Band Sound Levels Research Articles

Indiscernible noise determination of a military system equipped with an internal combustion engine

The main objective of this paper is to explore the non-detectability criteria of military systems and to determine the indiscernible noise of military systems equipped with internal combustion engines. Non-detectability is one of the critical requirements evaluated for military defense systems and it is defined strictly in MIL-STD-1474E standard. Furthermore, this standard specifies the limits of sound pressure levels conservatively for 1/3 octave bands. Though, the standard does not define indiscernible or inaudible noise levels for events in the presence of background noise. It is also not explicitly well-defined in the existing literature. This study presents a comparison of non-detectability distance defined in MIL-STD-1474E standard and indiscernible noise of a military system extracted from the measured octave band sound levels, which are processed based on sound propagation theory. In this study, several parameters such as atmospheric absorption, geometric spreading, ground effect, terrain type, obstacle existence are included to determine the indiscernible noise level of the military system of interest. The results are compared with the non-detectability distance limits given in the MIL-STD-1474E standard, and it is observed that the proposed method of indiscernible noise, which is defined as extracted sound level should be lower than the background noise, is well-correlated.

Uncertainties of band sound levels when estimated from monochromatic outdoor sound propagation calculations

Octave band and third octave bands sound levels are widely used in environmental acoustics, and most numerical models for outdoor sound propagation estimate them through the combination of several monochromatic calculations. As some of these models can be very time consuming when long range distance calculations are needed, the number of monochromatic calculations performed for each band is often necessarily very limited. That induces uncertainties on the estimate of the noise level of the band that can be large when the spectrum amplitude varies widely inside a band. This is the case for example when interferences due to ground effects occur. The paper presents estimates of these uncertainties depending on frequency band and on source-receiver locations. The uncertainties are evaluated thanks to a quasi Monte-Carlo technique from many calculations using a Rudnick propagation model and a Latin Hypercube Sampling numerical experimental design for input parameters (source-receiver locations). The results provide practical indications on the minimum number of monochromatic calculations to do per band, in order not to exceed a given uncertainty level.

Measured noise levels beneath type B flat metal roof assemblies during rainfall

Flat metal roof assemblies are common in steel building design. Since they can produce high levels of rainfall generated noise, quiet roof assemblies are desirable over noise sensitive spaces. To determine the relative effects of assembly variations, a pair of fixtures were constructed to measure the noise levels beneath 2 x 4 ft sections of selected roof assemblies subjected to rainfall. Each test item was assembled from precut 2 x 4 ft sections of Type B metal roof (with or without a concrete layer), cover boards, and insulation, membrane and ballast as required. The fixtures were equipped with tipping buckets to measure rainfall rate. A microphone located inside each box and connected to a digital recorder, picked up ambient noise, rainfall generated roof assembly noise and the tipping bucket signal. To calibrate the recordings, the sound pressure level of the tipping bucket signal at the recording microphone was measured before testing. Recordings were analyzed to calculate indicated octave band sound power levels versus rainfall rate for the various tested roof assemblies.

Measured noise levels beneath type B flat metal roof assemblies during rainfall

Flat metal roof assemblies are common in steel building design. Since they can produce high levels of rainfall generated noise, quiet roof assemblies are desirable over noise sensitive spaces. To determine the relative effects of design variations, a pair of fixtures were constructed to measure the noise levels beneath 2 × 4 ft sections of selected roof assemblies subjected to rainfall. Each test item was assembled from precut 2 × 4 ft sections of type B metal roof (with or without a concrete layer), cover boards, and insulation, membrane and ballast as required. The fixtures included a tipping bucket to measure rainfall rate. A microphone located inside each fixture and connected to a digital recorder, picked up ambient noise, rainfall generated roof assembly noise, and the tipping bucket signal. To calibrate the recordings, the sound pressure level of the tipping bucket signal was measured at the recording microphone before testing. Recordings are analyzed to calculate indicated octave band sound power levels versus rainfall rate for the various tested roof assemblies. Promising variations for further study are given.

Field Validation of Octave Band Sound Modeling for Wind Turbines

The Sugar Creek Wind Project is a 57-turbine wind farm in Logan County, Illinois, with a capacity of up to 202 megawatts. Preconstruction sound modeling of the final Project layout was conducted in July 2019. Following construction of the Project, postconstruction attended sound measurements were made at 38 sites in the vicinity of Project turbines in September, October, and November 2021. Measured postconstruction sound levels were compared to the octave band sound level limits applicable under the Project's Conditional Use Permit. A comparison of the modeled and background-adjusted measured octave band sound levels for the Project indicate that with the proper modeling parameters, octave band sound levels can be conservatively predicted.

