Influence of a reduced wearing time on the attenuation of hearing protectors assessed via temporary threshold shifts

Valuable recommendations for the choice, utilization, care, and maintenance, and for the measurement of sound attenuation of hearing-protective devices have been laid down in international standards. Yet, by considering the wearing time of a hearing protector, the standard DIN EN 458 assumes a scarcely understandable drastic reduction in the effective attenuation even when the device is not used for only a short time in a noise-filled area. A 30 dB sound attenuation of such a protective device would, e.g., decrease to 12 dB if it were unused for only 30 min of an 8 h shift. Thus, the actual influence of a shortened wearing time on the protection of earmuffs was tested in a laboratory study using audiometric measurements of the temporary threshold shift (TTS₂) and its recovery after exposure to noise. For that purpose, the effectiveness of a hearing-protective device depending on the amount of time worn as prognosticated by DIN EN 458 was compared with the actual physiological effect of the earmuffs. Ten test subjects (Ss) participated in three test series (TS), each. In the first of the TS, the Ss were exposed to a sound pressure of 106 dB(A) for 1 h, during which the Ss wore noise-insulating earmuffs with an attenuation of 30 dB. The Ss were exposed to the same sound pressure in TS II; however, after 30 min, the earmuffs were removed for a duration of  min. Mathematically, this reduced the sound attenuation of the earmuffs to 12 dB, i.e., the average noise level over 1 h is 94 dB, which is equivalent to 85 dB(A) over 8 h. In order to evaluate the actual additional physiological cost of TS II, the Ss were exposed to 94 dB(A)/1 h without earmuffs in a third TS. This acoustic load, which is energy equivalent to the load in TS II, is also equivalent to 85 dB(A)/8 h. The results show that the continuous wearing of the earmuffs offers secure protection. However, the energetic approach and the levelling of differently structured noise loads according to the principle of energy equivalence leads to misconceiving results. The drastic reduction of the sound attenuation of the earmuffs predicted from the energetic point of view must be regarded as exaggerated. The TTS values show that TS II – which, according to the principle of energy-damage-equivalence, should result in the same effects as TS III – represents significantly less auditory fatigue. Thus, if the earmuffs are taken off briefly, a drastic reduction in the protection – as predicted in DIN EN 458 — does not result.

Relevance to industry

The results of this study demonstrate that the standards and regulations for noise rating do not correspond with the actual physiological facts and, therefore, can only be used in a very limited manner. Utilization of the principle of energy equivalence has proven problematic not only for rating noise. This principle also leads to an essential underestimation of the attenuation of hearing protectors when these devices are taken off for only a short time in a noise-filled area.     

The impact of hearing protection on sound localization and orienting behavior

The effect of hearing protection devices (HPDs) on sound localization was examined in the context of an auditory-cued visual search task. Participants were required to locate and identify a visual target in a field of 5, 20, or 50 visual distractors randomly distributed on the interior surface of a sphere. Four HPD conditions were examined: earplugs, earmuffs, both earplugs and earmuffs simultaneously (double hearing protection), and no hearing protection. In addition, there was a control condition in which no auditory cue was provided. A repeated measures analysis of variance revealed significant main effects of HPD for both search time and head motion data (p < .05), indicating that the degree to which localization is disrupted by HPDs varies with the type of device worn. When both earplugs and earmuffs are worn simultaneously, search times and head motion are more similar to those found when no auditory cue is provided than when either earplugs or earmuffs alone are worn, suggesting that sound localization cues are so severely disrupted by double hearing protection the listener can recover little or no information regarding the direction of sound source origin. Potential applications of this research include high-noise military, aerospace, and industrial settings in which HPDs are necessary but wearing double protection may compromise safety and/or performance.     

Effect of electronic ANR and conventional hearing protectors on vehicle backup alarm detection in noise

An experiment was conducted wherein masked thresholds (using ascending method of limits) for a backup alarm were obtained in pink and red noise at 85 and 100 dBA for 12 participants immersed in a probability monitoring task and wearing a conventional passive hearing protection device (HPD, an earmuff or a foam earplug), an active noise reduction (ANR) headset, or no HPD at all (only in 85 dBA noise). Results revealed statistically significant between-HPD differences in red noise (from 2.3 to 3.1 dB) and in the 100-dBA noise level (from 2.6 to 4.3 dB). An additional finding, which corroborates other studies using different protocols, was that masked thresholds in 85-dBA noise were significantly lower (from 3.2 to 4.4 dB) for the occluded conditions (wearing an HPD) than for the open-ear (unoccluded) condition. This result refutes the belief among many normal-hearing workers that the use of HPDs in relatively low levels of noise compromises their ability to hear necessary workplace sounds. Actual or potential applications of this research include (a) the selection of appropriate HPDs for low-frequency-biased noise exposures wherein signal detection is important and (b) gaining insight into the appropriateness of ANR-based HPDs for certain industrial noise environments.     

