Octave Band Noise Levels Research Articles

Noise Exposure and Hearing Loss among Workers at a Hammer Forge Company.

The National Institute for Occupational Safety and Health (NIOSH) evaluated continuous and impact noise exposures and hearing loss among workers at a hammer forge company. Full-shift personal noise exposure measurements were collected on forge workers across 15 different job titles; impact noise characteristics and one-third octave band noise levels were assessed at the forge hammers; and 4,750 historic audiometric test records for 483 workers were evaluated for hearing loss trends. Nearly all workers' noise exposures exceeded regulatory and/or recommended exposure limits. Workers working in jobs at or near the hammers had full-shift time-weighted average noise exposures above 100 decibels, A-weighted. Impact noise at the hammers reached up to 148 decibels. Analysis of audiometric test records showed that 82% of workers had experienced a significant threshold shift, as defined by NIOSH, and 63% had experienced a standard threshold shift, as defined by the Occupational Safety and Health Administration (OSHA). All workers with an OSHA standard threshold shift had a preceding NIOSH significant threshold shift which occurred, on average, about 7 years prior. This evaluation highlights forge workers' exposures to high levels of noise, including impact noise, and how their hearing worsened with age and length of employment.

Measuring Sound at a Cold-Water Coral Reef to Assess the Impact of COVID-19 on Noise Pollution

This study compares the noise levels at the cold-water coral Tisler reef, before and after the closure of the border between Norway and Sweden, which occurred as a direct result of the COVID-19 pandemic. The Tisler reef is a marine protected area located under a ferry “highway” that connects Norway and Sweden. Cold-water coral reefs are recognised as being important hotspots of both biodiversity and biomass, they function as breeding and nursing grounds for commercially important fish and are essential in providing ecosystem functions. Whilst studies have shown that fishery, ocean warming, and acidification threaten them, the effects of noise pollution on cold-water coral reefs remains unstudied. To study the severity of noise pollution at the Tisler reef, a long-term acoustic recorder was deployed from 29 January 2020 until 26 May 2020. From 15 March COVID-19 lockdown measures stopped passenger vessel traffic between Norway and Sweden. This study found that the overall noise levels were significantly lower after border closure, due to reduced ferry traffic, wind speeds, and sea level height. When comparing the median hourly noise levels of before vs. after border closure, this study measured a significant reduction in the 63–125 Hz 1/3 octave band noise levels of 8.94 ± 0.88 (MAD) dB during the day (07:00:00–19:59:59) and 1.94 ± 0.11 (MAD) dB during the night (20:00:00–06:59:59). Since there was no ferry traffic during the night, the drop in noise levels at night was likely driven by seasonal changes, i.e., the reduction in wind speed and sea level height when transitioning from winter to spring. Taking into account this seasonal effect, it can be deduced that the COVID-19 border closure reduced the noise levels in the 63–125 Hz 1/3 octave bands at the Tisler reef by 7.0 ± 0.99 (MAD) dB during the day. While the contribution of, and changes in biological, weather-related and geophysical sound sources remain to be assessed in more detail, understanding the extent of anthropogenic noise pollution at the Tisler cold-water coral reef is critical to guide effective management to ensure the long-term health and conservation of its ecosystem functions.

Local acoustic habitat relative to hearing sensitivities in beluga whales (Delphinapterus leucas)

Background noise can have a substantial effect on communication signals, however far less is known about how natural soundscapes may influence hearing sensitivity. Here we compare the audiograms of 26 wild beluga whales measured in their natural environment to a series of ecoacoustic measurements within a primary portion of their Bristol Bay summer habitat, the Nushagak Estuary in Bristol Bay, AK, USA. Environmental acoustic measurements were made during 2012 and 2016 using two different methods: a moored recorder and drifter buoys. Environmental noise curves varied substantially. Drifter recordings from the middle of Nushgak Estuary had the highest spectrum levels during ebb tides with acoustic energy from sediment transport extending well into higher frequencies (ca. 60 kHz), likely due to rapidly moving tidal flow and shifting sediment in that location. Drifter recordings near the estuary mouth and shallow tidal flats were lower amplitude. Noise levels generally varied during drifts (in one case up to ca. 6 dB) reflecting acoustic cues available to the local belugas. The moored recorder showed a substantially different spectral profile, especially at lower frequencies, perhaps due to its attachment to a pier piling and subsequent pier noise. Hearing sensitivity varied by individual and thresholds often fell above 1/3 octave-band noise levels, but not overall noise spectral density. Audiograms of the most sensitive animals closely paralleled the lowest ambient noise power spectral density curves, suggesting that an animal’s auditory dynamic range may extend to include its habitat’s quietest conditions. These data suggest a cautious approach is necessary when estimating the sound-sensitivity of odontocetes found in quiet environments as they may have sensitive auditory abilities that allow for hearing within the lowest noise-level conditions. Further, lower level ambient noise conditions could provide a conservative estimate of the maximal sensitivity of some cetacean populations within specific environments.

