Peak Sound Pressure Level Research Articles

Impulse noise reduction for hearing protectors.

In 2009, the United States Environmental Protection Agency will propose a revision to the federal regulation for the labeling of hearing protection devices, 40 CFR 211 Subpart B. One of the new features of the proposed rule was the measurement of an impulse noise reduction rating for hearing protection devices. Measurement of impulsive sounds is challenging technically from an acoustics perspective. This paper will report on the performance of an acoustic shock tube used to generate impulses between 140 and 170 dB peak sound pressure level. The calibration methods for the microphones will be discussed and the measurements for a variety of hearing protectors will be presented. Typical earmuffs are capable of impulsive noise reduction ratings of between 20 and 35 dB. Earplugs provide similar range of performance. Combinations of earmuff and earplug have yielded impulse peak reductions of more than 50 dB. The reduction of the impulse peak level should provide a means to predict exposure at the ear when a hearing protector is worn in an impulsive noise environment.

Noise Exposure Levels in Stock Car auto Racing

Noise-induced hearing loss associated with the workplace has been well described. Far less is known, however, about the risks to hearing from recreational sources of noise. We investigated the popular sport of stock car racing as a potentially significant source of noise exposure, and we conducted a sound-level survey at a National Association for Stock Car Auto Racing (NASCAR) event. Noise levels measured during the race ranged from 96.5 to 104 dB(A) at 46 meters ( approximately 150 feet) from the track and 99 to 109 dB(A) at 6 meters ( approximately 20 feet) from the track. The peak sound pressure level at 6 meters was 109 dB(A). Although significantly less than that associated with an immediate permanent threshold shift, such an exposure could cause a temporary threshold shift. Alhough hearing protection is recommended, particularly for track employees with longer periods of exposure, racing fans with only occasional exposure to such noise levels are unlikely to develop a permanent noise-induced hearing loss.

Amplitude of bison bellows reflects male quality, physical condition and motivation

Sound amplitude (measured as sound pressure level) is an acoustical parameter that has received little attention within communication research, especially in mammals. Although difficult to measure in the field, amplitude is a potentially important parameter of sexually selected signals. In North American plains bison, Bison bison, ‘bellows’ are low, guttural vocalizations made by bulls during the breeding season in the context of male–male contests. It has been hypothesized that bison use bellow amplitude to assess males during male–male competition or female mate choice. In this study, we tested the hypothesis that amplitude is significantly related to measures of bull competitive ability (quality, condition and motivation), and thus, could function as a sexually selected signal. During peak rut over 2 years, courtship and threat behaviours were recorded daily. During observation sessions, bellow amplitude was measured as peak sound pressure levels using a sound level meter. Subsequent genetic parentage analysis determined offspring sired by males. Based on aspects of signalling and game theory, we predicted positive associations between amplitude and mating and reproductive success, dominance, physical condition, motivation to retain females, age and weight. Our results supported a positive association between amplitude and both physical condition and motivation. Conversely, the results showed a negative association between amplitude and quality, as measured by mating and reproductive success. Supporting evidence and alternative hypotheses for these results are explored. Our findings provide support for the notion that bellow amplitude could be used as a sexually selected signal to assess rival males during male–male competition.

A comparison of impulse-like sources to be used in reverberation time measurements

As a part of an extensive ongoing research on reverberation time measurements, efforts have been made to find an impulse-like source that will comply with certain demands concerning its spectral content and sound pressure levels it can provide. Although the relevant standards state that such kind of sources should be avoided due to the lack of measurement repeatability, their use has proved to be necessary due to inability of conventional omni-directional loudspeakers to provide adequate sound pressure levels, especially at the low end of the frequency range of interest, thereby ensuring sufficient dynamic range. Therefore, the emphasis of this investigation has been made on peak sound pressure levels and the amount of low frequency content each source is able to provide. The investigated sources include 6 mm and 8 mm pistols, firecrackers with different amount of explosive compound and explosive mixtures of acetylene gas.