Passenger comfort on high-speed trains: effect of tunnel noise on the subjective assessment of pressure variations

When passing through a tunnel, aerodynamic effects on high-speed trains may impair passenger comfort. These variations in atmospheric pressure are accompanied by transient increases in sound pressure level. To date, it is unclear whether the latter influences the perceived discomfort associated with the variations in atmospheric pressure. In a pressure chamber of the DLR-Institute of Aerospace Medicine, 71 participants (M = 28.3 years ± 8.1 SD) rated randomised pressure changes during two conditions according to a crossover design. The pressure changes were presented together with tunnel noise such that the sound pressure level was transiently elevated by either +6 dB (low noise condition) or +12 dB (high noise condition) above background noise level (65 dB(A)). Data were combined with those of a recent study, in which identical pressure changes were presented without tunnel noise (Schwanitz et al., 2013, ‘Pressure Variations on a Train – Where is the Threshold to Railway Passenger Discomfort?’ Applied Ergonomics 44 (2): 200-209). Exposure-response relationships for the combined data set comprising all three noise conditions show that pressure discomfort increases with the magnitude and speed of the pressure changes but decreases with increasing tunnel noise.

Practitioner Summary: In a pressure chamber, we systematically examined how pressure discomfort, as it may be experienced by railway passengers, is affected by the presence of tunnel noise during pressure changes. It is shown that across three conditions (no noise, low noise (+6 dB), high noise (+12 dB)) pressure discomfort decreases with increasing tunnel noise.     

In-ear noise dosimetry under earplug: Method to exclude wearer-induced disturbances

While personal noise exposure assessments are necessary to prevent noise-induced hearing loss in the workplace, standard personal noise dosimeters are limited when measuring the noise exposure of individuals wearing hearing protection devices (HPD). To overcome the difficulties in assessing the attenuation provided by HPDs, continuous monitoring systems of an individual's noise exposure under the HPD show promise. However, these systems can be affected by the noise events induced by the wearer, though research has shown that the risk of hearing loss inherent to self-generated sounds (voice, swallowing, chewing) can be less than for external noise. This paper presents a low computational method to perform in-ear noise dosimetry under an earplug while excluding the noise contributions from the wearer. The method uses a dual-microphone earpiece able to take measurements both under the earplug and outside the ear. A comparison of the two microphones signals, through coherence calculations, provides sufficient information as to whether the protected noise levels originate mainly from the wearer or from external noise sources. Laboratory results collected on human test-subjects suggest that the proposed method is not only valid for a wide variety of self-generated sounds, it is efficient regardless of the amount of attenuation provided by the earplug. Further work involves validating the approach and parameters in occupational settings, and adapting this method to other types of HPDs such as earmuffs or dual hearing protection.     

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 (TTS₂) and its restitution were measured. The continuous noise exposure of 94 dB(A) for 1 h was associated with a TTS₂ of around 20 dB which disappeared completely after about 2 h. The additional impulse noise caused a small increase in the TTS₂ 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 p0.95. The TTS₂-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.     

A straightforward design technique for narrowband multi‐stage low‐noise amplifiers with I/O conjugate match

Low‐noise amplifier (LNA) designers often struggle to simultaneously satisfy gain, noise, stability, and I/O matching requirements. In this article, a novel design technique, tailored for two‐stage low‐noise amplifiers, is presented. The proposed design method is completely deterministic and exploits inductive source degeneration to obtain a two‐stage LNA featuring perfect input and output match together with low noise figure (NF) and a pre‐determined gain, including stability analysis. A novel flowchart is provided together with the corresponding design chart that contains gain, matching, and stability information, therefore addressing all key figures‐of‐merit of a linear amplifier. The design chart is easily implementable in commercial Electronic Design Automation software, to aid designers in the difficult task of selecting the appropriate source degeneration inductor value. The noise performance, on the other hand, is the best possible since the matching networks are designed to provide the input of the two Field Effect Transistors with the optimum termination for noise. The design method is validated with two separate test vehicles operating respectively at Ka‐band (26.5‐31.5 GHz) and K‐band (20.0‐24.0 GHz). The realized Monolithic Microwave Integrated Circuits exhibit 18 dB gain for both versions, NF of 1.5 and 1.2 dB, respectively for the Ka‐band and K‐band version. Input and output matching are typically better than 12 and 15 dB.     

