High Ambient Noise Research Articles

Performance of a high-frequency acoustic forward-scatter barrier in a dynamic coastal environment

This paper investigates the performance of a high-frequency ‘‘barrier’’ or ‘‘tripwire’’ surveillance system based on forward scattering for shallow water (<20 m depth) choke points, such as harbor entrance. Harbor entrances are usually regions of very high ambient noise and often are reverberation-limited environments, making them challenging for some traditional ASW techniques, i.e., techniques inherited from blue-water ASW. Detecting a target by measuring its forward-scattered field is of interest because sound scattered in the forward direction is generally higher than in the backward direction. We will present a series of proof-of-concept experiments to test the feasibility of an acoustic tripwire based on forward scattering using two vertical source and receive arrays operated over a 135-m range at a center frequency of 15 kHz with about 8 kHz of bandwidth. The signal of interest was the aberration (in space and time) caused by the acoustic forward scattering field of a crossing object (scuba tank, 2-m-long steel cylinder and 1-m-diam steel sphere). Autonomous signal processing techniques based on the spatio-temporal coherence of the signals measured across the vertical receive array were applied to enhance the signal of interest, yielding a usable detection threshold of several dB.

Underwater noise and zones of masking with respect to hopper dredging and manatees in the St. Johns River in Jacksonville, FL

Underwater noise radiating from dredging can effectively obscure or mask biological and other important sounds. This study recorded underwater acoustic characteristics of hopper dredging in the St. Johns River, Jacksonville, FL, to evaluate noise impacts in the waterway with respect to the endangered West Indian manatee. Of particular interest was the extent and range that dredging noise may mask the sounds of approaching commercial and recreational vessels. Vertical hydrophone arrays and a multi-channel PC-based recording system were used to measure dredging noise at various distances. Ambient noise surveys, active propagation of calibrated sources, and controlled boat noise measurements were conducted along the waterway. These data were integrated with behavioral hearing data to estimate zones of masking surrounding dredging. Three discernable noise sources that masked boat noise were (1) cavitation from dredge propellers, (2) draghead vacuuming, and (3) noise from submerged slurry pipelines. Sustained high ambient noise levels from dredging can significantly increase the risk of manatee-boat collisions by masking the sounds of approaching vessels over large radii (up to 2.5 miles). Mitigations suggested include ship quieting, reducing propeller cavitation, insulating or elevating slurry pipelines, and minimizing transects to pump out stations. [Work funded by the City of Jacksonville Waterways Commission.]

Multiple Auditory Steady-State Response Thresholds to Bone-Conduction Stimuli in Young Infants with Normal Hearing

Multiple auditory steady-state responses (ASSRs) probably will be incorporated into the diagnostic test battery for estimating hearing thresholds in young infants in the near future. Limiting this, however, is the fact that there are no published bone-conduction ASSR threshold data for infants with normal or impaired hearing. The objective of this study was to investigate bone-conduction ASSR thresholds in infants from a Neonatal Intensive Care Unit (NICU) and in young infants with normal hearing and to compare these with adult ASSR thresholds. ASSR thresholds to multiple bone-conduction stimuli (carrier frequencies: 500 to 4000 Hz; 77 to 101-Hz modulation rates; amplitude/frequency modulated; single-polarity stimulus) were obtained in two infant groups [N = 29 preterm (32 to 43 wk PCA), tested in NICU; N = 14 postterm (0 to 8 mo), tested in sound booth]. All infants had passed a hearing screening test. ASSR thresholds, amplitudes, and phase delays for preterm and postterm infants were compared with previously collected adult data. Mean (+/-1 SD) ASSR thresholds were 16 (11), 16 (10), 37 (10), and 33 (13) dB HL for the preterm infants and 14 (13), 2 (7), 26 (6), and 22 (8) dB HL for the postterm infants at 500, 1000, 2000, and 4000 Hz, respectively. Both infant groups had significantly better thresholds for 500 and 1000 Hz compared with 2000 and 4000 Hz, in contrast to adults who have similar thresholds across frequency (22, 26, 18, and 18 dB HL). When 500- and 1000-Hz thresholds were pooled, pre- and postterm infants had better low-frequency thresholds than adults. When 2000- and 4000-Hz thresholds were pooled, pre- and postterm infants had poorer thresholds than adults. ASSR amplitudes were significantly larger for low frequencies compared with high frequencies for both infant groups, in contrast to adults, who show little difference across frequency. ASSR phase delays were later for lower frequencies compared with higher frequencies for infants and adults, except for 500 Hz in the preterm group. ASSR phase delays were later for infants compared with adults across frequency. Infant bone-conduction ASSR thresholds are very different from those of adults. Overall, these results indicate that low-frequency bone-conduction thresholds worsen and high-frequency bone-conduction thresholds improve with maturation. Bone-conduction ASSR threshold differences between the postterm infants and adults probably are due to skull maturation. Differences between preterm and older infants may be explained both by skull changes and a masking effect of high ambient noise levels in the NICU (and possibly to other issues due to prematurity).