Describing the sound environment of the neurological intensive care unit and personnel response

The hospital soundscape is populated with a number of noise sources that may be detrimental to the occupational environment, including medical equipment, alarms, portable carts, activities, paging/communication, and ventilation systems. This paper describes a study in which sound measurements were made over five days and occupant evaluations were conducted in a neurological intensive care unit (ICU). Forty-seven nursing staff members completed questionnaires regarding general reactions to the ICU environment as well as perceived psychological and physiological reactions to the noise. Acoustical characteristics such as level distributions, restorative periods, and spectral content were explored in addition to overall equivalent, minimum, maximum, and peak sound pressure levels. Results showed the mean length of restorative periods (LAeq below 50 dB for more than 5 min) was 9 and 13 minutes for day and night, respectively. Sound measurements near the patients showed LAeq values of 53 - 58 dB, and dosimeters worn by the personnel revealed higher noise levels. Questionnaire results indicated that 91% of those surveyed felt that the noise negatively affected them in their daily work environment. They perceived the noise as contributing to stress symptoms such as irritation, fatigue, tension headaches, and difficulties concentrating. [Work supported by ASA and Swedish FAS].

Proposed Marine Mammal Noise Exposure Criteria: Current Data Base, Limitations, and Research Needs

This paper presents the findings of an inter-disciplinary expert panel based on comprehensive review of hearing and noise effects data for marine and land mammals. The principal motivation for the review was to assist formulation of data-based noise exposure criteria in light of rapidly evolving research advances in marine mammal hearing and underwater noise effects. Levels estimated to induce permanent hearing loss were determined for single exposure events for cetaceans (in water) and pinnipeds (in air and water) for each of 15 sound type/animal group combinations. These recommendations represent a current best estimate only and are modular, with modifiable key variables; e.g., source and exposure, to facilitate revision as data improve. In some cases, relatively explicit injury limits are proposed, e.g., 186 dB re: 1μPa2-s (frequency-weighted sound exposure level) and 218 dB re: 1μPapeak (unweighted peak sound pressure level) for pinnipeds in water exposed to multiple sound pulses. In others, particularly for behavioural effects of multiple-pulse and non-pulse exposures, response severity and significance are quantitatively scored, but the data do not allow identification of specific broadly-applicable disturbance thresholds. These findings are a current best effort and include a discussion of limitations and recommended research needed to address data gaps.

Use of actimeters to determine awakenings by sounds of large guns

The U.S. Army has been using the day-night average sound level (DNL) to manage the community noise impact from heavy weapons noise since the late 1970's. In this case, the DNL is C-weighted as recommended by the National Academy of Sciences-National Research Council Committee on Hearing, Bioacoustics and Biomechanics (CHABA). CHABA's recommendation was justified by the fact that C-weighting (originally developed for the loudness of intense sounds) measures lower frequency sound energy in large guns which is otherwise missed by A-weighting. When the CHABA methodology was first adopted, there was relatively little night firing, but, today, night vision technology makes firing during darkness an absolute necessity for military readiness. Recognizing that the 10-dB penalty incorporated in the DNL methodology was not intended to predict sleep disturbance and that sleep disturbance may be a function of discrete noise event levels rather than annual-average noise levels, the U.S. Army Engineer Research and Development Center initiated a project to measure sleep disturbance among people living near tank gunnery ranges. A first step in this project was to evaluate whether a commonly-used instrument for measuring sleep disturbance, the actimeter, would be sensitive to awakenings from blast noise. After preliminary screening of three designs of actimeter, the preferred design was tested in cooperation with the Army Center for Health Promotion and Preventive Medicine with subjects sleeping inside the Army Research Laboratory's Hostile Environment Simulator. Subjects were exposed to nighttime blasts at two linear peak sound pressure levels (110 dB and 120 dB). The results confirmed that the preferred design would be a reliable and rugged instrument for the actual field study of awakening from live fire. This article is a government work and as such, is in the public domain and not subject to copyright.

Noise in the operating rooms of Greek hospitals

This study is an evaluation of the problem of noise pollution in operating rooms. The high sound pressure level of noise in the operating theatre has a negative impact on communication between operating room personnel. The research took place at nine Greek public hospitals with more than 400 beds. The objective evaluation consisted of sound pressure level measurements in terms of L(eq), as well as peak sound pressure levels in recordings during 43 surgeries in order to identify sources of noise. The subjective evaluation consisted of a questionnaire answered by 684 operating room personnel. The views of operating room personnel were studied using Pearson's X(2) Test and Fisher's Exact Test (SPSS Version 10.00), a t-test comparison was made of mean sound pressure levels, and the relationship of measurement duration and sound pressure level was examined using linear regression analysis (SPSS Version 13.00). The sound pressure levels of noise per operation and the sources of noise varied. The maximum measured level of noise during the main procedure of an operation was measured at L(eq)=71.9 dB(A), L(1)=84.7 dB(A), L(10)=76.2 dB(A), and L(99)=56.7 dB(A). The hospital building, machinery, tools, and people in the operating room were the main noise factors. In order to eliminate excess noise in the operating room it may be necessary to adopt a multidisciplinary approach. An improvement in environment (background noise levels), the implementation of effective standards, and the focusing of the surgical team on noise matters are considered necessary changes.