Field validation of octave band sound modeling for wind turbines

The Sugar Creek Wind Project is a 57-turbine wind farm in Logan County, Illinois, with a capacity of up to 202 megawatts. Preconstruction sound modeling of the final Project layout was conducted in July 2019. Following construction of the Project, postconstruction attended sound measurements were made at 38 sites in the vicinity of Project turbines in September, October, and November 2021. Measured postconstruction sound levels were compared to the octave band sound level limits applicable under the Project’s Conditional Use Permit. A comparison of the modeled and background-adjusted measured octave band sound levels for the Project indicate that with the proper modeling parameters, octave band sound levels can be conservatively predicted.

Temperature mediates chorusing behaviour associated with spawning in the sciaenid Argyrosomus regius

Climate change is leading to an increase in the frequency and intensity of daily temperature extremes in aquatic environments, posing a threat to ectothermic animals such as fishes. Temperature shifts can impact their reproductive cycle and behaviour, including acoustic signalling associated with courtship and mating in vocal fishes. Here, we examined the effect of temperature and other environmental factors on spawning-related chorusing behaviour in the meagreArgyrosomus regius. Using an automatic recognition system based on hidden Markov models coupled with one-third octave band sound level analysis, we extracted meagre daily vocal activity over 4 yr of passive acoustic monitoring (PAM) in the Tagus estuary (Portugal). Meagre vocal activity showed a distinct diel pattern, with choruses being most prevalent at dusk. Chorus activity started earlier in years with warmer springs, while the end of the season was concurrent with the rise in water temperature. Circa 70% of daily variations were explained by changes in water temperature. Tidal cycle, lunar phase and changes in daylength did not appear to affect vocal behaviour. Choruses were detected on days with mean water temperature ranging from 15-25°C, with stronger chorusing observed around 18°C. Abrupt temperature changes caused disruption in choruses and likely in associated spawning. This study highlights the importance of temperature to fish reproduction and demonstrates that PAM can be a useful tool for long-term conservation management plans. PAM may also allow us to predict how temperature shifts due to climate change may affect fish reproduction, using vocal fishes as model species.

Duct, duct, goose chase? Revisiting algorithms for duct flow noise

The American Society for Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE) has several practical resources for flow noise prediction. There are reference tables for maximum air velocities for a given background noise rating as well as tables for maximum “free area” speeds for supply diffusers or return registers. For other duct fittings, engineers may use a variety of algorithms to predict octave band sound power levels. Experiments have demonstrated a direct relationship between flow noise and duct size, aspect ratio, and pressure drop. Currently, few prediction methods accurately take these factors into account because the underpinning algorithms are based on a limited set of ductwork sizes. To better understand how these factors impact airflow generated noise, ASHRAE has conditionally approved Work Statement 1919: The effects of duct size and aspect ratio on flow noise in elbows. This paper will review past literature, highlight shortcomings of current prediction methods, and discuss the proposed methodology for upcoming research.

Prediction of one-third-octave band sound and vibration levels from heavy-hard impacts

Noise and vibration due to dropping hard heavy weights is a common source of disturbance and complaint in residential, commercial, and mixed-use building types. The authors and others have worked on developing methodologies to accurately, repeatably, and conveniently measure heavy-hard impact noise and vibration in the field based on a standard weight drop. Separately, systems have been created to measure the force being injected into a building from heavy-hard impact. It has been shown that this force data can be used to successfully predict vibration levels in buildings if in-situ transfer functions are known. In this paper, the authors will present a novel one-third-octave band prediction method using the laboratory force data and a reference impact sheet to predict field performance without the need to measure transfer function. The method is evaluated using both noise and vibration measurements.

Subtraction Analysis for Predicting the Propagation Effects of Aircraft Noise

In 2013, the Federal Aviation Administration and Volpe National Transportation System Center conducted a series of acoustic measurements with a propeller driven aircraft operating in the regions near Houston, Texas. The recorded data on octave band sound levels, aircraft locations, temperature and wind speed profiles were used in the current study to quantify the uncertainties for predicting the propagation effects of aircraft noise. Use of the Aviation Environmental Design Tool (AEDT) was explored for its accuracy and validity in real world scenarios offered by the dataset. The sound exposure level (SEL) data for each section of a flight path was used instead of the time history data for reducing the directivity effect of the sound source due to the change in its relative positions with the receivers. A subtraction-based method was introduced to analyze the propagation effect in which the SELs between two receiver locations were compared. The use of the subtraction method reduces the possible influences of the sound power variations along the flight paths. The measured data for a spiral and a level flight event were presented and the AEDT predictions on the propagation effects were examined in this paper.

