Ambient Sound Levels Research Articles

Sources and levels of ambient ocean sound near the Antarctic Peninsula.

Arrays of hydrophones were deployed within the Bransfield Strait and Scotia Sea (Antarctic Peninsula region) from 2005 to 2009 to record ambient ocean sound at frequencies of up to 125 and 500 Hz. Icequakes, which are broadband, short duration signals derived from fracturing of large free-floating icebergs, are a prominent feature of the ocean soundscape. Icequake activity peaks during austral summer and is minimum during winter, likely following freeze-thaw cycles. Iceberg grounding and rapid disintegration also releases significant acoustic energy, equivalent to large-scale geophysical events. Overall ambient sound levels can be as much as ~10–20 dB higher in the open, deep ocean of the Scotia Sea compared to the relatively shallow Bransfield Strait. Noise levels become lowest during the austral winter, as sea-ice cover suppresses wind and wave noise. Ambient noise levels are highest during austral spring and summer, as surface noise, ice cracking and biological activity intensifies. Vocalizations of blue (Balaenoptera musculus) and fin (B. physalus) whales also dominate the long-term spectra records in the 15–28 and 89 Hz bands. Blue whale call energy is a maximum during austral summer-fall in the Drake Passage and Bransfield Strait when ambient noise levels are a maximum and sea-ice cover is a minimum. Fin whale vocalizations were also most common during austral summer-early fall months in both the Bransfield Strait and Scotia Sea. The hydrophone data overall do not show sustained anthropogenic sources (ships and airguns), likely due to low coastal traffic and the typically rough weather and sea conditions of the Southern Ocean.

Tuning the cognitive environment: Sound masking with “natural” sounds in open-plan offices

With the gain in popularity of open-plan office design and the engineering efforts to achieve acoustical comfort for building occupants, a majority of workers still report dissatisfaction in their workplace environment. Office acoustics influence organizational effectiveness, efficiency, and satisfaction through meeting appropriate requirements for speech privacy and ambient sound levels. Implementing a sound masking system is one tried-and-true method of achieving privacy goals. Although each sound masking system is tuned for its specific environment, the signal—random steady state electronic noise, has remained the same for decades. This session explores how “natural” sounds may be used as an alternative to this standard masking signal employed so ubiquitously in sound masking systems in the contemporary office environment. As an unobtrusive background sound, possessing the appropriate spectral characteristics, this proposed use of “natural” sounds for masking challenges the convention that masking sounds should be as meaningless as possible. Based on psychophysical data and a sound-field analysis through an auditory model, we hypothesize that “natural” sounds as masking sounds have the ability (with equal success as conventional masking sounds) to meet standards and criteria for speech privacy while enhancing cognitive functioning, optimizing the ability to concentrate, and increasing overall worker satisfaction.

Wind-induced noise based upon stability dependent turbulent velocity spectrum models

The ambient sound level is an important datum for noise control, quantifying soundscapes, and remote detection. For low acoustic frequencies and fast enough wind speeds, wind-induced noise contributes largely to the measured ambient sound spectrum. Predictive models for wind-induced noise are based upon an empirical relationship between fluctuating pressure, mean wind speed, and the fluctuating streamwise wind velocity. A wind noise model developed by Van den Berg [Van den Berg, G. P., J. Acoust. Soc. Am. 119(2), 824–833, 2006] is derived from a turbulent velocity spectrum, which is applicable for neutral atmospheric stability and flat homogeneous terrain. In this work, several other wind noise models are formulated based upon different turbulent velocity spectrum models. The turbulent velocity spectrum models take into account atmospheric stability, with varying degrees of complexity. Differences in predicted wind noise levels among the models show nearly a 3 dB spread for some atmospheric conditions. A ...

Changes in ambient sound levels observed in relation to the operational status of the Mesa Wind Project Site

Type 1 sound level measurements and continuous audio recordings were obtained from two sites near the Mesa Wind Project Site (MWPS), 100 m and 1500 m from the nearest turbine. The sites were upwind of the turbines. Unexpectedly, MWPS ceased operating 29 days after this project began; data were collected for an additional 127 days. Contrasts in hourly summaries of 1 second 1/3rd octave sound level measurements, controlled for hourly mean wind speed, revealed the contributions of rotating blades. For the near site, at wind speeds below 5 m/s, 1/3rd octave band levels increased starting at about 100 Hz, with distinct spectral peaks appearing between 400 Hz and 2000 Hz. These spectral peaks were less prominent when hourly mean wind speed was 5 m/s or greater. At the far site, small increases in sound level were observed for 1/3rd octave bands at 1 kHz and below when the blades were turning. The levels measured in this study will be compared with levels measured at NPS sites, to evaluate distances at which operational wind farms might affect park acoustical environments.

