Octave 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.

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.

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.

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.

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.

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.

Documenting the soundscape of a historic working farm.

A working 1880’s farm is the focus of an exploration to provide an acoustical record of historical sounds that once comprised the soundscape. Long term acoustical measurements (including overall A-weighted sound levels, minimum and maximum levels taken once per minute, SEL, statistical metrics, and day/night sound levels), short term measurements (including overall A-weighted and 1/3 octave band sound levels of specific acoustic events), WAV recordings, and video footage are used to analyze typical historic sounds of the farm including a blacksmith forging metal, woodworkers using hand tools to carve wood, children playing period games, lumberjacks shaping logs for buildings, and ranchers cracking whips to drive animals. These historic sounds are documented, along with sounds of the 21st century, including automobile traffic from nearby roadways, aircraft overflights, and various modern machines used in the park to provide a detailed analysis of what a typical rural southern farm soundscape may have sounded like over 100 years ago.

Soundscape analysis of a neonatal intensive care unit (NICU) facility.

A soundscape study was made of an existing NICU facility in a major urban hospital to document the nature and magnitude of sounds experienced by newborn infants in this environment. Focus group discussions were held with hospital administrators, NICU staff, design team members, and families of patients to determine the types of sounds that are heard in normal opera‐tion of the NICU. Long‐term average sound level measurements of general sounds in the NICU were made for several work shifts. Short‐term acoustical measurements of specific acoustic events were also made to obtain octave band sound level data for each of the activities, medical equipment sounds, and building infrastructure sounds that comprise the soundscape of the unit. Audio and video recordings of the specific acoustical events that comprise the soundscape of the NICU were also made. The acoustical measurements and soundscape analysis are used to evaluate proposed acoustical design criteria for NICU facilities compared to nonacoustic health ...

Case study of soundscape assessment and design methods

A case study of the soundscape assessment and design process for an urban design intervention in a medium‐sized city was conducted as an investigation of acoustical assessment and design methods. A series of long‐term acoustical measurements of average sound levels in the community as well as more detailed measurements and aural recordings of specific acoustic events that comprised the ambient sounds were mapped for the community. Measurements included overall A‐weighted and octave band sound levels and calibrated audio recordings. Sound walks were conducted at various times of day to understand the dynamics of the acoustical environment and to identify issues. Focus group discussions among stakeholders and team members developed the long‐term plans for the community and determined appropriate architectural and acoustical design criteria for the project. The acoustical data were used as the basis for determining design strategies for the urban interventions including reducing, buffering, and mitigating undesirable existing sounds, preserving and enhancing desirable existing sounds, and designing new soundscape elements to enhance the comprehensive plan for the community. The results of the study included an assessment of the acoustical analysis methods and soundscape design strategies for the project.

Rotorcraft noise model

The rotorcraft noise model (RNM) is a multiplatform computer program being developed for NASA-Langley Research Center which calculates sound levels at receiver positions on the ground from helicopter and tiltrotor operations. RNM calculates levels at positions on a uniform grid or a specific defined locations. The basic computational model written in FORTRAN calculates maximum A-weighted sound level, sound exposure level (overall, C- and A-weighted), and effective perceived noise level (EPNL). Contained within the program are sound propagation and EPNL algorithms that are the same as, or equivalent to, corresponding algorithms in NASA’s Aircraft Noise Prediction Program (ANOPP). Acoustic properties of the noise source are defined by a set of sound-pressure noise spheres. One set of noise spheres provides broadband data in the form of one-third octave band sound-pressure levels. The other set of noise spheres provides narrow-band data in the form of pure-tone sound-pressure levels and phase. RNM outputs a file that is input to NMPLOT, a noise contouring/smoothing program used by the Department of Defense (DOD) and other government agencies. This paper will describe the basic element of the noise model and compare the noise models prediction with XV-15 noise data collected by NASA-Langley.

A Simplified Method for Field Measurement of Airborne Sound and Impact Sound Insulation in Buildings

A simplified method is investigated to be developed for use by building control inspectors or persons undertaking a similar role to allow a fast and simple check to be carried out on both air-borne and impact sound insulation between rooms. This paper proposes a short test method, in which a standard impact noise source is employed as a simplified source and one third octave band sound level measurement is simplified by A-weighting.