Impacts of leisure activity noise levels on safety procedures and policy in the industrial environment

Prior research has concentrated on noise levels in the workplace. However, people who work in noisy environments might also have noisy leisure activities which could contribute to hearing loss or interfere with recovery time. This study investigated work and leisure noise levels experienced by workers in a manufacturing plant. Workers were surveyed to determine leisure activities and use of hearing protection. Measurements were taken to compare noise levels of the leisure activities with those in the workplace. Noise levels of the leisure activities had a mean of 99 dB with a standard deviation of 8 dB, while the mean for the noise levels in the work place was 89 dB with a standard deviation of 8 dB. Although workers are required to wear hearing protection when exposed to occupational noise levels above 85 dB, only 36% of the survey respondents wear hearing protection in the leisure environment.

Since the cost of hearing loss is frequently borne by organizations, even though some of loss might be attributable to leisure activities, it is prudent for facility engineers and plant managers to provide educational information emphasizing noise levels and associated risks for specific leisure activities, as well as to provide protection to employees for leisure use.     

电梯轿厢噪声主动控制系统与实验

针对高速电梯运行过程中所产生的轿厢噪声,基于主动噪声控制(ANC)技术,设计并开发了一个3入1出的多通道DSP自适应控制系统。利用该系统在模拟电梯环境中,分别针对130 Hz单频正弦噪声,正弦加白噪声和录取的电梯轿厢嗓声进行了控制实验,获得了20 dB,12 dB,8 dB的降噪效果,验证了本文系统在高速电梯轿厢噪声控制中的可用性和有效性。     

A broadband hybrid GaN cascode low noise amplifier for WiMax applications

This article reports a Microstrip design for low noise amplifier (LNA) using a packaged commercial GaN‐on‐SiC high electron mobility transistor (HEMT). A cascode configuration with an inter‐stage matching and an independent biasing technique was used. A lumped elements design was first developed, analyzed, and simulated in ADS. Then the design was implemented using microstrip technology and simulated using the momentum EM simulation in ADS. The LNA is easy to fabricate, has a low cost, and can be easily modified for other applications. The proposed GaN LNA showed a gain of 13.5 dB with a noise figure (NF) of 3 dB from 2.8 to 3.8 GHz.     

A new measurement microphone based on MEMS technology

This paper presents a new type of measurement microphone that is based on MEMS technology. The silicon chip design and fabrication are discussed, as well as the specially developed packaging technology. The microphones are tested on a number of key parameters for measurement microphones: sensitivity, noise level, frequency response, and immunity to disturbing environmental parameters, such as temperature changes, humidity, static pressure variations, and vibration. A sensitivity of 22 mV/Pa (-33 dB re. 1 V/Pa), and a noise level of 23 dB(A) were measured. The noise level is 7 dB lower than state-of-the-art 1/4-inch measurement microphones. A good uniformity on sensitivity and frequency response has been measured. The sensitivity to temperature changes, humidity, static pressure variations and vibrations is fully comparable to the traditional measurement microphones. This paper shows that high-quality measurement microphones can be made using MEMS technology, with a superior noise performance.     

某民用直升机舱内噪声水平仿真分析研究

声学仿真分析是进行直升机舱内降噪设计的有效技术手段,良好的降噪设计有利于提升民用直升机的市场竞争力。结合试验数据和统计能量法分析了某民用直升机的舱内噪声源贡献度,进而采用声学边界元法分析了该型机的舱内噪声水平。研究表明,该型机舱内主要噪声源为：主减振动、发动机振动、主减空间辐射声、发动机空间辐射声和油箱舱空间辐射声,在无内饰状态下人耳敏感频率范围内的舱内场点噪声为129 dB,蒙皮、整流罩和挡板是影响舱内噪声水平的关键结构,在考虑内饰材料后,场点噪声最大可下降5 dB。该分析思路可以为直升机舱内降噪设计提供技术支持。     