Attenuation of high-level impulses by earmuffs

Attenuation of high-level acoustic impulses (noise reduction) by various types of earmuffs was measured using a laboratory source of type A impulses and an artificial test fixture compatible with the ISO 4869-3 standard. The measurements were made for impulses of peak sound-pressure levels (SPLs) from 150 to 170 dB. The rise time and A duration of the impulses depended on their SPL and were within a range of 12-400 mus (rise time) and 0.4-1.1 ms (A duration). The results showed that earmuff peak level attenuation increases by about 10 dB when the impulse's rise time and the A duration are reduced. The results also demonstrated that the signals under the earmuff cup have a longer rise and A duration than the original impulses recorded outside the earmuff. Results of the measurements were used to check the validity of various hearing damage risk criteria that specify the maximum permissible exposure to impulse noise. The present data lead to the conclusion that procedures in which hearing damage risk is assessed only from signal attenuation, without taking into consideration changes in the signal waveform under the earmuff, tend to underestimate the risk of hearing damage.

Statistical mapping of sound-evoked activity in the mouse auditory midbrain using Mn-enhanced MRI

Manganese-enhanced MRI (MEMRI) has been developed to image brain activity in small animals, including normal and genetically modified mice. Here, we report the use of a MEMRI-based statistical parametric mapping method to analyze sound-evoked activity in the mouse auditory midbrain, the inferior colliculus (IC). Acoustic stimuli with defined frequency and amplitude components were shown to activate and enhance neuronal ensembles in the IC. These IC activity patterns were analyzed quantitatively using voxel-based statistical comparisons between groups of mice with or without sound stimulation. Repetitive 40-kHz pure tone stimulation significantly enhanced ventral IC regions, which was confirmed in the statistical maps showing active regions whose volumes increased in direct proportion to the amplitude of the sound stimuli (65 dB, 77 dB, and 89 dB peak sound pressure level). The peak values of the activity-dependent MEMRI signal enhancement also increased from 7% to 20% for the sound amplitudes employed. These results demonstrate that MEMRI statistical mapping can be used to analyze both the 3D spatial patterns and the magnitude of activity evoked by sound stimuli carrying different energy. This represents a significant advance in the development of MEMRI for quantitative and unbiased analysis of brain function in the deep brain nuclei of mice.

Assessment of Noise Exposure for Indoor and Outdoor Firing Ranges

The National Institute for Occupational Safety and Health (NIOSH) received an employee request for a health hazard evaluation of a Special Weapons Assault Team (SWAT) in January 2002. The department was concerned about noise exposures and potential hearing damage from weapons training on their indoor and outdoor firing ranges. NIOSH investigators conducted noise sampling with an acoustic mannequin head and 1/4 -inch microphone to characterize the noise exposures that officers might experience during small arms qualification and training when wearing a variety of hearing protection devices provided by the department. The peak sound pressure levels for the various weapons ranged from 156 to 170 decibels (dB SPL), which are greater than the recommended allowable 140 dB SPL exposure guideline from NIOSH. The earplugs, ear muffs, and customized SWAT team hearing protectors provided between 25 and 35 dB of peak reduction. Double hearing protection (plugs plus muffs) added 15–20 dB of peak reduction.