The use of a one‐parameter model to characterize the acoustical properties of asphalt

Following a suggestion by Delany and Bazley [J. Sound Vib. 16, 315–322 (1971)], a single parameter (flow resistivity) fibrous material model has frequently been used to model the acoustical properties of outdoor surfaces. Embleton et al.[J. Acoust. Soc. Am. 74, 1239–1244 (1983)] have shown that an effective flow resistivity for an outdoor surface may be inferred by matching measured and predicted excess attenuations. In this paper, our experience in using such an approach to characterize the acoustical properties of asphalt surfaces will be described. A point source placed directly on the asphalt surface has been used to generate a broadband noise signal. A microphone placed directly on the surface was used to measure 1/3‐octave band sound levels aa a function of frequency (1–20 kHz) and distance from the source (0.1–12.8 m). The flow resistivity of the surface was estimated by comparing theoretical and measured level differences between 0.1 m and the other measurement locations. It was found that it is p...

Outdoor sound level variations due to fluctuating meteorological parameters

Simultaneous measurements of meteorological parameters and octave-band sound levels from a point source, over finite impedance ground, have been carried out. A ray-tracing model was used to predict sound levels. A 5-min measurement period was divided into 10-s intervals, and the effect of the meteorological fluctuations on the measured and predicted sound levels was studied. The meteorological fluctuations were rather large due to the lapse conditions. The results with the ray-tracing model were more sensitive to meteorological variations than was indicated by the measurements. Averages of the predicted sound levels, based on the 10-s intervals, were compared with those predicted from average meteorological conditions, as well as with average measured sound levels. The first of these ray-tracing results was in better agreement with the measurements. It seems that during periods with large meteorological fluctuations, the predicted sound level based on averages can be quite in error. It was also concluded that meteorological fluctuations on a longer time-scale can give similar results to the small-scale turbulence effect, causing decoherence of sound rays.

Über die akustischen probleme der kühltürme

The acoustic problems of cooling towers The paper surveys the different sources of noise in the cooling towers of air conditioning plants, particularly those of fans and water. The empirical formulas for noise evaluation of cooling towers, with axial and centrifugal fans, are given together with a numerical example of total sound power and octave band sound level calculations for a 180-ton refrigeration tower made from three equal units.

A Vehicle for Use as an Audiology Unit

Reliable measurement of hearing by audiometry requires quiet surroundings for which suggested criteria exist. When field studies of hearing are carried out it is frequently most practicable to use a vehicle in which these desired sound levels are obtained. It was decided to incorporate in the design of this vehicle a consulting room and a waiting room so that the patient could adjust to the surroundings for what is essentially a psychological test. Ventilation is effected by input and extractor fans. As a basis for the acoustic design the sound levels in typical situations where the van was to be used were determined. From these it is possible to estimate the attenuation required. The walls and roof of the vehicle are of solid construction with a surface density of 5 lb./sq. ft., and the floor has a surface density of 6 lb./sq. ft. A commercially made booth is suspended on resilient mountings inside the consulting room. The total weight of all the equipment and the sound proofing is in the region of 2 to 3 tons. After construction the sound attenuation of the vehicle was measured in nearly uniform sound fields, provided by a power station and jet engines. Measurements were made simultaneously outside the vehicle, in the consulting room, and inside the booth. The readings were taken in ⅓ octave bands with a calibrated condenser microphone and audio-frequency spectrometer. The results show that the attenuation of the vehicle shell closely follows the predicted value for 5 lb./sq. ft. Subtraction of the overall attenuation from the octave band sound levels in typical factory yards gave a measure of the sound levels to be expected within the booth under field conditions. These showed that the vehicle should be suitable for audiometric measurements of frequencies above 100 cycles per second. To get an accurate value of the attenuation of the booth, which is not symmetrically placed in the consulting room, a source giving a uniform field in the horizontal plane was placed inside the booth and sound level measurements made there and in the consulting room.

Subjective Noise Ratings in Air Force Base Offices

Questionnaires were submitted to 200 Air Force base personnel located in executive, engineering, and shop foremen offices. The questionnaires asked for ratings of the noise conditions, effects of noise on telephone usage and conversation, sources of interfering noises, nature of the job and the activity most affected by the noise. Octave band sound levels and time variation patterns were measured over a period of two weeks for correlation with the subjective information. The results are compared to previously published data [Leo Beranek, Acoustics (McGraw-Hill Book Company, Inc., New York, 1954), pp. 423–425]. [This work was supported by the U. S. Air Force.]