Voice intelligibility enhancement system

Intelligibility of a human voice projected by a loudspeaker in an environment of high ambient noise is enhanced by processing a voice signal in accordance with the frequency response characteristics of the human hearing system. Intelligibility of the human voice is derived largely from the pattern of frequency distribution of voice sounds, such as formants, as perceived by the human hearing system. Intelligibility of speech in a voice signal is enhanced by filtering and expanding the voice signal with a transfer function that approximates an inverse of equal loudness contours for tones in a frontal sound field for humans of average hearing acuity.

The Effect of Noise in the Emergency Department

Background: It is hypothesized that high ambient noise in the emergency department (ED) adversely affects the ability of the examiner to hear heart and lung sounds. Objective: To determine the ability of various examiners to hear heart tones and lung sounds at the high end of loudness typically found in the ED setting. Methods: The study was divided into two parts. First, sound levels in the ED were measured over various times during the months of January through June 2001, using a sound level monitor. The second part of the study was the determination of the ability to hear heart and lung sounds on a young healthy volunteer using the same Littmann lightweight stethoscope at a predetermined ambient noise level of 90 dB. The results were entered into a database and analyzed using SPSS version 10 (Chicago, IL). Descriptive statistics, analysis of variance, frequencies, and correlation were calculated using this program. Results: Two hundred five sound measurements were taken in the ED during the study period in three locations at various hours. The mean noise level at the nursing station was 57.60 dB, with a minimum of 45.00 dB and a maximum of 70.00 dB. Four of the 104 test subjects (3.8%) were unable to hear the heart tones, and nine of the 104 (8.7%) were unable to hear the lung sounds. Fifty percent (27 of 54) of the test subjects reported diminished lung sounds and eight of 15 (53.3%) reported diminished heart sounds. No significant difference was found between hearing heart sounds and years of experience, age, professional position, and quality of the sound. Significant differences were found between hearing lung sounds and years of experience and professional position, but not with age, gender, and sound quality. Conclusions: This study demonstrated that most of the tested examiners have the ability to hear heart and lung sounds at the extreme of loudness found in one ED.

The Effect of Noise in the Emergency Department

It is hypothesized that high ambient noise in the emergency department (ED) adversely affects the ability of the examiner to hear heart and lung sounds. To determine the ability of various examiners to hear heart tones and lung sounds at the high end of loudness typically found in the ED setting. The study was divided into two parts. First, sound levels in the ED were measured over various times during the months of January through June 2001, using a sound level monitor. The second part of the study was the determination of the ability to hear heart and lung sounds on a young healthy volunteer using the same Littmann lightweight stethoscope at a predetermined ambient noise level of 90 dB. The results were entered into a database and analyzed using SPSS version 10 (Chicago, IL). Descriptive statistics, analysis of variance, frequencies, and correlation were calculated using this program. Two hundred five sound measurements were taken in the ED during the study period in three locations at various hours. The mean noise level at the nursing station was 57.60 dB, with a minimum of 45.00 dB and a maximum of 70.00 dB. Four of the 104 test subjects (3.8%) were unable to hear the heart tones, and nine of the 104 (8.7%) were unable to hear the lung sounds. Fifty percent (27 of 54) of the test subjects reported diminished lung sounds and eight of 15 (53.3%) reported diminished heart sounds. No significant difference was found between hearing heart sounds and years of experience, age, professional position, and quality of the sound. Significant differences were found between hearing lung sounds and years of experience and professional position, but not with age, gender, and sound quality. This study demonstrated that most of the tested examiners have the ability to hear heart and lung sounds at the extreme of loudness found in one ED.

