Octave Band Sound Pressure Levels Research Articles

Large aperture microphone array measurement at operating airport for sound source model creation of J-FRAIN

In 2022, authors conducted microphone array measurements at an operating airport to create sound source models for commercial aircraft based on the noise prediction framework J-FRAIN. A similar measurement was also performed by our colleagues in 2019, but it was a trial to establish the concept of the framework and was done using a microphone array in which the number of microphones was reduced to about half. In order to improve the accuracy of the sound source models, the microphone array with a 30-meter diameter consisting of 195 microphones mounted on the ground was used in 2022. Recording-based simultaneous noise measurement using sound level meters was also performed around the airport to validate prediction results in terms of time histories of 1/3 octave band sound pressure levels. This paper describes an overview of the microphone array measurements conducted in 2022 and a case study of noise prediction around the airport using sound source models created from the data of microphone array measurements conducted in 2022. Predicted results are compared with 1/3 octave band data measured using sound level meters mounted at a height of 4 m above the ground at sites of noise monitoring stations around the airport.

A year of background sound measurements in suburbia

An internal research project was undertaken to measure the background sound levels at one location with the same equipment for a full year. A suitable location was identified to allow the equipment to stay in the same place and available to refresh data memory cards and battery power. The sound monitoring was done from October 2020 through November of 2021. The site selected was a typical suburban residential property near a secondary road, but far from other influencing sources of sound like highways and industry. The data set is over 9,000 hourly samples of A-weighted sound levels. For each hour the L99, L90, L50, L10, L01 and LEQ were recorded and evaluated for this study. This paper addresses the compilation of the year worth of A-weighted sound levels. The data set also includes one-third octave band sound pressure levels, but those data have not been considered in this evaluation. The noted sound metrics have been evaluated by month, day of the week and hour. The paper also evaluates the selection of the lowest background sound level that is used in many noise ordinances, including the author's home state of Massachusetts.

Cooperative-hydrophone-based underwater soundscape monitoring in a bustling harbor enhanced by coral ecosystem

Anthropogenic underwater noise is an emerging pollutant, urging a focus on studying the spatial and temporal dynamics of underwater soundscapes for effective environmental protection. This study centers on a bustling harbor enriched by coral ecosystems, employing 5–8 spatially distributed bottom-mounted passive acoustic monitoring (PAM) nodes strategically placed at locations of interest with diverse natural conditions and ship traffic intensities. Focused on the intricate interplay between anthropogenic and natural contributors, including shipping traffic and coral ecosystems, one-third octave band sound pressure levels SPLs were calculated and analyzed at different frequencies, revealing significant variations in levels across different times and locations. Diurnal variations in ambient noise levels highlight the complex relationship between human activities and marine ecosystems. Higher and more variable SPLs, primarily related to shipping traffic, were recorded during the daytime, while lower SPLs, accompanied by increased fish sounds, were observed at night. The collaborative deployment of multiple hydrophones enables an estimation of noise source direction, and multi-hydrophone based principal component analysis (PCA) for dimensionality reduction and subsequent clustering methods were used for noise source classification. This study significantly contributes to the field of underwater noise monitoring, offering a holistic perspective on busy harbor environments.

First basin scale spatial–temporal characterization of underwater sound in the Mediterranean Sea

Anthropogenic underwater noise is an emergent pollutant. Despite several worldwide monitoring programs, only few data are available for the Mediterranean Sea, one of the global biodiversity hotspots. The results of the first continuous acoustic programme run at a transnational basin scale in the Mediterranean Sea are here presented. Recordings were done from March 2020 to June 2021, including the COVID-19 lockdown, at nine stations in the Northern Adriatic Sea. Spatial–temporal variations of the underwater sound are described, having one third octave band sound pressure levels (SPLs) from 10 Hz to 20 kHz as metrics. Higher and more variable SPLs, mainly related to vessel traffic, were found close to harbours, whereas Natura 2000 stations experienced lower SPLs. Lower values were recorded during the lockdown in five stations. Median yearly SPLs ranged between 64 and 95 as well as 70 and 100 dB re 1 µPa for 63 and 125 Hz bands, respectively. These values are comparable with those previously found in busy shallow EU basins but higher levels are expected during a business-as-usual period. This is a baseline assessment for a highly impacted and environmental valuable area, that needs to be managed in a new sustainable blue growth strategy.