Studies on the Impact of Road Traffic Noise inside Selected Schools of Tiruchirappalli City, Tamilnadu, India

Traffic noise is one of the major factors causing noise pollution in schools, interfering with learning and teaching activities. School going children are reported to have difficulty in processing the acoustic signals that are presented in noisy environment. The present study provides a reliable estimate of the decibel levels inside chosen class rooms of three selected schools of Tiruchiurapalli, Tamilnadu, India. The students and teachers of all the above schools felt that their school environments were noisy which interfered with their learning / teaching activities. Based on the self reported health status, audiometric tests were conducted on selected students suspected to have hearing problems, which revealed that the chosen children suffer from mild to moderate hearing impairment. In all the schools studied, the ambient sound levels were found to be above the threshold limit of 50 dB (A) for a silent zone prescribed by the Central Pollution Control Board, India.

The Sound of Tropical Cyclones

Abstract Underwater ambient sound levels beneath tropical cyclones were measured using hydrophones onboard Lagrangian floats, which were air deployed in the paths of Hurricane Gustav (2008) and Typhoons Megi (2010) and Fanapi (2010). The sound levels at 40 Hz–50 kHz from 1- to 50-m depth were measured at wind speeds up to 45 m s−1. The measurements reveal a complex dependence of the sound level on wind speed due to the competing effects of sound generation by breaking wind waves and sound attenuation by quiescent bubbles. Sound level increases monotonically with increasing wind speed only for low frequencies (<200 Hz). At higher frequencies (>200 Hz), sound level first increases and then decreases with increasing wind speed. There is a wind speed that produces a maximum sound level for each frequency; the wind speed of the maximum sound level decreases with frequency. Sound level at >20 kHz mostly decreases with wind speed over the wind range 15–45 m s−1. The sound field is nearly uniform with depth in the upper 50 m with nearly all sound attenuation limited to the upper 2 m at all measured frequencies. A simple model of bubble trajectories based on the measured float trajectories finds that resonant bubbles at the high-frequency end of the observations (25 kHz) could easily be advected deeper than 2 m during tropical cyclones. Thus, bubble rise velocity alone cannot explain the lack of sound attenuation at these depths.

Influence of Ambient Sound Fluctuations on the Crossing Decisions of Pedestrians who Are Visually Impaired: Implications for Setting a Minimum Sound Level for Quiet Vehicles

Introduction Following the passage of the Pedestrian Safety Enhancement Act in the United States, the National Highway Traffic Safety Administration is setting a minimum sound level for hybrid and battery electric vehicles. With an aim to aid this effort, the present study investigated the timing and performance of critical street-crossing decisions by pedestrians who are visually impaired (that is, those who are blind or have low vision) at selected intersections. Methods Fourteen visually impaired adults with typical hearing along with a sighted experimenter made street-crossing decisions by indicating when they would initiate crossing using radio controller handsets. Participants’ decisions were compared with the sighted experimenter's decisions to determine the level of their risk. Results At the residential intersection, the percentage of risky crossing decisions by participants was significantly lower when the decisions were made at lower ambient sound levels (M = 8.9%, SD = 6.9%) than when they were made at higher ambient sound levels (M = 35.3%, SD = 21.2%), p < .001. The participants were able to make significantly fewer risky crossing decisions during the windows of time when the ambient sound level was lower at the major-and-minor-street intersection as well ( p = .001). Discussion Participants were often able to take advantage of the troughs in ambient sound for making street-crossing decisions, and the decisions made in lower ambient sound level conditions were generally less risky than those made in higher ambient sound level conditions. Implications for practitioners Given the finding that the level of ambient sound detected when participants made crossing decisions was much lower than the average ambient sound level at a given intersection, as long as there are noticeable dips in ambient sound, average ambient sound level at a given intersection may not be the most relevant measure of background sound level when determining a minimum sound level for the hybrid and electric vehicles.