Spatial and Temporal Variation in the Acoustic Habitat of Bottlenose Dolphins (Tursiops aduncus) within a Highly Urbanized Estuary

There is growing awareness of underwater noise in a variety of marine habitats, and how such noise may adversely affect marine species. This is of particular concern for acoustically-specialised species, such as dolphins. In order to ascertain the potential impacts of anthropogenic noise on these animals, baseline information is required for defining the soundscape of dolphin habitats. The Swan-Canning River system in Western Australia flows through the city of Perth, and experiences numerous anthropogenic activities. Despite this, the river system is home to a community of Indo-Pacific bottlenose dolphins (Tursiops aduncus). To provide a baseline soundscape description of dolphin habitat, over 11,600 h of acoustic data were analysed from five sites within the Swan River (from Fremantle Inner Harbour to 20 km upstream) across an eight-year period. Multiple sound sources were recorded at these sites, including: snapping shrimp; fishes; dolphins; pile-driving; bridge and road traffic; and vessel traffic. The two most prevalent sound sources, vessel traffic and snapping shrimp, likely have very different effects on dolphin communication with the former expected to be more disruptive. Sites were characteristic in their prominent sound sources, showing clear among-site variations, with some sites being ‘noisier’ than others based on broadband noise levels, octave-band noise levels, and power spectrum density percentiles. Perth Waters had the highest broadband noise (10 Hz – 11 kHz; mean 113 dB re 1 µPa rms), whilst Heirisson Island was quietest (mean 105 dB re 1 µPa rms). Generalised estimating equations identified variation in broadband noise levels within sites at a fine temporal scale, although sites differed in the significance of temporal variables. At Mosman Bay, a long-term dataset spanning eight years highlighted inter-annual variation in broadband noise levels, but no overall upwards or downwards trend over time. Acoustic habitats of the Swan River displayed significant variations at a variety of temporal and spatial scales, throughout areas frequented by the local dolphin community. Such variations should be quantified when assessing dolphin acoustic habitat as they may provide significant clues to dolphin behaviour.

Interior Noise Characteristics in Japanese, Korean and Chinese Subways

The aim of this study was to clarify the characteristics of interior noise in Japanese, Korean, and Chinese subways. The octave-band noise levels, A-weighted equivalent continuous sound pressure level (<TEX>$L_{Aeq}$</TEX>) and parameters extracted from interaural cross-correlation/autocorrelation functions (ACF/IACFs) were analyzed to evaluate the noise inside running train cars quantitatively and qualitatively. The average <TEX>$L_{Aeq}$</TEX> was 72-83 dBA. The IACF/ACF parameters of the noise showed variations in their values, suggesting they are affected by the characteristics of the trains running, wheel-rail interaction, and cross-section of the tunnels.

Pavement characteristics affecting the frequency content of tire/pavement noise

Tire/pavement noise is a major contributor to traffic noise at highway speeds. Annoyance is more closely related to frequency content than to overall A-weighted noise levels, therefore spectral content analysis of tire/pavement noise is an important consideration. A study conducted in California measured the noise levels of different mix types and the pavement characteristics affecting noise levels as determined by on-board sound intensity (AASHTO TP 76-08). Data was collected on dense-graded asphalt concrete mixes (DGAC), conventional open-graded mixes (OGAC), open-graded rubberized asphalt concrete mixes (RAC-O), and gap-graded rubberized asphalt concrete mixes (RAC-G) with ages less than 8 years old. This paper evaluates the effects of pavement characteristics including the air-void content, gradation properties, rubber inclusion, roughness, texture, pavement surface condition, and age on one-third octave band noise levels. This research confirmed that macrotexture and IRI, which are associated with the impact and shock mechanisms, increase the noise levels at lower frequencies. Higher air-void content, associated with the air pumping mechanism, reduces the noise levels at higher frequencies.

Further acoustical analysis of infant/toddler rooms in daycare centers

At the last ASA meeting, preliminary data was shared on the background noise in daycare centers. At this meeting, further research in the acoustical analysis of infant/toddler rooms in seven daycare centers will be discussed in relation to speech communication. Information concerning the collection and analysis of ambient noise, signal-to-noise ratios (SNRs), reverberation times (RT), and early decay time (EDT) will be shared. Comparisons will be made between the measurements and data collection techniques of ambient noise from dosimeters, sound level meters, and other long-term data acquisition techniques. Comparisons of the overall and octave band RTs and EDTs from each of the rooms in the study will be shown. Finally, the calculation of SNRs will be shown for both steady-state and dynamic signals. The steady-state SNR uses several different speech spectra compared to the occupied 1/3-octave band noise levels. The dynamic SNRs are calculated using microphones placed at both the caregiver and the infant or toddler. [Work supported by PHS/NIH (1-R01-HD31540-01A2) Otitis Media, Behavior and Attention in Daycare.]