Noise in the operating rooms of Johns Hopkins Hospital

Very little reliable information exists on the sound levels present in an operating room environment. To remedy this situation, sound pressure levels of the operating rooms in Johns Hopkins Hospital were monitored before, during, and after operations. The data were analyzed to determine background sound levels, average equivalent sound levels L(eq), frequency distribution, and peak sound pressure levels L(peak). Each surgery was matched to the period of noise it produced permitting the association of sound levels with particular types of surgeries and the determination of various sound measures for classes of surgery (e.g., orthopedic, neurological, etc.). Averaging over many surgeries, orthopedic surgery was found to have the highest L(eq) at approximately 66 dB(A). Neurosurgery, urology, cardiology, and gastrointestinal surgery followed closely, ranging from 62 to 65 dB(A). By considering the L(peak) along with the L(eq) values, a pattern emerges for the various surgical divisions. Gastrointestinal and thoracic surgery are relatively quiet among the surgical divisions. Neurosurgery and orthopedics have sustained high sound levels. Cardiology surgery has a more moderate average sound level but includes brief periods of extremely high peak sound levels. For neurosurgery and orthopedic surgery, peak levels exceeded 100 dB over 40% of the time. The highest peak levels routinely seen during surgery were well in excess of 120 dB.

Ocena przydatności ochronników słuchu podczas narażenia na działanie hałasu impulsowego

It is generally agreed that impulse noise that occurs mainly in industrial processes, military forces and recreational target practice und hunting is especially hazardous to the ear. From the physical point of view the phenomenon is defined as an acoustic pressure disturbance of short duration less than 1 sec and high intensity with the peak sound pressure levels greater than 100 dB SPL. The study included 80 subjects (160 ears) aged 19-23 with correct tympanic membrane and thresholds measured by pure tone audiometry less than 20 dB. There were divided into two groups: I comprised 40 recruit soldiers put to the shooting training and group II consisted of 40 recruit soldiers using hearing protectors during shooting. Transient evoked otoacoustic emission (TEOAE) measurements were performed by ILO 292 Echoport Otodynamics device 3-5 min before shooting and then 2 min, 1, 2 and 3 hours respectively after shooting in both groups. It was found that the gunshot impulse noise from kbk AKMS rifle caused in group I temporary hearing threshold shift (TTS) for 1, 2, 3, 4 and 5 kHz frequencies of 1.07; 0.96; 1.41; 0.88 and 1.25 dB SPL respectively. TTS turned out to be maximum at 4 and 5 kHz and minimum at 1 and 2 kHz. In group II the soldiers used ear-muffs post-exposure changes were not significant. Short-term impulse noise generated by the rifle gunshots induced threshold shift of hearing. The usage of hearing protectors should be highly recommended because most of them seem to sufficiently attenuate impulse noise from firearms should be highly recommended because most of them seem to sufficiently attenuate impulse noise from firearms.

Occupational and recreational noise exposures at stock car racing circuits

Noise in stock car racing is accepted as a normal occurrence but the exposure levels associated with the sport have not been adequately characterized. Researchers from the National Institute for Occupational Safety and Health (NIOSH) conducted an exploratory assessment of noise exposures to drivers, pit crew, team staff, and spectators at three stock car racing events. Area measurements were made during race preparation, practice, qualification, and competition. Personal dosimetry measurements were conducted on drivers, crew members, infield staff, and spectators. Findings showed time-weighted averages (TWA) that ranged from 94 decibels A-weighted (dBA) for spectators to 114 dBA for car drivers. Peak sound-pressure levels exceeded the maximum allowable limit of 140 decibels (dB) during race competitions. Personal exposure measurements exceeded the NIOSH recommended exposure limit (REL) of 85 dBA as an 8-h TWA in less than a minute for one driver during practice, within 2 min for pit crew and infield staff, and 7 to 10 min for spectators during the race. Hearing protection use was variable and intermittent among crew, staff, and spectators. Among drivers and crew, there was greater concern for communication performance than for hearing protection.

Hearing loss in recreational shooters in Central Queensland: A pilot study

This paper reports on the hearing status of a sample of recreational shooters, and explores some of the audiological characteristics associated with firearms and hearing protection use. The use of firearms is one common source of exposure to non-occupational noise in rural areas of Australia, and is reportedly the leisure activity that poses the greatest threat to hearing. Gunfire noise is an intensely strong impulse noise, and differs from continuous noise in its extreme peak sound pressure level and its very short duration. Impulse noise over 175–180 dB experienced during shooting activities damages and destroys the fine mechanical elements of the ear, and causes damage to the outer hair cells of the cochlea, resulting in hearing loss. Even when hearing protection devices are worn, some indications of a temporary threshold shift (TTS) may be found indicating the acute effects of exposure. Noise exposure during recreational shooting is thus an important factor to be considered when assessing the hearing status of a rural population who may be engaged in shooting activities in addition to exposure from work-related sources of noise.

