (PTS), from exposures to impulse noise for unprotected ears, including the prediction of TTS recovery. Auditory 4.0 is an empirical model, constructed from test data collected from chinchillas exposed to impulse noise in the laboratory. Injury outcomes are defined as TTS and PTS, and Auditory 4.0 provides the full range of TTS and PTS dose-response curves with the risk factor constructed from A-weighted sound exposure level. Human data from large weapons noise exposure was also used to guide the development of the recovery model. Guided by data, a 28-dBA shift was applied to the dose-response curves to account for the scaling from chinchillas to humans. Historical data from rifle noise tests were used to validate the dose-response curves. New chinchilla tests were performed to collect recovery data to construct the TTS recovery model. Auditory 4.0 is the only model known to date that provides the full TTS and PTS dose-response curves, including a TTS recovery model. The model shows good agreement with historical data.

Nocturnal boundary layer profiles and measured frequency dependent influence on sound propagation

During four evenings including one night the sound propagation up to a distance of 200m south and north of a railway line was measured and the sound exposure level difference between the distances 25 and 200m from a railway line was calculated. At the same time the meteorological situation was measured with a tethered balloon up to a height of 100m. These measurements were compared with calculated wind and temperature profiles and a reasonable fit of the measured with the theoretical profiles were found.The A-weighted sound exposure level differences were correlated with the effective sound speed gradient with respect to atmospheric stability. In the case of upwind sound propagation a difference of the A-weighted sound level in the range of 10dB between stable and not stable (adiabatic and instable) meteorological situation was found (7dB in the frequency range between 315 and 3150Hz) and in the case of downwind sound propagation in the range of 3dB(A).The stability of the nocturnal layer is expressed with the Obukhov length L which includes (in the bulk definition) a relation of the wind speed gradient to the temperature gradient. The effective sound speed gradient includes the sum of the wind speed gradient and temperature gradient. The main result is that the description of sound propagation should be improved by use of the Obukhov length to include the stability effects of the atmosphere which is especially necessary in the case of upwind sound propagation during the nocturnal boundary layer.

Enhanced awakening probability of repetitive impulse sounds

In the present study relations between the level of impulse sounds and the observed proportion of behaviorally confirmed awakening reactions were determined. The sounds (shooting sounds, bangs produced by door slamming or by container transshipment, aircraft landings) were presented by means of loudspeakers in the bedrooms of 50 volunteers. The fragments for the impulse sounds consisted of single or multiple events. The sounds were presented during a 6-h period that started 75 min after the subjects wanted to sleep. In order to take account of habituation, each subject participated during 18 nights. At equal indoor A-weighted sound exposure levels, the proportion of awakening for the single impulse sounds was equal to that for the aircraft sounds. The proportion of awakening induced by the multiple impulse sounds, however, was significantly higher. For obtaining the same rate of awakening, the sound level of each of the successive impulses in a fragment had to be about 15-25 dB lower than the level of one single impulse. This level difference was largely independent of the degree of habituation. Various explanations for the enhanced awakening probability are discussed.

Study on the effect of sound duration on the annoyance of helicopter noise by applying a technique of time compression and expansion of sound signals

The number of helicopter operations has rapidly increased during the last 20 years in Japan. Helicopter noise sounds different from other aircraft; the waveform of the sound pressure is impulsive and the signal duration is relatively long. The Environmental Agency of Japan implemented new guidelines for evaluating noise exposure around small airports, including heliports, in 1990. This study was executed in connection with the development of provisional guidelines. Psychoacoustic experiments were carried out to identify an evaluation index for helicopter noise. In order to examine the effect of duration independently, we not only used original sound recordings, but also synthesized sound signals. The durations of these sound signals were time compressed or expanded without degrading the quality of the original sound recording. The test results show that the effect of duration is significant, and that the A-weighted sound exposure level is a better index than the maximum A-weighted sound pressure level for the evaluation of helicopter noise.

Estimates of the auditory risk from outdoor impulse noise I: Firecrackers

Firecrackers are common impulse noise exposures in the United States. In this study, impulses produced outdoors by consumer firecrackers were recorded, described, and analyzed with respect to the amount of the auditory risk they pose to the unprotected listener under various listening conditions. Risk estimates were obtained using three contemporary damage risk criteria (DRC), including a waveform parameter-based approach (peak SPL and B duration), an energy-based criterion (A-weighted sound exposure level and equivalent continuous level), and a physiological model (the AHAAH model developed by Price and Kalb). Results from these DRC were converted into numbers of maximum permissible unprotected exposures to facilitate comparison. Acoustic characteristics of firecracker impulses varied with the distance, but only subtle differences were observed across firecrackers. Typical peak levels ranged between 171 dB SPL at 0.5 m and 142 dB SPL at 8 m. Estimates of the auditory risk did not differ significantly across firecrackers, but varied with the distance. Vast differences in maximum permissible exposures were observed, and the directions of the differences varied with the level of the impulse. Typical estimates of maximum permissible exposures ranged between 0 and 2 at 0.5 m and between 31 and 227,000 at 8 m. Unprotected exposures to firecracker impulses should be limited or avoided entirely if the firecrackers are ignited in batches within 8 m of the listener. Differences across DRC are inconsequential at 0.5 m, but have substantial implications at distances of 1 m and more.

충격성 소음에 대한 주관적 반응 - 건설공사장 소음을 중심으로 -

【This research presents a laboratory study on subjective response of impulsive sound caused by construction site (breaker and blasting). The sources are sampled from outdoor noise and their levels range from 40 to 75 dBA at the interval of 5 dBA. The noise unit is based on A-weighted sound exposure level(ASEL; $L_{AE}$ ). To make equal ASEL of listening level, finite impulse response(FIR) filter is applied to the originally sampled source to include the effect of propagation attenuation. Sixty-three subjects, forty-two males and twenty-one female, between 18 and 29 years of age, participated in the experiment. The evaluation method of jury test adopted a semantic difference method(SDM). In the test results for impulsive noise, the subjective response of blasting noise was higher than that of breaker noise. The result of %HA that has been combined responses of the three methods except for pink-noise was executed by regression analysis and was shown as the following equation.: $%HA=746.53/(1+{\exp} (L_{AE}-93.3))+0.34$ .】

Modeling of the roundabout noise impact

A roundabout is a very popular tool used by town planners for carrying smooth and stationary road traffic flow. In this study it is shown that the replacement of a classical road intersection by a roundabout, under certain conditions, may produce a traffic noise decrease. These conditions are expressed in terms of the roundabout speed and the receiver location. The A-weighted sound exposure level is used to describe noise reduction.