Sound levels daring operation of magnetic resonance imaging systems

The sound or noise levels at the patient position in the bore of several different magnetic resonance imaging (MRI) systems were measured. The measurements were conducted with the microphone/preamplifier component connected to the sound-level meter (SLM) with an extension cable so that the SLM was remote from the MRI scan room. Preliminary tests and analyses were conducted to ascertain that the microphone/preamp functioned normally in the strong magnetic field and rf environment. Subsequently, A-weighted, flat-weighted, and octave band noise levels were measured in the MRI system bore areas during a variety of image scanning sequences. The noise levels were in the range 75–95 dB A-wt., and 85–105 dB flat-wt. Greater noise levels tended to be correlated with greater magnetic field strengths and with more rapid and detailed image scanning sequences.

Application of multiple regression method to prediction of octave band noise levels in ship accommodation spaces

Application of multiple regression method to prediction of octave band noise levels in ship accommodation spaces

Application of multiple regression method to prediction of A-weighted noise levels in ship accommodation spaces

This article discusses the final stage of an investigation leading to a method for predicting octave band noise levels. The method is based on statistical multiple regression theory. Results from using this method correspond with measurements taken. Accuracy is comparable with that of other equivalent methods for predicting octave band noise levels.

A psychophysical evaluation of the dependence of hearing protector attenuation on noise level.

The attenuation characteristics of ten commercially available hearing protectors (five muffs and five plugs) were examined for 1/3-octave bands of noise centered at 1000, 2000, 3150, 4000, and 6300 Hz in ten normal-hearing young adults utilizing four psychophysical procedures. One of these procedures, the real-ear attenuation at threshold procedure described in the American standard for the evaluation of hearing protectors, is designed for use at 1/3-octave band noise levels below approximately 50 dB SPL. Three real-ear psychophysical procedures were also developed and evaluated. These procedures were: (1) a reaction-time paradigm; (2) a loudness magnitude-estimation procedure; and (3) a masked bone-conduction threshold technique. Each procedure was designed to evaluate protectors for 1/3-octave bands of noise having levels ranging from approximately 50 to 90 dB SPL. Mean data indicated that: (1) attenuation was linear over the range investigated, although some exceptions to this generalization were apparent; (2) attenuation estimates derived with the reaction-time and magnitude-estimation paradigms were typically less than those obtained with the other two methods; and (3) all attenuation estimates, regardless of procedure, were less than manufacturer's specifications for the majority of the protectors. Implications for existing standards are discussed.

A double-wall noise control enclosure for an impulsive sound source.

Abstract The design of a group of double-wall noise control enclosures on the upper floor of an existing building is described and some noise reduction measurements are reported. A design objective for these enclosures was to achieve more effective noise reduction than that provided by existing heavy, on-grade, double-wall, reverberant enclosures, but with reduced weight. This objective was achieved by a combination of a light weight inner skin, a moderately large air space, a masonry exterior, isolation of the inner room floor slab, and the use of sound absorbing materials. Other noise control measures included sound retarding doors and windows, mufflers in the air supply and return passages, and flexible service connections to the rooms. Peak and octave band noise levels taken inside and outside the old and new enclosures are reported.

A Double Wall Noise Control Enclosure for an Impulsive Sound Source

The design of a group of double wall noise control enclosures on the upper floor of an existing building is described and some noise reduction measurements are reported. A design objective for these enclosures was to achieve more effective noise reduction than that provided by existing heavy, on grade, double wall, reverberant enclosures, but with reduced weight. This objective was achieved by a combination of a lightweight inner skin, a moderately large air space, a masonry exterior, isolation of the inner room floor slab, and the use of sound absorbing materials. Other noise control measures included sound retarding doors and windows, mufflers in the air supply and return passages, and flexible service connections to the rooms. Peak and octave band noise levels taken inside and outside the old and new enclosures are reported.

Acoustic Factors in the Design of Noise-Reducing Telephone Booths

Acoustically treated, doorless telephone booths can increase the effectiveness of telephone communication in noisy environments even though practical size and open area requirements limit the amount of noise reduction which can be achieved. The principal factors determining the noise reduction of an acoustically treated booth (where the noise reduction is considered as the decibel difference in octave band noise levels measured outside and inside the booth) have been investigated by use of full size and 13 model booths. The principal parameters affecting the reduction of an acoustically treated telephone booth were found to be (1) the sound absorption coefficients of the wall surfaces as function of frequency; (2) the ratio of open area to the wall area of the phone booth; (3) the transmission loss of the walls of the phone booth; and (4) the size and shape of the booth. The investigation resulted in a new triangular design of booth which is fully as effective acoustically as the rectangular booths, yet has added practical advantages.