Environmental geophysics investigations in urban areas

Dr John M. Reynolds, managing director and principal geophysicist at Reynolds Geo- Sciences, presents some case histories illustrating how the obstacles of noisy urban sites have been overcome to produce highly useful interpretable data sets, often far exceeding the expectations of the clients involved. Urban areas represent some of the most challenging environments in which to undertake geophysical investigations. Restricted space, the necessity for traffic management, high ambient noise (electrical and vibration), underground utilities, etc. all help to complicate the design and setting out of the geophysical profiles or grids. In many cases, such sites could not be investigated as the acquisition methods, the type of equipment and subsequent data processing software were not readily available. Over the last few years, significant changes in the capabilities of the equipment and software have permitted geophysical surveys to be undertaken in these hitherto inappropriate areas. The first case history at Field Road, Reading, Berkshire, was by far the largest, most complex and technically challenging. It shows how with very careful survey design, particular attention to data acquisition, and specialist data reduction and modelling, a labyrinth of shallow chalk mine galleries were mapped successfully using micro-gravity. The second involved a housing development in northwest London where the intrusive investigations had failed to satisfy the requirements of the Environment Agency, the environmental regulator in England and Wales (Scotland has a separate but similar regulatory body). Furthermore, the client and his engineering advisers were sceptical about the use of geophysics. Despite the technical difficulties of a complex partially developed site, the geophysical investigation demonstrated clearly the benefits of such a survey when integrated with intrusive investigations targeted on the basis of the geophysical survey. The client and his advisers became keen advocates of the use of geophysics once the results were made known. The third example is a complete contrast to the first two in that, despite the site being in a town, it comprised open space. The method used was the tried and tested and now very well established technique using a Geonics EM31 ground conductivity meter. (Detailed descriptions of geophysical methods discussed here have been presented by Reynolds (1997)). It demonstrates that even simple, long established techniques used very simply can produce some very clear and graphic results. The last case history involved the development of a former landfill site in south Wales. The 12.6 ha site was being cleared and earthworks to level the site were well in progress. At this late stage, it was suggested that steel drums might have been buried on the site but their location was unknown. A detailed geophysical investigation on the extremely busy construction site was undertaken using predominantly magnetic gradiometry and drum graves were located successfully and proven by excavation. The additional feature of all these case histories has been the involvement of what has subsequently become known as an ‘Engineering Geophysics Adviser’, an extremely experienced geophysicist (or group of geophysicists) independent of the geophysical contractor. This role has been advocated within the most recent guidelines for the use of engineering (and environmental) geophysics (McDowell et al., 2002).

Cigarette smoking, occupational exposure to noise, and self reported hearing difficulties

Aims: To explore the interaction of smoking and occupational exposure to noise as risk factors for hearing difficulty in the general population. Methods: A questionnaire was mailed to 21 201...

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The underwater acoustic noise of five representative whale-watching boats used in the waters of west Maui was measured in order to study the effects of boat noise on humpback whales. The first set of measurements were performed on 9 and 10 March, close to the peak of the whale season. The ambient noise was relatively high with the major contribution from many chorusing humpback whales. Measurements of boat sounds were contaminated by this high ambient background noise. A second set of measurements was performed on 28 and 29 April, towards the end of the humpback whale season. In both sets of measurements, two of the boats were inflatables with outboard engines, two were larger coastal boats with twin inboard diesel engines and the fifth was a small water plane area twin hull (SWATH) ship with inter-island cruise capabilities. The inflatable boats with outboard engines produced very complex sounds with many bands of tonal-like components. The boats with inboard engines produced less intense sounds with fewer tonal bands. One-third octave band measurements of ambient noise measured on 9 March indicated a maximum sound pressure level of about 123 dB re 1 μPa at 315 Hz. The maximum sound pressure level of 127 dB at 315 Hz was measured for the SWATH ship. One of the boats with outboard engines produced sounds between 2 and 4 kHz that were about 8–10 dB greater than the level of background humpback whale sounds at the peak of the whale season. We concluded that it is unlikely that the levels of sounds produced by the boats in our study would have any grave effects on the auditory system of humpback whales.