Evaluation of the uniformity of sound-masking systems in an open-plan office

Many open-plan offices adopt an electronic sound masking system in order to reduce distraction from background noises, primarily intruding speech. Sound masking systems should uniformly generate a masking sound over the entire office area to homogenize the speech privacy whilst minimising occupant perception of the masking sound. This study evaluates the spatial uniformity of the masking sound field in an example open-plan office, where the masking system was set up to represent supposedly optimal installation conditions; 1-speaker zones, individually-calibration of each zone to match the specified curve precisely, and smaller zones than typically specified. Sound level measurements performed as per ASTM E1573-18 were made at each workstation, as well as every 0.6 m across the office, for a total of 117 measurements. Measurement results show that tolerance of ± 0.5 dB for the overall A-weighted level is only achievable at 61% of measurement locations, whilst ± 1 dB is achievable at 99% of locations. For one-third-octave band sound pressure levels between 250 Hz and 4 kHz, ± 2 dB is achieved only 55% of the time, and tolerance of ± 3.5 dB is required to achieve 95% compliance with the specified curve. By using calibrated computer simulations, the study also examined parameters that can influence spatial uniformity in open-plan offices. It was found that the number of sound masking loudspeakers, partition height, and the scattering and absorption coefficient of the ceiling all affect the uniformity of the masking sound. Speech intelligibility was assessed by calculating the Articulation Index (AI) to determine an acceptable tolerance for masking sound variation. Increasing the number of loudspeakers was the most effective way to improve the uniformity of the masking sound. The AI results suggest ± 2 dB, when including octave band sound pressure levels, is a minimum required tolerance for a sound masking sound field in an open office to provide AI values within ± 0.1 of the targeted value across the office area.

Design and application of sound barrier for substation noise control

After measuring the noise of transformers, substation boundary and noise-sensitive area of a 110 kV substation, it’s known that the noise at substation boundary contains transformer noise component via analyzing the 1/3-octave band spectrums. The octave band sound pressure level on the roof of the east residential building derived from the transformer is obtained by sound field prediction of SoundPLAN. Moreover, the NR-40 curve is used to evaluate the octave band sound pressure level to calculate the theoretical noise reduction of the east residential building. Considering the direct propagation and another propagation path undergoing reflection, a sound barrier that composed of sound insulation board with a significant sound insulation effect is designed for the frequency band below 1000 Hz. After completely installing the sound barrier, the noise level at measuring point 16 at night is reduced from 55.9 dB(A) to 46.7 dB(A), with noise reduction of 9.2 dB(A); while it is reduced from 56.3 dB(A) to 44.5 dB(A) at measuring point 21, with noise reduction of 11.8 dB(A).

Frequency weighting to evaluate the feeling of pressure and/or vibration caused by low-frequency noise: Re-analysis of an existing study

Low-frequency noise may create specific perceptions, which might cause various health effects. The present study aimed to identify exposure–response relationships between low-frequency noise and perceptions by re-analysing an experimental study. We investigated the predominant perceptions of ‘feeling bothered’ and ‘feeling of pressure and/or vibration’ using multivariate logistic regression analysis. A significant interaction between 1/3 octave-band sound pressure level and frequency was indicated for ‘feeling bothered’ but not ‘feeling of pressure and/or vibration’, suggesting that the ‘feeling of pressure and/or vibration’ does not originate in cochlear. A mathematical model indicating resonance at approximately 50 Hz fitted the results well. A frequency weighting derived from the mathematical model could be applied to broad-band low-frequency noise to evaluate the perception and health effects. However, further investigations on the weighting for the perception are necessary because the results were obtained only from the existing study.