A geospatial model of ambient sound pressure levels in the contiguous United States.

This paper presents a model that predicts measured sound pressure levels using geospatial features such as topography, climate, hydrology, and anthropogenic activity. The model utilizes random forest, a tree-based machine learning algorithm, which does not incorporate a priori knowledge of source characteristics or propagation mechanics. The response data encompasses 270 000 h of acoustical measurements from 190 sites located in National Parks across the contiguous United States. The explanatory variables were derived from national geospatial data layers and cross validation procedures were used to evaluate model performance and identify variables with predictive power. Using the model, the effects of individual explanatory variables on sound pressure level were isolated and quantified to reveal systematic trends across environmental gradients. Model performance varies by the acoustical metric of interest; the seasonal L50 can be predicted with a median absolute deviation of approximately 3 dB. The primary application for this model is to generalize point measurements to maps expressing spatial variation in ambient sound levels. An example of this mapping capability is presented for Zion National Park and Cedar Breaks National Monument in southwestern Utah.

Is low frequency sound level uniformly increasing on a global scale?

Deep water ambient sound level increases have been documented in the eastern North Pacific Ocean over the past 60 years. It remains unclear whether this increasing trend is observed in other regions of the world. In this work, data from the Comprehensive Nuclear Test Ban Treaty Organization International Monitoring System (CTBTO IMS) were used to examine the rate and direction of low frequency sound level change over the past decade in the Indian, South Atlantic, and Equatorial Pacific Oceans. The sources contributing to the overall sound level patterns differed between the regions. The dominant source observed in the South Atlantic was sound from seismic air gun surveys, while shipping and biologic sources contributed more to the acoustic environment at the Equatorial Pacific location. Unlike the increasing trend observed in the NE Pacific, sound levels over the past 5–6 years in the Equatorial Pacific were decreasing. Decreases were also observed for specific sound level parameters and frequency bands in the South Atlantic Ocean. Based on these observations, it does not appear that low frequency sound levels are increasing in all regions of the worlds' oceans. [Work supported by the Office of Naval Research.]

The Importance of Ambient Sound Level to Characterise Anuran Habitat

Habitat characterisation is a pivotal step of any animal ecology study. The choice of variables used to describe habitats is crucial and need to be relevant to the ecology and behaviour of the species, in order to reflect biologically meaningful distribution patterns. In many species, acoustic communication is critical to individuals’ interactions, and it is expected that ambient acoustic conditions impact their local distribution. Yet, classic animal ecology rarely integrates an acoustic dimension in habitat descriptions. Here we show that ambient sound pressure level (SPL) is a strong predictor of calling site selection in acoustically active frog species. In comparison to six other habitat-related variables (i.e. air and water temperature, depth, width and slope of the stream, substrate), SPL had the most important explanatory power in microhabitat selection for the 34 sampled species. Ambient noise was particularly useful in differentiating two stream-associated guilds: torrents and calmer streams dwelling species. Guild definitions were strongly supported by SPL, whereas slope, which is commonly used in stream-associated habitat, had a weak explanatory power. Moreover, slope measures are non-standardized across studies and are difficult to assess at small scale. We argue that including an acoustic descriptor will improve habitat-species analyses for many acoustically active taxa. SPL integrates habitat topology and temporal information (such as weather and hour of the day, for example) and is a simple and precise measure. We suggest that habitat description in animal ecology should include an acoustic measure such as noise level because it may explain previously misunderstood distribution patterns.

Changes in 63 Hz third-octave band sound levels over 42 months recorded at four deep-ocean observatories

The growing scientific and societal concerns about the effects of underwater sound on marine ecosystems have been recently recognised through the introduction of several international initiatives, like the International Quiet Ocean Experiment, aimed at measuring the environmental impact of ocean noise on large spatial and temporal scales. From a regulatory perspective, the European Marine Strategy Framework Directive includes noise (and other forms of energy) as one of eleven descriptors of good environmental status of Europe's seas. The directive requires member states to monitor trends in annually averaged sound. The Laboratory of Applied Bioacoustics has developed a software package that measures sound levels and monitors acoustic sources in real-time; this software was used for the LIDO project (www.listentothedeep.com), which originated from the European Seafloor Observatory Network of Excellence (ESONET-NoE; www.esonet-noe.org). The system is currently operating worldwide from several wired and radio-linked observatories. The CTBTO (Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization) has made available years of data from hydroacoustic stations to look for ambient sound trends and to detect cetacean presence. Here, we present the analysis of four CTBTO platforms (located in the Pacific, Atlantic and Indian oceans), covering 42months of data, intended to detect annual and monthly changes or trends in the ambient sound levels.

