Impulse Noise Levels Research Articles

Assessment of impulse noise level and acoustic trauma in military personnel.

Background:Military personnel are usually exposed to high levels of impulse noise (IN) which can lead to hearing loss.Objectives:The purpose of this study was to assess the effects of relatively low level exposure of impulse noise (IN) during shooting practice on hearing using pure tone audiometry (PTA) and transiently evoked otoacoustic emission (TEOAE) in military personnel.Materials and Methods:Forty male soldiers (mean age 20.08 years) were recruited for the study. Prior to their first shooting practice, PTA and TEOAE were recorded. After 15 minutes and one week post- practice PTA and TEOAE were compared.Results:Immediately after shooting practice significant differences in PTA at 500, 1000, and 4000 Hz were observed for the right ear and no significant difference at any frequency for the left ear. There was a significant difference in the amplitude of TEOAE 15 minutes after shooting practice at 500, 1000, 2000, 3000, and 4000 Hz in the right ear, while for the left ear the difference was significant at 1000 and 2000 Hz. One week after exposure a significant difference at 500 and 4000 Hz was found only in the right ear and a significant difference in the amplitude of TEOAE was observed at 500, 1000, 2000, 3000, and 4000 Hz.Conclusions:Even exposure lower than permissible levels may lead to acoustic trauma. TEOAE is more sensitive than PTA in detecting early hearing loss after military shooting exercises. Hearing protection equipment and appropriate surveillance programs are recommended.

Noise Exposure Assessment in a Dental School

ObjectivesThis cross-sectional study was performed in the Dental School of Prince of Songkla University to ascertain noise exposure of dentists, dental assistants, and laboratory technicians. A noise spectral analysis was taken to illustrate the spectra of dental devices.MethodsA noise evaluation was performed to measure the noise level at dental clinics and one dental laboratory from May to December 2010. Noise spectral data of dental devices were taken during dental practices at the dental services clinic and at the dental laboratory. A noise dosimeter was set following the Occupational Safety and Health Administration criteria and then attached to the subjects' collar to record personal noise dose exposure during working periods.ResultsThe peaks of the noise spectrum of dental instruments were at 1,000, 4,000, and 8,000 Hz which depended on the type of instrument. The differences in working areas and job positions had an influence on the level of noise exposure (p < 0.01). Noise measurement in the personal hearing zone found that the laboratory technicians were exposed to the highest impulsive noise levels (137.1 dBC). The dentists and dental assistants who worked at a pedodontic clinic had the highest percent noise dose (4.60 ± 3.59%). In the working areas, the 8-hour time-weighted average of noise levels ranged between 49.7-58.1 dBA while the noisiest working area was the dental laboratory.ConclusionDental personnel are exposed to noise intensities lower than occupational exposure limits. Therefore, these dental personnel may not experience a noise-induced hearing loss.

Evaluation of hearing protection devices with high-amplitude impulse noise

Presently, the evaluation of HPDs (hearing protection devices) is mainly based on audiometric threshold methods. However, in the military environment soldiers may be exposed to impulse noise levels of 190 dB and higher if large caliber weapons or IEDs (improvised explosive devices) are considered. In this case it seems reasonable to expect that an evaluation done at hearing threshold might not represent the protection which will be encountered at these highest levels. Therefore, it is necessary to evaluate the HPDs with signals close to the effective exposure. ISL has developed procedures using explosive charges creating very high levels of impulse noise (up to 195 dB peak) for the evaluation of HPDs. ISL also has developed an artificial head that can withstand this type of exposure and has sufficient self-insertion loss for the measurement of double hearing protection. The presentation will give a description of the techniques used at the ISL. It will present some results showing the possibilities to determine the performance of different types of HPDs when subjected to extreme impulse noise levels. Moreover, the new version of the ISL artificial head, compatible ANSI-ASA-S12.42-2010, and possible problems when using it will be presented.

Prediction of optimal conditions for verbal-communication quality in eating establishments

This paper discusses the prediction of verbal-communication quality in eating establishments (EEs). EEs contain talkers and listeners who require high speech intelligibility at their tables, and high speech privacy between tables. Using catt-Acoustic, verbal-communication quality--quantified by speech transmission index (STI)--in models of three existing EEs was predicted. Talker voice-output levels were predicted using an existing empirical model accounting for the Lombard effect. With these, catt-Acoustic predicted impulse responses, speech levels and noise levels at primary and secondary listener positions, and the corresponding STIs. The untreated EEs were first modeled for various talker and listener positions, and occupancies. Then various treated configurations, involving reduced volume, increased absorption and barriers were studied to determine the effectiveness of the treatments. The results suggest that placing barriers around tables can be an effective way to achieve good verbal-communication quality. Increasing the absorption of the room surfaces or decreasing the ceiling height to control reverberation may not be effective. However, increasing the surface absorption and putting barriers around tables may achieve optimal speech conditions in EEs. Subdividing large EEs into smaller ones can also be effective.