청감실험을 통한 실내에서의 저주파 소음의 단일수치평가량 제안

In this study, new single number quantities (SNQs) based on 1/3 octave band sound pressure levels and low-frequency noise criteria were proposed to evaluate low-frequency noise in indoor spaces. The suitability of the proposed SNQs (D<SUB>max</SUB> and D<SUB>sum</SUB>) was assessed through correlation analysis with other existing SNQs (L<SUB>Ceq</SUB> and L<SUB>Zeq</SUB>) and confirmed by an auditory experiment conducted for construction and air-conditioner outdoor unit noise to be infiltrated from outdoor to indoor spaces. The result showed that the proposed SNQs were highly correlated with the existing SNQs in the range of 0.81 to 0.95. The auditory experiment also revealed that the proposed SNQs had a high correlation with subjective annoyance in the range of 0.81 and 0.89 out of the total range of presentation levels, and a similar correlation with existing SNQs for each presentation level. The proposed SNQs will be able to identify the major frequency bands in terms of annoyance and help assess and establish countermeasures at the site of the low-frequency noise.

Spatial and Temporal Variability of Ambient Underwater Sound in the Baltic Sea

During last decades, anthropogenic underwater sound and its chronic impact on marine species have been recognised as an environmental protection challenge. At the same time, studies on the spatial and temporal variability of ambient sound, and how it is affected by biotic, abiotic and anthropogenic factors are lacking. This paper presents analysis of a large-scale and long-term underwater sound monitoring in the Baltic Sea. Throughout the year 2014, sound was monitored in 36 Baltic Sea locations. Selected locations covered different natural conditions and ship traffic intensities. The 63 Hz, 125 Hz and 2 kHz one-third octave band sound pressure levels were calculated and analysed. The levels varied significantly from one monitoring location to another. The annual median sound pressure level of the quietest and the loudest location differed almost 50 dB in the 63 Hz one-third octave band. Largest difference in the monthly medians was 15 dB in 63 Hz one-third octave band. The same monitoring locations annual estimated probability density functions for two yearly periods show strong similarity. The data variability grows as the averaging time period is reduced. Maritime traffic elevates the ambient sound levels in many areas of the Baltic Sea during extensive time periods.

Out-of-Booth Testing with Noise-canceling Earphones

Out-of-Booth Testing with Noise-canceling Earphones

Operational noise associated with underwater sound emitting vessels and potential effect of oceanographic conditions: a Dublin Bay port area study

This study presents analysis of acoustic data of underwater sound emitting vessels (USEV) recorded during operation in the Dublin Bay port area. Investigations were carried out to assess the magnitudes of these underwater sounds, and also the potential effect of changes in tidal states on these sound signals and their propagation. Power spectral densities (PSD) and 1/3 octave band sound pressure levels (SPL) were computed for frequencies between 50–500 and 50–1000 Hz, respectively. During the presence of these vessels in the study site, broadband SPL values for a range of frequency components were calculated to be between 94 and 121 dB (re 1 µPa) at a distance of 200 m from the vessels. These values decreased by 5–21 dB during their absence. The strongest sound level recorded at this site was during the departure of vessels from the dock at 200 m from the recording system. The SPL value calculated during this operational period at 315 Hz frequency was 121 dB re 1 µPa2/Hz. Associated components’ spectral of the vessels were identified, and the effect of difference in heights of tidal ranges (Neap/Spring) on this site was investigated.

Test and rating method comparison between Japan and the U.S. for airborne sound insulation in buildings

The Japanese test methods for laboratory measurement of airborne sound transmission loss for building partitions are basically the same as the American test methods. However, the two countries’ field test methods for airborne sound insulation in buildings differ. The octave band sound pressure level difference between two rooms is the most significant value for the field evaluation of sound insulation in Japan, whereas the apparent transmission loss for a partition installed in a building is the most popular value for the field evaluation of sound insulation in the US. Why is the octave band sound pressure level difference popular in Japan? It is the basic way of thinking in Japan that an acoustical engineer should take responsibility for the total spatial sound insulation performance, including sound absorption and flanking transmission from the design stage to completion and the field test and evaluation method as the completion inspection should be simple. If the insulation performance does not meet th...

