Nonoccupational noise: exposures associated with routine activities

Efforts to characterize nonoccupational noise exposures have focused primarily on infrequent, episodic events. Few studies have assessed noise levels resulting from routine daily activities. In the current study, 112 construction workers wore datalogging noise dosimeters and simultaneously completed activity logs during two phases of data collection. The 81 subjects monitored in phase 1 received logs listing numerous preselected occupational and nonoccupational activities, while the 31 subjects monitored in phase 2 used free-field logs and reported nonoccupational activities in greater detail. Nearly all of the 221,439 1-min intervals of nonoccupational L(eq) level and activity reporting were below 70 dBA; only a small percentage exceeded 80 dBA. The primary contributor to nonoccupational noise exposure was traveling in a car or bus, while time at home contributed the least. One hundred seventy 24-h L(eq) levels were computed from the 1-min noise level data. The percentage of phase 2 workday L(eq(24)) levels which exceeded 80 dBA was higher than that of the nonworkday levels. The mean L(eq(24)) level of phase 2 workdays was higher than that of nonworkdays, and the difference was statistically significant. Routine nonoccupational noise exposures contributed much less to total noise dose than occupational exposures in the subjects evaluated.     

A threatened beluga (Delphinapterus leucas) population in the traffic lane: vessel-generated noise characteristics of the Saguenay-St. Lawrence Marine Park, Canada

The threatened resident beluga population of the St. Lawrence Estuary shares the Saguenay-St. Lawrence Marine Park with significant anthropogenic noise sources, including marine commercial traffic and a well-established, vessel-based whale-watching industry. Frequency-dependent (FD) weighting was used to approximate beluga hearing sensitivity to determine how noise exposure varied in time and space at six sites of high beluga summer residency. The relative contribution of each source to acoustic habitat degradation was estimated by measuring noise levels throughout the summer and noise signatures of typical vessel classes with respect to traffic volume and sound propagation characteristics. Rigid-hulled inflatable boats were the dominant noise source with respect to estimated beluga hearing sensitivity in the studied habitats due to their high occurrence and proximity, high correlation with site-specific FD-weighted sound levels, and the dominance of mid-frequencies (0.3-23 kHz) in their noise signatures. Median C-weighted sound pressure level (SPL(RMS)) had a range of 19 dB re 1 μPa between the noisiest and quietest sites. Broadband SPL(RMS) exceeded 120 dB re 1 μPa 8-32% of the time depending on the site. Impacts of these noise levels on St. Lawrence beluga will depend on exposure recurrence and individual responsiveness.     

交通噪声对中小学生课堂行为的影响

一些调查结果表明,城市中的中小学校受环境噪声的干扰严重,尤其是交通噪声。我们对不同噪声级(40至70dBA)下学生课堂行为作了一系列的心理学实验,和汉语清晰度测验。所得结果经单因子方差分析和t检验来考核(用高级统计软件RDAS)不同结果之间差异的显著性,从而可得出当噪声级L_eq超过50dBA,或是L₁₀>55dBA,L₅₀>50dBA时,学生课堂行为会出现显著性差异(P<0.05)。另外还利用RBAS软件进行了皮尔逊(简单)相关分析,了解到上述心理学实验各作业指标之间的相关性并不很大,说明大部分作业不能相互替代,选择这些作业是必要的。本研究结果表明,教室内最大容许噪声级定为L₁₀=55dBA,L₅₀=50dBA是合适的。     

Improvement of Zwicker’s psychoacoustic annoyance model aiming at tonal noises

According to 4 acoustical parameters of noise samples (i.e., loudness, sharpness, fluctuation strength and roughness), Zwicker’s psychoacoustic annoyance model can be used to estimate the relative degree of noise annoyance. However, this model cannot be well applied to compare the annoyance degrees of tonal noises and atonal noises. In order to improve its estimation effect on tonal noises, 3 groups of noise samples were selected randomly, i.e., 27 low-frequency tonal noise samples induced by a 1000 kV transformer with A-weighted equivalent sound pressure levels ranging from 41.2 dBA to 73.0 dBA; 30 low-, mid- or high-frequency tonal/atonal noise samples with loudness levels ranging from 60 phon to 80 phon; and 60 other noise samples with A-weighted equivalent sound pressure levels ranging from 40.7 dBA to 75.0 dBA. Laboratory listening tests were conducted on the above 3 sample groups respectively via an 11-point numerical scale. The Zwicker’s psychoacoustic annoyance model was improved by taking tonality into account, and introducing the evaluation result of the first noise sample group (1000 kV transformer noise samples) to determine the coefficients in the model. The applicability of the improved model was examined by the evaluation results of the other two groups as well as the data in a previous research on annoyance of 220 kV/500 kV transformer noises. Results show that the improved model can estimate the relative annoyance degrees caused by various types of tonal/atonal noises much more accurately.     