应用于北斗卫星通信系统的低噪声放大器设计

北斗卫星导航系统由我国自主研发,其研制目的是为了在日益严峻的世界环境下巩固我国的军事实力。北斗射频接收芯片是北斗卫星导航系统中整个地面端设备的核心,因此,关于射频接收机芯片的研发工作具有十分重要且实际的意义。文中在基于窄带低噪声放大器理论的基础上,采用TSMC0．18μmCMOS工艺设计了一种应用于北斗通信系统中的低噪声放大器。放大器采用改进的单转双电路结构,并通过缓冲级电路对差分信号的幅度和相位偏差进行了有效的校正。实验结果表明该电路在2．45GHz-2．55GHz频带内输入回波损耗小于-28dB,噪声系数小于1．1dB,功率增益大于15dB,电压增益高于32dB。     

Direct estimation of noisy sinusoids using abductive networks

Spectral estimation techniques have been used for many years. In many cases, their complexity warrants investigating machine-learning alternatives where intensive computations are required only during training, with actual estimation simplified and speeded up. This allows using simple portable apparatus for fast and automated estimation in real time. We propose using abductive network machine learning for estimating both the amplitude and frequency of a single sine wave in the presence of additive Gaussian noise. Models synthesized by training on 1000 representative simulated sinusoids were evaluated on 500 new cases. With no phase variations and a signal to noise ratio of 7 dB, average absolute percentage errors for the sinusoid amplitude and period are 8.4% and 3.6%, respectively. Effects of the range of frequency variations and the noise level on the complexity and accuracy of the models were investigated. Amplitude and period estimates show signs of bias at a signal to noise ratio of 3 dB. Error variances track the Cramer-Rao bounds at high noise levels, with no thresholding observed down to 0 dB. The method is compared with a neural network model and with conventional discrete Fourier transform (DFT) based techniques and a Prony's based approach. The new approach is particularly useful when only a small portion of the sinusoid cycle is measured.     

3～5GHz超宽带可变增益CMOS低噪声放大器的设计

基于TSMC 0.18μm RF CMOS工艺,设计了一款工作在3 GHz～5 GHz的增益连续可调CMOS低噪声放大器。采用RC电阻负反馈式结构以获得良好的输入匹配和噪声性能。通过改变第二级MOS管的偏流,在工作频段内获得了36.5 dB的连续增益可调。     

Burned area forecasting using past burned area records and Southern Oscillation Index for tropical Africa (1981-1999)

An 18-year time series of monthly NOAA-AVHRR Pathfinder Land burned area was analyzed for the region of tropical Africa, from July 1981 to June 1999. The transition period between NOAA-11 and NOAA-14 platforms from July 1993 to June 1995 was not included due to missing and outlier data. Stability of the time series was addressed for the input variables in the burned area algorithm, reflectance and temperature channels.A Seasonal AutoRegressive Integrated Moving-Average (SARIMA) model was developed for forecasting potential burned area. The SARIMA model identified an autoregressive regular term with 1-month lag and an autoregressive 12-month seasonal term with one season (12 months) component. A cross-correlation between Southern Oscillation Index (SOI) and burned area was statistically significant predictor variable in a time series with 20-month lag. Results show that the SARIMA model with this predictor improved both, fitting and forecasting, residual variance, by 4.1% and 5.6%, respectively, thereby, demonstrating potential relationship between SOI and burned area for the study region. Forecasting was estimated by considering only the first 16 years of the monthly burned area in the time series, from July 1981 to June 1997. The prediction for the following 24 months (from July 1997 to June 1999) was within the 95% confidence level indicating that the forecast was a valid characterization of the modeled process.     

TPF: a dynamic system thrashing protection facility

Operating system designers attempt to keep high CPU utilization by maintaining an optimal multiprogramming level (MPL). Although running more processes makes it less likely to leave the CPU idle, too many processes adversely incur serious memory competition, and even introduce thrashing, which eventually lowers CPU utilization. A common practice to address the problem is to lower the MPL with the aid of process swapping out/in operations. This approach is expensive and is only used when the system begins serious thrashing. The objective of our study is to provide highly responsive and cost‐effective thrashing protection by adaptively conducting priority page replacement in a timely manner. We have designed a dynamic system Thrashing Protection Facility (TPF) in the system kernel. Once TPF detects system thrashing, one of the active processes will be identified for protection. The identified process will have a short period of privilege in which it does not contribute its least recently used (LRU) pages for removal so that the process can quickly establish its working set, improving the CPU utilization. With the support of TPF, thrashing can be eliminated in its early stage by adaptive page replacement, so that process swapping will be avoided or delayed until it is truly necessary. We have implemented TPF in a current and representative Linux kernel running on an Intel Pentium machine. Compared with the original Linux page replacement, we showthat TPF consistently and significantly reduces page faults and the execution time of each individual job in several groups of interacting SPEC CPU2000 programs. We also show that TPF introduces little additional overhead to program executions, and its implementation in Linux (or Unix) systems is straightforward. Copyright © 2002 John Wiley & Sons, Ltd.     