Effect of Boundary Layer and Rotor Speed on Broadband Noise from Wind Turbines

Trailing edge surface of aerofoil is an important source of broadband aerodynamic noise production. In this paper, three aerofoil self-noise mechanisms from turbulent boundary layer near trailing edge surface are studied. Numerical computations were performed for a three bladed 2 MW horizontal axis upwind turbine of blade length 37 m and source height of 80 m, for wind speeds of 8-15 m/s. A weighted 1/3rd octave band sound power levels (SPL) are evaluated for receiver located at distance of total turbine height and at 2 m above ground. The results obtained for sound power level using baseline models showed maximum values occurring between 300 Hz and 1 kHz region of spectrum. The trends for BPM model showed a reduction of ~2 dBA near 1 kHz region of spectrum at 10 m/s, but Grosveld’s and Lowson model were identical and agreed over the entire spectrum. The effect of rotational speed on sound power levels using three baseline models are illustrated at a wind speed of 8 m/s for 2 MW turbine. Results showed that for a change of ±10% rotor speed from the rated value, there is an increase of 2 to 6 dBA over the entire sound spectrum due to differences in blade tip speed.

Automated parsing of sound level meter data into artifacts, natural sources, and noise

The National Park Service (NPS) has nearly one million hours of 1/3rd octave band sound level measurements collected at hundreds of sites throughout the system. One of the principal purposes of these data is to measure the background or residual sound level against which all transient sounds are heard. Historically this analysis has depended upon trained listeners to identify which sound sources can be heard in segments of these data. These annotated records were then used to calculate an adjusted median sound level. To pursue a more efficient, automated method to deliver this result, matrix decomposition methods were tested to characterize their capacity to model time series of sound level spectra as low-rank decompositions, including options to account for anomalous events. These methods were combined with sound source identification based on component spectral properties and time weightings to yield promising approaches for automating NPS analyses. These results may also offer options for detecting and removing the effects of pseudonoise due to the turbulence generated by air flowing past the microphone.

Relationship between road surface profiles and 1/3 octave band sound power levels of noise of running vehicles

Relationship between road surface profiles and 1/3 octave band sound power levels of noise of running vehicles

Wayside noise measurement and propagation predictions for four motorcycles categories

Motorcycle noise is distinct from other types of road transportation noise and it varies within this general vehicle type based on design characteristics. One-third octave band sound levels that had been measured for four motorcycles categories (cruiser, sport, dual purpose, and touring) using statistical, isolated pass-by techniques for wayside measurements were analyzed. The spectra are dominated by different frequency components depending on the category and these differences have implications on how sound for different categories propagates over extended distances. This is an important consideration for predicting and mitigating motorcycle noise. To illustrate this, these measurements were used to modify a version of the Federal Highway Administration's Traffic Noise Model. This model was then used to predict noise levels at various distances representative of typical receptor locations for the different motorcycle categories. It is expected that accounting for these differences will aid local, state and federal agencies that wish to improve the management of motorcycle noise in their jurisdictions.

Measurement of flow noise generation and pressure loss of nets and screens

Nets, screens and grids are often used to either reduce or generate turbulence for aeroacoustic testing in wind tunnel facilities. It is hence important that the self noise generated by such devices due to the flow is considerably lower than the noise sources to be examined.In order to obtain a basic understanding of the aerodynamic noise generated by nets and screens, a detailed experimental study was performed on a large number of nets of varying parameters. This included the measurement of the pressure loss and the determination of the sound power generated by the nets. The resulting one third octave band sound power levels were then used to derive a simple empirical prediction model for the noise generated by such devices.

Acoustic and biological trends on coral reefs off Maui, Hawaii

Coral reefs are characterized by high biodiversity, and evidence suggests that reef soundscapes reflect local species assemblages. To investigate how sounds produced on a given reef relate to abiotic and biotic parameters and how that relationship may change over time, an observational study was conducted between September 2014 and January 2016 at seven Hawaiian reefs that varied in coral cover, rugosity, and fish assemblages. The reefs were equipped with temperature loggers and acoustic recording devices that recorded on a 10% duty cycle. Benthic and fish visual survey data were collected four times over the course of the study. On average, reefs ranged from 0 to 80% live coral cover, although changes between surveys were noted, in particular during the major El Nino-related bleaching event of October 2015. Acoustic analyses focused on two frequency bands (50–1200 and 1.8–20.5 kHz) that corresponded to the dominant spectral features of the major sound-producing taxa on these reefs, fish, and snapping shrimp, respectively. In the low-frequency band, the presence of humpback whales (December–May) was a major contributor to sound level, whereas in the high-frequency band sound level closely tracked water temperature. On shorter timescales, the magnitude of the diel trend in sound production was greater than that of the lunar trend, but both varied in strength among reefs, which may reflect differences in the species assemblages present. Results indicated that the magnitude of the diel trend was related to fish densities at low frequencies and coral cover at high frequencies; however, the strength of these relationships varied by season. Thus, long-term acoustic recordings capture the substantial acoustic variability present in coral-reef ecosystems and provide insight into the presence and relative abundance of sound-producing organisms.