Measuring recreational firearm noise.

Recreational use of firearms in the United States is commonplace. There are 28 × 106 Americans who consider themselves hunters and 13 × 106 went hunting in 2000. Participation in the shooting sports, without the use of properly worn hearing protection, exposes the involved persons to high levels of impulsive noise which may cause hearing loss and/or tinnitus (ear ringing). The present study was initiated to gain a better understanding of the noise exposure created by contemporary firearms using state of the art instrumentation and to ultimately increase our knowledge and awareness of this unique noise hazard. The sound pressure signal created by recreational firearms as used in hunting or target practice is characterized by a high-frequency, short duration impulsive noise. This signal is perceived by the human ear as one single, loud impulse or “shot.” However, when the firearm sound level is measured with microphones capable of sampling wide frequency ranges and combined with high-speed data acquisition computer systems, the impulses can be resolved into a number of different acoustic signals related to different source mechanisms.

Loudness Level and Annoyance of Impulsive Noise

Loudness Level and Annoyance of Impulsive Noise

Using indoor room criteria when the “room” is outside.

Indoor noise criteria have applicability in the analysis of outdoor performance spaces. The presentation will provide an overview of the environmental noise issues at the Jay Pritzker Pavilion in Chicago, IL. The project design was largely influenced by noise concerns, in its physical form, audio design strategy, and building systems design. During the postconstruction tuning of the audio system a number of parameters were adjusted to contend with the unusually low signal‐to‐noise ratio, including the overall loudness of amplified music, audio signal compression, the content and level of the acoustic enhancement system, and the approach to the active in‐house mix of the audio system. An investigation was also undertaken to investigate the continuous and impulsive noise levels and frequency content at various times of day as compared with traditional environmental noise criteria and indoor room criteria. Subsequent studies regarding the impact of nearby construction noise on rehearsals and performances were influenced by the use of indoor noise criteria methods.

Impulse and continuous noise reduction of tactical hearing protection systems

Tactical hearing protectors are devices designed to protect the wearer from high levels of impulse noise while providing some ambient listening and communication capability. Many of these devices also provide some attenuation of continuous noise. The efficacy of these types of devices depends on the amount of impulse noise protection and continuous noise protection, the quality of the ambient listening capability, and the intelligibility of the speech communication capability. This paper will describe the peak noise reduction of approximately 1 ms duration impulses with peak levels at 165 dB and 195 dB, for several earplugs and earmuffs. The frequency dependent reduction of impulse noise measured using an acoustic test fixture (the French German Research Institute at Saint Louis Head). Generally the data show higher levels of impulse noise reduction with earplugs than with earmuffs. Additionally, continuous noise attenuation was measured using human subjects performing the ANSI S12.6 Real Ear At Threshold (REAT) test. High speed (20k frames/sec) video will show the dynamic motion of typical tactical hearing protection earplugs and earmuffs when stimulated with a 195 dB impulse.

Modified minimum-maximum exclusive mean filter

In an environment of fierce noise contamination, infected pixels tend to connect into noise blotches that could give the filtering algorithm an illusion of being part of the original image data. Therefore, many impulses would be difficult to detect, with the consequence of a less chance for proper detection and thus, filtering. Previously, median filters or its variant have been adopted to filter image corrupted with impulsive noise. Although advanced techniques have been added to these filters, many details such as thin lines and edges are either lost or blurred, especially at high noise situation. In this paper, a filtering method that consists of two stages, namely impulse noise detection and noise filtering is proposed, where the two stages are carried out separately and iteratively. Through computer simulation, the effectiveness of the suggested filter has been proven, especially at the high impulse noise levels.

Development of artificial neural network classifier to identify military impulse noise

Civilian noise complaints from urban encroachment have curtailed military exercises that produce high levels of impulse noise. Currently, monitoring stations are in place around many military installations to monitor noise levels. However, these monitoring stations do not provide real-time data and suffer from false positive detections. This project sought to develop algorithms with improved noise classification accuracy. Various types of military impulse noise and nonimpulse noise were measured and processed. Approximately 1000 waveforms were field collected (670 nonimpulse and 330 military impulse). Although several metrics were examined, the conventional time domain metrics of kurtosis and crest factor as well as two novel frequency domain metrics, weighted square error and spectral slope, were found to work best. The computed metric values were used to train and verify the performance of the artificial neural network (ANN), which was able to achieve 100% accuracy on training data and 100% accuracy on verification data. [This research was supported wholly by the U.S. Department of Defense, through the Strategic Environmental Research and Development Program (SERDP).]