An investigation on major physical hazard exposures and health effects of forestry vehicle operators performing wood logging processes

Forest vehicle operators are occupationally exposed to combined hazards such as noise, whole-body vibration(WBV), adverse microclimate, and carbon monoxide. Such combined exposures may not only increase the risk of accidents but they may also have some synergized effects on the developments of major occupational diseases of the workers, which have been among the major concerns of the occupational safety and health for the forestry sector in Romania. This study investigated the combined exposures through measuring and analyzing the equivalent acoustic level LAeq (dB(A)), whole-body vibration (A(8)-value), working microclimate, and carbon monoxide inside the worker's cabin in the breathable area. The vehicles considered in this study included skidding vehicles dedicated to wood exploitation (type I) and agricultural tractors modified for logging (type II). The cumulative distribution function of each types of exposure was calculated in the analyses. This study found that the noise and WBV exposures had large probabilities of exceeding the permissible limits: for noise, 75% for vehicle type I, and 55% for vehicle type II; for the WBV, 63% for type I vehicles, and 72% for type II vehicles. The measured data suggest that the microclimate and carbon monoxide exposures were within their limits in the process of collecting wood. This study also found that 27% of workers participated in the study were detected with occupational diseases. Based on these findings, some intervention methods were recommended to control the exposures and health effects.     

The acoustic startle response and disruption of aiming: I. Effect of stimulus repetition, intensity, and intensity changes

Three experiments examined the disruption of perceptual motor performance by intense noise bursts. Subjects aimed a rifle at a fixed target for 15-s periods separated by 15 s of rest. This cycle was repeated 30 times in each of two series separated by a 15-min rest, each series containing five noise bursts. The noise bursts disrupted aiming for 1-2 s, an effect that increased with sound pressure level for 110, 120, and 130 dB stimuli. There was no difference between stimuli with energy centered on 250 Hz as opposed to 800 Hz. The effect diminished over the five bursts within the first series (but not to zero) and did not recover in the 15-min rest period. Some subjects received three days of testing; in these cases the effect of the noise bursts partially recovered after rest intervals of 24 hrs and then seven days. Other subjects received 15 trials with 110-dB stimuli, then five more trials with 130-dB stimuli. The disruption of aiming by 130 dB stimuli was not reduced by prior exposure to 110-dB stimuli.     

Applying signal detection theory to determine the ringtone volume of a mobile phone under ambient noise

Although technologies for automatically adjusting the volume of mobile phone ringtones according to the ambient noise level have been developed, few studies have investigated the volume (dB) of the ringtone. This study suggested design recommendations for the ringtone volume under loud ambient noise. Based on signal detection theory, two-alternative forced-choice tracking was performed by thirty subjects to obtain hearing thresholds under noisy conditions. Six experimental conditions were examined: all combination of three pure tone frequencies (500 Hz, 1000 Hz, 4000 Hz) and two white noise levels (70 dB, 80 dB). The results showed that the ringtone volume should increase by 10–15 dB on average when the noise level increases from 70 dB to 80 dB. When adjusting the volume according to the ambient noise level, the volume should be changed differently according to the frequencies of a ringtone. The ringtone should be composed of low-frequency sounds under loud ambient noise because the subjects were very sensitive to the pure tone with frequency of 500 Hz. The results of this study could be used when developing design guidelines for the adaptive ringtone of a mobile phone. Moreover, designers can use this method to design other auditory signals such as notification and emergency alarms that have different chances of signal detectability.Relevance to industryThe results of this study may provide useful information to designers who consider the volume and frequency of a ringtone when adjusting ringtone volume according to ambient noise level. Moreover, the method used in the study could also be widely used to design auditory signals of mobile devices other than mobile phones.