Detection and Classification of Motor Vehicle Noise in a Forested Landscape

Noise emanating from human activity has become a common addition to natural soundscapes and has the potential to harm wildlife and erode human enjoyment of nature. In particular, motor vehicles traveling along roads and trails produce high levels of both chronic and intermittent noise, eliciting varied responses from a wide range of animal species. Anthropogenic noise is especially conspicuous in natural areas where ambient background sound levels are low. In this article, we present an acoustic method to detect and analyze motor vehicle noise. Our approach uses inexpensive consumer products to record sound, sound analysis software to automatically detect sound events within continuous recordings and measure their acoustic properties, and statistical classification methods to categorize sound events. We describe an application of this approach to detect motor vehicle noise on paved, gravel, and natural-surface roads, and off-road vehicle trails in 36 sites distributed throughout a national forest in the Sierra Nevada, CA, USA. These low-cost, unobtrusive methods can be used by scientists and managers to detect anthropogenic noise events for many potential applications, including ecological research, transportation and recreation planning, and natural resource management.

Computing cumulative sound exposure levels from anthropogenic sources in large data sets

The goal of many underwater acoustic environmental assessments is to characterize the soundscape in an area before, during, or after an anthropogenic activity. The assessment determines the range of baseline noise levels from natural and anthropogenic sources and the contribution of the new anthropogenic activity. The noise levels are considered in aggregate for possible effects on the environment. It is accepted that the effects of anthropogenic noise on marine life depend on the intensity and duration of exposure, the frequency content of the sound relative to the hearing abilities of the species, and the behavior context of the species exposed to the sounds. A growing body of scientific evidence is being analyzed to establish threshold sound levels and dose-response curves for injury or behavioral disturbance effects to marine life. Recent research is also raising new questions about the most appropriate ways to compute ambient sound levels and exposure metrics. In this paper, we present our methods for quantifying ambient sound levels and anthropogenic sound levels from shipping and seismic survey activities in large data sets. We also make recommendations on how to estimate background sound levels in the presence of these sound sources.

Development of a real time compliance system for wind farms regulated by ambient-relative noise standards

Some noise level regulations in the U.S. require wind turbine farms to not exceed the ambient sound levels at nearby residences by more than a fixed amount. For the project discussed herein, compliance with such a regulation requires curtailment of turbine operations to some degree at times when turbine operations are at or near maximum, atmospheric conditions are conducive to sound propagation, and sound from other sources including vegetation rustle are at a minimum. Based on the analysis of months of time-synchronized sound, meteorological, and operations data, a system was developed to assess compliance on a real-time, ongoing basis. The primary element in the determination of compliance is the shape of the one-third octave band spectrum at the residence, augmented by ground and hub-height meteorological conditions, and wind farm operations information. Without the spectral filter, curtailment would need to take place under a broader array of meteorological conditions to ensure compliance, which would result in loss of power generation revenue. This paper will describe the data collection and analysis methods, the development of the spectral filter, and the results of field testing including both the partial and entire shut down of the wind farm.

The effects of environmental noise and infant position on cerebral oxygenation.

To assess how different infant positions and peak sound levels affected cerebral oxygen saturation over time. Twenty-four premature infants who were born less than 32 weeks' gestational age without congenital cardiac, neurologic, and gastrointestinal anomalies. Repeated-measures design with the first observation between 2 and 48 hours of life; once again between 49 and 96 hours of life; on day of life 7; and every 7 days thereafter until discharge home, transfer to another hospital, or 40 weeks postmenstrual age, whichever came first. Continuous sound levels (decibels) were obtained and 2 infant positions were performed while measuring cerebral oxygen saturation during 40-minute observation periods. Effect of peak sound and differences in infant position on cerebral oxygen saturation. Peak sound levels 5 dB above the average ambient sound level did not significantly change cerebral oxygen saturation values. Differences in cerebral oxygenation were significantly less when infants were changed from a supine, head midline position to a right lateral, 15° head elevation compared with a left lateral, 0° elevation position. Aspects of the current neonatal intensive care unit environment do not appear to affect cerebral oxygen saturation.