Engine Test Cell Noise Emission Design with Performance Validation Results

An existing industrial test facility was proposed to be relocated from a plant site in a high ambient noise environment to a community with low ambient noise. The existing facility contained engine test cells and support equipment with loud noise emissions. The original location was in an industrial park, adjacent to a high-speed multi-lane divided highway, but residential communities were nearby. Few noise complaints had been received at the existing location. The proposed future site was in a semi-rural area, near a two lane, moderate speed roadway. Although some moderate environmental noise emissions existed from an industrial installation on the existing site, the potential was recognised for community noise disturbance from the introduction of a new noise source. JEAcoustics was retained to assess the ambient noise environments and noise emission characteristics for the purpose of determining attenuation requirements for the new facility. A consultant's confidentiality agreement with the owner prevents disclosure of the facility name, plant locations, discussion of plant processes or revelation of other proprietary information. This case study presents the findings of that effort and the noise criteria that were established. Noise control designs and product applications are discussed with results of postconstruction noise validation measurements.

Audio system design for cruise ships

The design of audio systems for cruise ships introduce several acoustic challenges. The two leading challenges to overcome are ambient noise level and specular reflections. Ambient noise levels can reach 55 dBA and in many cases, higher. A majority of these noises are caused by engine vibrations, and HVAC which tends to be the leading cause of high noise floor levels. Audio systems are designed to compensate for such high ambient noise levels by distributing sound levels selectively throughout the facility. Another challenge to audio system design is specular reflections. This reflection is a delayed audible signal bounced off a surface at equal to or slightly less than the level of the direct sound with time as the variable. The problems caused by these reflections can vary from tonal coloration to echoes. Many surface materials not found in traditional showrooms can have very low absorption coefficients around the 1000 Hz–4000 Hz margin. Such surface materials include heavy plated glass windows, smooth tile flooring, etc. Interaction with the Interior Architect is crucial when designing the audio system. Many of these common problems can be minimized by room modeling through computer simulators for acoustics in the design phase.

Acoustic interaction of humpback whales and whale-watching boats

The underwater acoustic noise of five representative whale-watching boats used in the waters of west Maui was measured in order to study the effects of boat noise on humpback whales. The first set of measurements were performed on 9 and 10 March, close to the peak of the whale season. The ambient noise was relatively high with the major contribution from many chorusing humpback whales. Measurements of boat sounds were contaminated by this high ambient background noise. A second set of measurements was performed on 28 and 29 April, towards the end of the humpback whale season. In both sets of measurements, two of the boats were inflatables with outboard engines, two were larger coastal boats with twin inboard diesel engines and the fifth was a small water plane area twin hull (SWATH) ship with inter-island cruise capabilities. The inflatable boats with outboard engines produced very complex sounds with many bands of tonal-like components. The boats with inboard engines produced less intense sounds with fewer tonal bands. One-third octave band measurements of ambient noise measured on 9 March indicated a maximum sound pressure level of about 123 dB re 1 μPa at 315 Hz. The maximum sound pressure level of 127 dB at 315 Hz was measured for the SWATH ship. One of the boats with outboard engines produced sounds between 2 and 4 kHz that were about 8–10 dB greater than the level of background humpback whale sounds at the peak of the whale season. We concluded that it is unlikely that the levels of sounds produced by the boats in our study would have any grave effects on the auditory system of humpback whales.

Ambient noise suppression circuit

An ambient noise suppression electrical circuit to be used with a voice communication terminal comprising a gain control amplifier, whose input is a microphone, and a peak-hold circuit that includes a band-pass amplifier that amplifies a specified frequency range of the output signals of the microphone, a peak detection circuit that produces signals in proportion to the peak level of the output signals of the band-pass amplifier, and a holding circuit that controls reduction of output signals of the peak detection circuit for a specified period of time. The output signal from the peak-hold circuit controls the gain of the gain control amplifier. When a microphone is located far from a mouth and is used under high ambient noise, the present invention makes it possible for the microphone to perform as if it is a microphone which is located in a quality telephone handset that cuts off ambient noise.