Regulating environmental noise in Minnesota

In Minnesota, environmental noise is regulated by the Minnesota Pollution Control Agency (MPCA) noise control rules (MN Rules 7030). Features of the MPCA noise rule include use of L10 and L50 to regulate maximum allowable daytime and nighttime noise (on a dBA basis), and use of the state environmental noise rule to limit maximum allowable levels of highway traffic noise. The MPCA noise rule is guided by provisions in Minnesota Statutes (MS 116.07). Among those provisions is the requirement that MPCA adapt noise rules that give due consideration to such factors ‘‘that could interfere unreasonably with the enjoyment of life and property.’’ This ambitious goal could be interpreted as having applicability to impulsive or ground‐borne noise. Yet MPCA noise rules clearly state that they ‘‘do not identify limiting levels of impulsive noise needed for the preservation of public health and welfare.’’ Budget cuts eliminated the MPCA noise unit, and ended their enforcement of the state noise rule. This paper discusses the MPCA rule, program, and current noise issues in Minnesota.

Guest Editorial: Noise and Health

Guest Editorial: Noise and Health

Dose and time-dependent protection of the antioxidant N--acetylcysteine against impulse noise trauma

Noise-induced hearing loss is one of the most common causes of hearing disability, and at present there is no effective biological protection or cure. Firearms and some industrial equipment can generate very high levels of impulse noise, which is known to cause sensorineural hearing loss. It has been shown that antioxidants such as N - l -acetylcysteine (NAC) can protect the inner ear from oxidative damage. The present study investigates whether NAC (i.p.) can protect the cochlea from impulse noise trauma. Rats were exposed to 50 noise pulses at 160 dB SPL peak value. Electrophysiological hearing thresholds were assessed with auditory brainstem response (ABR) up to 4 weeks after noise exposure. Animals exposed to impulse noise, without treatment of NAC, had larger threshold shifts in the frequency range 4–40 kHz than animals injected with NAC. Hair cell loss was significantly reduced using a schedule of three NAC injections in the rats. These results suggest that NAC can partially protect the cochlea against impulse noise trauma.

Dose and time-dependent protection of the antioxidant N- l-acetylcysteine against impulse noise trauma

Noise-induced hearing loss is one of the most common causes of hearing disability, and at present there is no effective biological protection or cure. Firearms and some industrial equipment can generate very high levels of impulse noise, which is known to cause sensorineural hearing loss. It has been shown that antioxidants such as N- l-acetylcysteine (NAC) can protect the inner ear from oxidative damage. The present study investigates whether NAC (i.p.) can protect the cochlea from impulse noise trauma. Rats were exposed to 50 noise pulses at 160 dB SPL peak value. Electrophysiological hearing thresholds were assessed with auditory brainstem response (ABR) up to 4 weeks after noise exposure. Animals exposed to impulse noise, without treatment of NAC, had larger threshold shifts in the frequency range 4–40 kHz than animals injected with NAC. Hair cell loss was significantly reduced using a schedule of three NAC injections in the rats. These results suggest that NAC can partially protect the cochlea against impulse noise trauma.

Firecrackers Noise

Fireworks are used all over the world to celebrate special occasions. Noise produced by firecrackers that are used to celebrate these occasions has been highlighted. This impulse type of noise can cause hearing damage. Noise measurements of firecrackers show that they produce high sound pressure peak levels. Typical firecracker impulse noise levels are given. Noise limits and measurement methods used for the fireworks in some countries are presented.

Design of a pulse generator and shock tube for measuring hearing protector attenuation of high-amplitude impulsive noise

The effectiveness of hearing protectors against high amplitude impulse noise levels remains the subject of research with objective testing techniques using acoustic test fixtures offering the only realistic method of providing rapid performance data for protector design and qualification. The work presented in this paper examines a prototype test method based on a shock tube and acoustic test fixture for the evaluation of protectors against high-level impulsive noise where established real ear attenuation at threshold methods would be impractical to apply. The results show that the system is capable of producing controlled repeatable high amplitude pressure pulses of variable duration for testing hearing protection devices in a grazing wave type test. A series of pilot tests illustrate how the system can have a sufficient self-insertion loss to reject flanking noise and allow the measurement of protector attenuations of up to 45 dB with little corruption from flanking noise.

Measurement of the impulsive noise environment for satellite-mobile radio systems at 1.5 GHz

Noise amplitude distribution measurements relevant to satellite-mobile radio systems are reported. The rationale for the measurements is outlined and the choice of measurement parameters justified. The measurement equipment and measurement methodology are described in detail. Results characterizing the elevation angle distribution of impulsive noise are presented for rural, suburban and urban environments and also for an arterial road (U.K. motorway) carrying high density, fast moving traffic. Measurements of the levels of impulsive noise to be expected in each environment for high- and low-elevation satellite scenarios using appropriate antenna configurations are also presented.