A geospatial model of ambient sound pressure levels in the continental United States

There has been much effort in the US and worldwide to measure, understand and manage natural soundscapes which are often complex due to a multitude of biological, geophysical, and anthropogenic influences. The sound pressure level is a time and space varying quantity that represents the aggregate of present sources. This work presents a predictive model relating seasonal sound pressure levels to geospatial features such as topography, climate, hydrology and anthropogenic activity. The model utilizes random forest, a tree based machine learning algorithm, which does not explicitly incorporate any apriori knowledge of acoustic propagation mechanics. The response data encompasses 271,979 hours of acoustical measurements from 192 unique sites located in National Parks across the contiguous United States. Cross validation procedures were used to evaluate model performance and identify GIS explanatory variables with predictive power. Using the model, the effect of individual explanatory variables on sound pressure level can be isolated and quantified revealing trends across environmental gradients. An example application of projecting predicted sound pressure levels across the Olympic peninsula is discussed. Because many wildlife habitats, geological processes, and anthropogenic impacts occur on a regional scale, the extent of acoustical analyses must be on similar scales.

Detection of Quiet Vehicles by Blind Pedestrians

AbstractThis paper examines participants who are blind, with and without normal hearing, regarding detection of forward approaching and backing vehicles operating in electric mode (identified in this paper as quiet vehicles) under low speed conditions. Testing under low ambient sound conditions involved evaluation of internal combustion engine vehicles, hybrid vehicles operating in electric mode (EM), and the same hybrid vehicles operating in EM but with five different artificially generated sounds. Three of the five artificial sounds improved detection relative to the internal combustion engine condition for both forward and backward detection tasks. Regression analysis indicated that significant predictors of forward detection performance include average wind speed, amplitude modulation of the signal, hearing loss in the 500 Hz range, vehicle velocity, minimum ambient sound level, and overall vehicle sound level in units of A-weighted decibels. The corresponding analysis for backward detection indicated...

Ambient habitat noise and vibration at the Georgia Aquarium

Underwater and in-air noise evaluations were completed in performance pool systems at Georgia Aquarium under normal operating conditions and with performance sound tracks playing. Ambient sound pressure levels at in-pool locations, with corresponding vibration measures from life support system (LSS) pumps, were measured in operating configurations, from shut down to full operation. Results indicate noise levels in the low frequency ranges below 100 Hz were the highest produced by the LSS relative to species hearing thresholds. The LSS had an acoustic impact of about 10 dB at frequencies up to 700 Hz, with a 20 dB re 1 μPa impact above 1000 Hz.

Proving a facility complies with noise regulations

This paper examines the difficulties associated with proving compliance with environmental noise regulations. Topics include determining pre-existing background sound, post-construction measurements during facility operations, and balancing corporate rights with neighborhood expectations. When a new facility is built in a quiet neighborhood, noise complaints are commonplace. The new facility is required to prove compliance with the local noise regulation. Compliance measurements must be made when the facility cannot be shut down and ambient sound levels are unknown. A statistical analysis of the pre-existing background sound often suggests the probability of proving compliance is minimal. In addition, bias toward/against one party in the dispute can have significant ramifications.

Examination of valued attributes of low sound level environments

The introduction of new noise sources into rural environments presents a number of unique community response challenges not typically encountered in urban and suburban environments. Low ambient sound levels combined with intermittently (rather than continuously) audible anthropogenic ambient contributors create unique soundscapes. Residents appear to value many attributes of these soundscapes and wish to preserve and protect them. Application of existing standards and guidelines (quantitative or nuisance-based) often does not meet resident expectations of protection. This paper examines a number of the valued attributes. It then asks questions about noise policy, resident expectations, adequacy of existing standards, source and ambient noise quantification, and the masking of valued attributes by a new noise source. It concludes with a list of issues that bear close examination in order to set future noise impact guidelines for low-ambient environments.