Auscultation of heart and lung sounds in high-noise environments using adaptive filters

The clinical utility of a stethoscope in an aircraft is limited by high ambient noise. An adaptive noise-reduction stethoscope was implemented and some of its capabilities evaluated. Noise-corrupted heart and lung sounds, and a noise estimate, were collected using a two-microphone coupler in a simulated aircraft environment with 80–100 dB(SPL) ambient noise. Two adaptive filtering algorithms were compared: least mean square (LMS) and normalized LMS (NLMS). For frequencies between 20 and 800 Hz, the NLMS approach yielded roughly a 25% improvement in the extracted signal-to-noise ratio (SNR), while also providing a reduced adaptation time. Coupler chamber geometry was then examined by comparing two designs, one with a cylindrical microphone chamber and the other conical. There was no observable difference between the extracted signals due to this geometry change. Noise source independence was also investigated through comparison of algorithmic performance for C-130 aircraft and helicopter noise. Helicopter noise yielded an 18% lower SNR than C-130 noise due primarily to its relatively larger low-frequency spectral content. Thus a stethoscope using adaptive filters holds promise to extract heart and lung sounds from high ambient noise environments, with the NLMS providing some performance enhancements under certain conditions.

Use of otoacoustic emissions to screen for hearing loss in critically ill patients.

As part of a continuing quality improvement program, this project was undertaken to define the frequency of hearing loss in patients admitted to a surgical intensive care unit in order to identify patients at risk for impaired communication. The study evaluated 168 consecutive admissions over a ten week period to a ten bed adult surgical intensive care unit in a university hospital. Patients were screened as close to admission to the ICU as possible with otoscopy, tympanometry, and distortion product otoacoustic emissions. A total of 113 patients (226 ears, mean age 58.0+/-15.8 years) were screened within 1.5+/-1.4 days of ICU admission; 55 of the 168 admissions could not be screened (48 out of 55 due to short ICU stays). Of the 226 ears evaluated, 6.6 per cent had abnormal otoscopy and 43.2 per cent abnormal tympanograms. OAE failure occurred in 58.4 per cent of ears while OAE results were uninterpretable due to high ambient noise in 2.7 per cent of ears, and technical difficulty in 3.5 per cent of ears. Mean time for screening was 9.3 minutes. OAEs provide an efficient screening modality for hearing impairment in critically ill adults. The results suggest a significant prevalence of hearing impairment in the population studied. More definitive testing should be considered when clinically indicated in patients who fail OAE screening.

Hearing Thresholds, Threshold Repeatability, and Attenuation Values For Passive Noise-Reducing Earphone Enclosures

Passive noise-reducing earphone enclosures contain a supra-aural earphone mounted in a plastic dome. These enclosures are used to prevent the elevation of hearing thresholds due to masking from high levels of ambient noise. This research determined normal hearing threshold levels, threshold repeatability, and attenuation values for an Audiocup, Auraldome II, AudioMate, and Madsen ME-70 enclosure. In Study I hearing thresholds were obtained for 30 normally hearing adults from 500 to 6000 Hz in four test sessions for each enclosure and a supra-aural earphone attached to a headband. The hearing thresholds and repeatability for the Audiocup and Auraldome were similar but the thresholds were higher and repeatability was poorer for the AudioMate and Madsen ME-70 compared with the supra-aural earphone. In Study II real-ear attenuation values were obtained for each enclosure using 24 normally hearing subjects. The Audiocup and Auraldome II provided less low-frequency attenuation compared with the AudioMate and Madsen ME-70. The findings were related to the coupling of the supra-aural earphone in each enclosure to the ear and the coupling of each enclosure to the head. If an enclosure is used as an alternative to a supra-aural earphone for hearing testing in high ambient noise environments, hearing thresholds and threshold repeatability should be similar to a supra-aural earphone, and the enclosures should provide adequate attenuation of ambient noise. Since none of the enclosures met all of these requirements their use is not recommended for hearing testing.