Modeling Soundscape Pleasantness Using perceptual Assessments and Acoustic Measurements Along Paths in Urban Context

Mapping the pleasantness of an urban environment is an alternative approach, closer to the city dweller's perception, than standardized sound levels cartography. This study reports on modeling pleasantness in urban context using perceptual assessments and sound measurements for specific locations during an urban walk. These assessments have been collected from four groups of approximately ten participants on 19 different assessment locations, along a 2.1 km-long path traveled in both directions. Simultaneously, 1/3-octave band sound levels and audio were recorded. Perceptual and physical models of pleasantness are proposed for specific locations based on multiple linear regressions. A multilevel analysis was performed, and it is shown that a perceptual model that includes perceived loudness joined to the perceived time of presence of traffic, voices and birds explains 90% of the pleasantness variance due to the sound environment variations. Physical models that include the original acoustic indicators that are most correlated with perceptual variables explain 85% of this variance. Thanks to these models, a unique averaged pleasantness value is defined for each assessment location from the perceptual or physical collected assessments. The Pearson's correlation coefficient between the averaged perceived pleasantness and the modeled values from perceptual assessment reaches r(19) = 0.98, and r(19) = 0.97, with the modeled values from physical measurements. These results make it possible to consider the use of this kind of models in a cartographic context. As the path was traveled in both directions, the presentation-order effect has also been assessed, and it has been found that path direction did not have a significant impact on the pleasantness assessment at specific locations, except when very strong sound environment changes occurred. Finally, the study gives some insights about the retrospective global pleasantness assessment for urban walks. For very short walks between two assessment locations, a recency effect is shown. Nevertheless, this effect doesn't seem to be significant when longer routes are assessed.

Acoustic and biological trends on coral reefs off Maui, Hawaii

Coral reef soundscapes comprise a range of biological sounds. To investigate how the sounds produced on a given reef relate to the species present, 7 Hawaiian reefs that varied in their species assemblages were equipped with acoustic recorders operating on a 10% duty cycle for 16 months, starting in September 2014. Benthic and fish visual surveys were conducted 4 times over the course of the study. Acoustic analyses were carried out in 2 frequency bands (50-1200 Hz and 1.8-20.5 kHz) that corresponded with the spectral features of the major sound-producing taxa on these reefs, fish and snapping shrimp, respectively. In the low-frequency band, the presence of humpback whales (December-May) was the major driver of sound level, whereas in the high-frequency band sound level closely tracked water temperature. On shorter timescales, the magnitude of the diel trend varied in strength among reefs, which may reflect differences in the species assemblages present. Regression trees indicated that, at low frequencies, the relationship between species assemblages and acoustic parameters varied by season; however, at high frequencies, a given reef was generally most like itself over time. Thus, long-term acoustic recordings can capture and distill the substantial acoustic variability present in coral reef ecosystems.

Centerline rumble strip sound level evaluation—Comparison of four designs

Results of sound level monitoring of four alternative centerline sinusoidal rumble strip designs are discussed: a single strip 14 inches wide and a double strip of two 8 inch wide strips 4 inches apart each with depths—3/8 inch or ½ inch. These results supplement those presented at the Pittsburgh 2015 meeting (3aNS5). Tests were performed at 60 mph with three different vehicles—passenger car, pickup truck, and a six-wheel heavy maintenance truck. One-third octave band sound levels were taken 50 and 75 feet from the edge of the roadway, as well as inside the vehicle. Digital audio recordings were also taken. The single 14 inch design with ½ inch depth was recommended for implementation by MnDOT since it provided good driver feedback but less exterior noise than the other designs for passenger cars but also good results for pickup trucks, a significant portion of the vehicle fleet. Based upon an evaluation of alternative rumble strips by motorcycles and bicycles at the MnROAD test facility, the single strip...

Simulated sound in advanced acoustic model videos

The Advanced Acoustic Model (AAM) and other time-step aircraft noise simulation models developed by Wyle can generate video animations of the noise environment. The animations are valuable for understanding details of noise footprints and for community outreach. Using algorithms developed by NASA, audio simulation for jet aircraft noise has recently been added to the video capability. Input data for the simulations consist of AAM’s one-third octave band sound level time history output, plus flight path geometry and ground properties. Working at an audio sample rate of 44.1 kHz and a sample “hop” period of 0.0116 s, a random phase narrow band sample is shaped to match spectral amplitudes. Ground reflection and low frequency oscillation are added to the hops, which are merged into a WAV file. The WAV file is then mixed with an existing animation generated from the same AAM run. The process takes place in near-real time, based on a location that a user selects from a site map. The presentation includes demonstrations of the results for a simple level flyover and for the departure of a high performance jet aircraft from an airbase.