Development of hearing protection device calculators for the F-35A and F-35B tactical aircraft

Simple spreadsheet-based near field noise prediction tools for the F-35A (conventional takeoff and landing) and F-35B (short takeoff and vertical landing) aircraft have been developed recently. Near field noise predictions are based on empirical data collected during static engine runs conducted at Edwards AFB, and during hover/vertical landing operations at MCAS Yuma in September, 2013. The tools are programmed to calculate near field one-third octave band sound pressure levels as a function of engine power setting and listener location. The calculated near field levels can be used to determine the Total Daily Exposure (TDE) of personnel required to work in the vicinity of powered aircraft. Alternatively, the calculators can be used to determine the amount of hearing protection required so that the personnel TDEs remain below 1.0. The calculators are adjustable so that they can be employed for differing domestic and international noise exposure regulations. [Work supported by the Air Force Research Laboratory and Ball Aerospace.]

Effects of Gas Production on Acoustic Radiation Characteristics of Underwater Pyrotechnic Combustion

In order to understand the effects of gaseous production on the acoustic radiation characteristics of underwater pyrotechnic combustion, the pyrotechnic combustion pressure-time curves are plotted using a closed bomb and then maximum pressure is used to calculate the quantity of gaseous products. The results show that among the four pyrotechnic compositions with different gas productions, overall sound pressure level (OASPL) and 1/3 octave band sound pressure level (SPL) in composition #4 which has the highest nozzle gas flow, shortest period of bubble formation and largest maximum bubble diameter, reached 165.1 dB and 163 dB respectively, which were 6 dB and 10 dB higher than the corresponding minimum values. During underwater pyrotechnic combustion, bubbles were formed at the nozzle of the combustion device and thus generated low-frequency noise. The increased gas production resulted in a shorter bubble formation period, a larger number of bubbles, and larger bubble diameter, which destabilize the fluid during bubble formation, improve the prone of bubbles to coalescence and breakup, and increase the sound pressure level.

Acoustics research of propulsion systems

The liftoff phase induces high acoustic loading over a broad frequency range for a launch vehicle. These external acoustic environments are used in the prediction of the internal vibration responses of the vehicle and components. Present liftoff vehicle acoustic environment prediction methods utilize stationary data from previously conducted hold-down tests to generate 1/3 octave band Sound Pressure Level (SPL) spectra. In an effort to update the accuracy and quality of liftoff acoustic loading predictions, non-stationary flight data from the Ares I-X were processed in PC-Signal in two flight phases: simulated hold-down and liftoff. In conjunction, the Prediction of Acoustic Vehicle Environments (PAVE) program was developed in MATLAB to allow for efficient predictions of sound pressure levels (SPLs) as a function of station number along the vehicle using semi-empirical methods. This consisted of generating the Dimensionless Spectrum Function (DSF) and Dimensionless Source Location (DSL) curves from the Ares I-X flight data. These are then used in the MATLAB program to generate the 1/3 octave band SPL spectra. Concluding results show major differences in SPLs between the hold-down test data and the processed Ares I-X flight data making the Ares I-X flight data more practical for future vehicle acoustic environment predictions.

Introduction of sound material in living environment 2004 (SMILE 2004): A sound source database for educational and practical purposes

Sound sources are used in various settings of education, research, and business that are related to architectural acoustics. Especially in educational scenarios, they are very effective for students to learn theories together with the experience of listening to actual sounds related to them. Sound Material In Living Environment (SMILE 2004), a sound source database published in 2004 in DVD form (Japanese only), is the culmination of our project. SMILE 2004 is intended as a collection of sample sounds for use in lectures on architectural acoustics at universities or industrial high schools. In addition, it is useful for measurements or demonstrations for academic or practical purposes. The database contains 913 digital sound files of real sounds and impulse responses, which cover the study fields of acoustics, noise control, and soundscapes. Each sound is accompanied by such information as the 1/1 octave band sound pressure levels and a brief explanation and photographs of the situation in which the sound was recorded. In addition, sample presentations for lectures and practical demonstrations are attached as examples of the use of this database for educational and practical purposes. Details of all the above features will be introduced in a demonstration.