Probability density prediction of peak sound pressure levels from firecracker explosions

On New Year’s Eve and some festivals, we encounter a great number of firecracker explosions. The peak sound pressure levels originating from the explosions can cause annoyance, loss of hearing, fire hazards, serious personal injuries, and even death. The immission of a peak sound pressure level at a given location due to an individual firecracker depends mainly on its sound power, on the distance from the explosion, and on the sound pressure distribution in the time and frequency domain. In this paper, some practical measurements have been performed over a New Year’s Eve, and the results were compared with other days. A special emphasis is given to statistical aspects and the probability distribution function of peak sound pressure levels, originating from a great number of random firecracker explosions. Results have shown that the probability distribution closely follows the Rayleigh distribution, but, when the number of explosions per unit time is high enough, it tends to a Gaussian (normal) distribution.

Calibration of acoustic transients

This article reviews the appropriate stimulus parameters (click duration, toneburst envelope) that should be used when eliciting auditory brainstem responses from mice. Equipment specifications required to calibrate these acoustic transients are discussed. Several methods of calibrating the level of acoustic transients are presented, including the measurement of peak equivalent sound pressure level (peSPL) and peak sound pressure level (pSPL). It is hoped that those who collect auditory brainstem response thresholds in mice will begin to use standardized methods of acoustic calibration, so that hearing thresholds across mouse strains obtained in different laboratories can more readily be compared.

Extremely rapid induction of outer hair cell apoptosis in the chinchilla cochlea following exposure to impulse noise

We have reported the presence of OHC apoptosis and necrosis in the organ of Corti following exposure to intense noise. The current study was designed to investigate the rapidity and the initial pattern of outer hair cell (OHC) death induced by exposure to impulse noise. Chinchillas were exposed to 75 pairs of impulse noise at 155 dB peak sound pressure level presented over a time period of 75 s. At 5 or 30 min after the noise exposure, the cochleae were examined for morphological and biological indicators of apoptosis and necrosis. In the cochleae collected within 5 min after the 75-s noise exposure, there were clear signs of nuclear condensation and cell body shrinkage, suggesting the presence of OHC apoptosis. Apoptotic OHCs were further detected by positive staining of TUNEL and caspase-3 assays. In contrast to the rapid development of nuclear condensation, appearance of nuclear swelling, a necrotic phenotype, appeared at 30 min after the noise exposure. The results of the study demonstrate that induction of OHC apoptosis after the noise exposure is an extremely rapid process.

Noise Due to Firecracker Explosions

During New Year's Eve and some festivals some people are subjected to a great number of firecracker explosions. The peak sound pressure levels, originating from the explosions, can cause annoyance, fire hazards, loss of hearing, serious personal injuries, and even deaths. The immission of a peak sound pressure level at a given location due to an individual firecracker depends mainly on its sound power, the distance from explosion, and the sound pressure distribution in the time and frequency domain. In this paper, some practical measurements have been taken over a New Year's Eve and the results were compared with other days. Special emphasis is given to statistical aspects and probability distribution function of peak sound pressure levels, originating from a great number of firecracker random explosions. Results have shown that the probability distribution closely follows the Rayleigh distribution, but when the number of explosions in unit time is high enough, it tends to a Gaussian (normal) distribution.

Experimental study of aerosol concentration in flow-through, low-frequency resonators

An experimental method to study the concentration of micron-sized aerosols in a low-frequency sound field was developed. The physical mechanism for acoustic aerosol concentration in a low-frequency sound field is the asymmetric Stokes drag which has been predicted to exceed the effects of radiation pressure for typical aerosol sizes [Meegan and Ilinskii, J. Acoust. Soc. Am. 114, 2387 (2003)]. Related experiments were conducted in which 5 micron aerosol was drawn through a small duct that was driven in a transverse resonant mode with peak sound pressure levels of greater than 150 dB re 20 microPascals and frequencies in the range 1 to 10 kHz. The aerosol stream was illuminated by a laser sheet through the transparent walls of the duct in order to visualize (by video) the effects of the sound field. The experiments confirm the basic feature of the asymmetric Stokes drag model—specifically, the aerosol is observed to concen- trate along acoustic velocity nodes. Ongoing experiments to quantify the level of concentration will be described. [Work supported by RDECOM.]