Hearing Thresholds, Threshold Repeatability, and Attenuation Values For Passive Noise-Reducing Earphone Enclosures

Passive noise-reducing earphone enclosures contain a supra-aural earphone mounted in a plastic dome. These enclosures are used to prevent the elevation of hearing thresholds due to masking from high levels of ambient noise. This research determined normal hearing threshold levels, threshold repeatability, and attenuation values for an Audiocup, Auraldome II, AudioMate, and Madsen ME-70 enclosure. In Study I hearing thresholds were obtained for 30 normally hearing adults from 500 to 6000 Hz in four test sessions for each enclosure and a supra-aural earphone attached to a headband. The hearing thresholds and repeatability for the Audiocup and Auraldome were similar but the thresholds were higher and repeatability was poorer for the AudioMate and Madsen ME-70 compared with the supra-aural earphone. In Study II real-ear attenuation values were obtained for each enclosure using 24 normally hearing subjects. The Audiocup and Auraldome II provided less low-frequency attenuation compared with the AudioMate and Madsen ME-70. The findings were related to the coupling of the supra-aural earphone in each enclosure to the ear and the coupling of each enclosure to the head. If an enclosure is used as an alternative to a supra-aural earphone for hearing testing in high ambient noise environments, hearing thresholds and threshold repeatability should be similar to a supra-aural earphone, and the enclosures should provide adequate attenuation of ambient noise. Since none of the enclosures met all of these requirements, their use is not recommended for hearing testing.

Methods for automatic detection of mysticete sounds

Methods for the automatic recognition of low‐frequency sounds of baleen whales are presented. Matched filtering is implemented with a synthetic filter kernel derived from measurements of whale sounds, and this method is found effective at detecting blue whale (Balaenoptera musculus) sounds in white background noise. Spectrogram correlation is implemented and found effective at detection of blue whale vocalizations in the presence of interfering sounds. Spectrogram correlation employs image correlation using spectrograms and carefully designed image kernels to give good performance in the presence of noise. The two methods are briefly compared. The effectiveness of the spectrogram correlator is also demonstrated with finback whale (B. physalus) sounds. A supplementary method for detecting regular, repetitive sequences of sounds is applied to minke whale (B. acutorostrata) pulse trains, and found to improve detection in conditions of high ambient noise.

Shooting direction and crosswell seismic data acquisition

Four crosswell seismic surveys were acquired in the Glenn Pool Field of northeastern Oklahoma as part of a multidisciplinary reservoir characterization project. The acquisition goal was to generate data suitable for tomographic traveltime inversion. Acquisition parameters and shooting geometry were selected by conducting a parameter test at the site. Following the parameter test, the first survey resulted in high quality data showing clear first arrivals, low ambient noise, some reflection events, and strong source‐generated tube waves. The second survey involved a different receiver well and encountered high ambient noise levels. The noise was strong enough to prohibit first‐arrival picking for much of the data. On‐site analysis of the second survey revealed tube waves emanating from a perforated interval in the receiver well. This well was shut in and was not flowing fluid or gas at the surface. We interpret the source of ambient tube waves as borehole‐to‐formation fluid flow (circulation) associated with the perforations. Since this image plane was important for characterization of the reservoir, the survey was reshot (third survey) by reversing sources and receivers in the two wells. The resulting high‐quality data indicates that shooting direction can be an important factor in crosswell seismic acquisition. This experience influenced acquisition of a previously planned fourth survey so that the ambient noise problem would be avoided.

The effects of chronic industrial noise exposure on urinary cortisol, fatigue and irritability: a controlled field experiment.

This quasiexperimental field study explored the effect of noise attenuation on urinary cortisol excretion (sampled three times, at 6:30 and 10:30 AM and 1:30 PM) and reported fatigue and postwork irritability among 35 healthy industrial workers chronically exposed to high ambient noise levels (> 85 dB [A]) without using ear protectors. The results indicated that under conditions of chronic noise exposure the cortisol level at the end of the workshift was high and almost reached the morning level. This elevation in cortisol excretion was accompanied by high levels of accumulated fatigue and postwork irritability. Attenuating the noise reaching the eardrum by 30 to 33 dB, by fitting the same workers with earmuffs for a period of 7 working days, resulted in a significant improvement in both psychological and physiological stress reactions. Besides decreasing noise intensity, no other changes were made, either to ongoing work activities or to the other characteristics of the ambient noise. The cortisol level declined steadily during the workshift and exhibited the normal cortisol diurnal rhythm. At the end of the workshift, this level was significantly lower (P < .05) than that observed under the chronic noise-exposure condition. There was also a concomitant reduction in reported fatigue (P < .05) and postwork irritability (P < .01). These findings demonstrate the "net" contribution of ambient noise to elevating stress reactions to regular work demands.