Room noise criteria—A new approach at low frequencies

ANSI S12.2-1995, ‘‘Criteria for Evaluating Room Noise,’’ permits two different sets of criterion curves for evaluating room noise—room criterion (RC) and balanced noise criterion (NCB)—with little guidance as to the selection. These different procedures can have significant impacts on the cost of designs, especially in the low-frequency regions, since the difference in the criteria is more than 10 dB in the 16- and 31-Hz octave bands at lower levels. The authors suggest there are sufficient data to support a modification to ANSI S12.2, resulting in a single evaluation procedure based on the strengths of each of the two existing procedures. The authors suggest establishing room criterion curves for steady noise without abnormal temporal or spectral characteristics, with correction factors for noises with abnormal features. The suggested criteria for steady noise are the NCB curves based on time-average octave band sound pressure levels, and as a starting point, the correction factors for low-frequency tones and fluctuation differences between the NCB and RC curves. Analyses of currently funded research and re-examination of existing cases can determine the exact correction factors and measurement techniques to quantify these abnormal characteristics. A revised ANSI S12.2 could have basic criterion curves for steady, continuous, and broadband room noises, which could be used for design with correction factors to these basic criterion curves for sounds with abnormal characteristics. [See NOISE-CON Proceedings for full paper.]

Personal Cassette Players (‘Walkman’). Do they Cause Noise-Induced Hearing Loss?

Playing selected types of music on five different personal cassette players (PCPs) and using different gain (volume) settings, A-weighted maximum and equivalent sound pressure levels (SPLs) were measured on KEMAR (Knowles Electronics Manikin for Acoustic Research). The octave band SPLs were measured on KEMAR ear and transformed to field values in order to compare measured values with the Norwegian noise risk criteria. Temporary threshold shifts (TTS) measured in 6 subjects after listening to two different pop music cassettes on one PCP in two separate sessions, are presented. Based upon these studies we conclude that the risk of acquiring permanent noise-induced hearing loss (NIHL) from use of PCP is very small for what we found to be normal listening conditions.

Hearing-damage Risk and Communication Interference in Dental Practice

The use of high-speed air-turbine handpieces, operated at 300,000 to 400,000 revolutions per minute, has led to concern over the possibility of noise-induced hearing loss. Sound levels were measured in clinical settings and in a pre-clinical laboratory for estimation of hearing-damage risk among dentists, and the extent of communication interference. Octave-band sound pressure levels were obtained with use of a Fast-Fourier-Transform analyzer and associated instrumentation. The results of this study indicate that the sound energy contribution of a typical dental practice is about 8% to 12% of the dentist's average 24-hour noise exposure. However, noise levels during dental procedures result in an articulation index of 0.21 to 0.37, corresponding to understanding of about 18% to 48% of nonsense syllables and 52% to 90% of sentences. It appears that hearing-damage risk is slight among dentists using modern equipment. However, further noise control in handpieces is necessary so that error-free communication during dental procedures can be ensured.

Model scale testing of outdoor noise propagation from a power plant

A proposed cogenerating power plant of 70-MW capacity is to be located in an urban setting and will be subject to stringent environmental noise emission criteria. A four-cell forced draft cooling tower is included in the plant design. Computer modeling of cooling tower noise propagation to affected neighboring residences involved significant uncertainties due to the complex shapes of power plant building elements and existing surrounding buildings. Without a finished facility in which to perform full-scale field tests, the next best thing is a scale model test. This paper will discuss the specifics of the 1/20th scale test setup, materials, selection, instrumentation, test execution, some problems and some lessons learned. The results of the test will be given in terms of the differences in octave band sound-pressure levels between an unobstructed free-field value and the modeled in situ value, at several receptor positions. The test enabled the specification of more precise sound attenuating elements for the cooling tower fans and inlets in order to comply with the governing regulations.