Air blast circuit breaker noise and hearing loss: a multifactorial model for risk assessment.

The assessment of the risk to hearing from impulse noise exposure may be a problem for the occupational physician because existing legislative and international noise exposure standards deal primarily with continuous noise, and are not valid in excess of the peak exposure limit of 200 pa (140 dB). Noise exposure in excess of this level, for example that due to firearms, is frequently perceived as harmful, but this is not necessarily the case, as impulse noise standards do, in fact, allow exposure with a maximum in the order of 6.3 kPa (170 dB). To illustrate this, a cross-sectional group of electrical transmission workers have been studied who were exposed to significant levels of impulse noise from air blast circuit breakers and firearms. Important hearing loss factors have been identified by means of a specially designed questionnaire. Using the Health & Safety Executive definition, the risk of hearing loss was determined by calculating prevalence odds ratios (ORs) for exposure to these factors. The OR for those with fewer than eight unprotected air blast circuit breaker exposures was 2.27 (95% confidence interval (CI), 1.01-5.08), whilst for those with more than eight exposures the OR was 2.10 (95% CI, 0.97-4.54). For firearm exposure, ORs of 1.61 (95% CI, 0.95-2.74) were noted in the medium exposure group and 2.05 (95% CI, 1.08-3.86) in the high exposure group. When all the factors were included in the model, the most significant factor was age. The study gives support to the impulse noise exposure criteria, confirming the borderline risk from air blast circuit breaker noise exposure and the relative safety of moderate gunfire exposure.

Acoustic modeling and measurements of hearing protectors for impulsive noise

REAL is the world-wide common method used for the hearing protector attenuation measurement in accordance with ISO 4869 and ANSI S12.6. This method is not suitable to determine the attenuation of the peak level of impulsive noise, because it measures the attenuation subjectively at low levels of a steady-state sound near the threshold of hearing. Alternative low cost and quick methods are required for assessing hearing protector attenuation for impulsive noise. In this paper a numerical model based on the finite-element method (FEM) for the impulsive noise attenuation prediction of the hearing protector is presented. The insertion loss of the peak level in the time domain is calculated and compared with laboratory measurements.

Physiological cost of energy-equivalent noise exposures with a rating level of 85 dB(A):: Hearing threshold shifts associated with energetically negligible continuous and impulse noise

In industry continuous or impulse noise does not occur exclusively; rather it is a combination of both. If low-level continuous noise or impulse noise (below 120 dB) is added to an already existing high-level continuous noise this often numerically causes no essential increase in the rating level. Yet, it cannot be expected that also aural strain of these exposures is always negligible. Therefore, in a cross-over test series, ten male subjects (Ss) were exposed to white noise of 94 dB(A) for 1 h (TS I), energy-equivalent to an 8 h-rating level L Ard of 85 dB(A). In a second test series (TS II) the same exposure was combined with 900 energetically negligible 5-ms impulses with a noise level of 113 dB(A) which increased the rating level by only 0.4 dB. The noise exposure of TS I and TS II was followed by an idealized resting phase in a soundproof cabin. In a third test series (TS III) the continuous noise of 94 dB(A) / 1 h was followed by 3 h of white noise at 70 dB(A). Such an additional load increases the L Ard by merely 0.1 dB to 85.1 dB(A). In all three test series, the noise-induced temporary threshold shift (TTS 2) and its restitution were measured. The continuous noise exposure of 94 dB(A) for 1 h was associated with a TTS 2 of around 20 dB which disappeared completely after about 2 h. The additional impulse noise caused a small increase in the TTS 2 and a prolongation of the restitution time. The maximum mean temporary threshold shift for the group increased only slightly (from 22.5 to 25.9 dB, which nevertheless can be statistically proven at a significance level of p ⩾0.99). Yet, more importantly, the restitution time increased from 126 to 175 min, i. e. 3 h, which can be statistically proven at a significance level of p⩾0.95. The TTS 2-values of TS III did not differ significantly from those resulting from TS I. That was expected as the conditions up to that point in time were identical. But due to the additional subsequent exposure, the mean restitution time increased considerably from 126 min up to 240 min (4 h). The mean total physiological cost represented by the integrated restitution temporary threshold shift (IRTTS) increased in TS II by approximately 40% and in TS III even by 140%. Relevance to industry The results of the study show that levels of noise which have no influence on the rating level which traditionally is calculated according to the energy-equivalence principle are often of great importance, as they can lead to considerably prolonged restitution times. Therefore, the purely energy-equivalent determination of the rating level of both impulse noise and low sound levels can lead to an underestimation of latent problems so that over time a reversible TTS can evolve into a permanent threshold shift. The results are also of importance for the acoustic design of break rooms for noise-exposed workers. There should be conditions that allow an undisturbed restitution of hearing.