Evaluating the maximum playback sound levels from portable digital audio players

To assess the maximum sound levels that may be experienced by young people in Canada from modern digital audio players, this study measured nine recent models of players and 20 earphones. Measurement methodology followed European standard BS EN 50332. Playback levels ranged from 101 to 107 dBA at maximum volume level. Estimated listener sound levels could vary from 79 to 125 dBA due to the following factors: (i) earphone seal against the ear, (ii) player output voltage, (iii) earphone sensitivity, and (iv) recorded music levels. There was a greater potential for high sound levels if intra-concha "earbud" earphones were used due to the effect of earphone seal. Simpler measurement techniques were explored as field test methods; the best results were obtained by sealing the microphone of a sound level meter to the earphone using a cupped hand and correcting for the free field response of the ear. Measurement of noise levels 0.25 m from the earphone showed that a bystander is unlikely to accurately judge listener sound levels.     

Underwater temporary threshold shift in pinnipeds: effects of noise level and duration

Behavioral psychophysical techniques were used to evaluate the residual effects of underwater noise on the hearing sensitivity of three pinnipeds: a California sea lion (Zalophus californianus), a harbor seal (Phoca vitulina), and a northern elephant seal (Mirounga angustirostris). Temporary threshold shift (TTS), defined as the difference between auditory thresholds obtained before and after noise exposure, was assessed. The subjects were exposed to octave-band noise centered at 2500 Hz at two sound pressure levels: 80 and 95 dB SL (re: auditory threshold at 2500 Hz). Noise exposure durations were 22, 25, and 50 min. Threshold shifts were assessed at 2500 and 3530 Hz. Mean threshold shifts ranged from 2.9-12.2 dB. Full recovery of auditory sensitivity occurred within 24 h of noise exposure. Control sequences, comprising sham noise exposures, did not result in significant mean threshold shifts for any subject. Threshold shift magnitudes increased with increasing noise sound exposure level (SEL) for two of the three subjects. The results underscore the importance of including sound exposure metrics (incorporating sound pressure level and exposure duration) in order to fully assess the effects of noise on marine mammal hearing.     

Temporary threshold shift in human subject exposed to noise

Using an audiometer,the effect of the noise level upon temporarythreshold shift(TTS)for five trained normal subjects(left ear only)was studied.The measurements were carried out after 6 min exposure(in third octave band)for different sound pressure levels ranging between 75-105 dB at three test fre-quencies 2,3,and 4 kHz.The results indicated that at exposure to noise of soundpressure level(SPL)above 85 dB,TTS increases linearly with ths SPL for all thetest frequencies.The work had extended to study the recovery curves for the sameears.The results indicated that the reduction in TTS on doubling the recoverytimes,for the two sound pressure levels 95 dB and 105 dB,occurs at a rate of near-ly 3 dB.The comparison of the recovery curve at 3 kHz with that calculated usingWard's general equation for recovery was made.Finally,to study the values ofTTS produced by exposure to certain noise at different test frequencies,distribu-tion curves for two recovery times were plotted representing TTS values,for anexposure     

Making MRI quieter

We have mitigated acoustic noise in a 1.5 T cylindrical MRI scanner equipped with epoxy-potted, shielded gradients. It has been widely assumed that MRI acoustic noise comes overwhelmingly from vibrations of the gradient assembly. However, with vibration-isolated gradients contained in an airtight enclosure, we found the primary sources of acoustic noise to be eddy-current-induced vibrations of metal structures such as the cryostat inner bore and the rf body coil. We have elucidated the relative strengths of source-pathways of acoustic noise and assembled a reduced-acoustic-noise demonstration MRI system. This scanner employed a number of acoustic noise reduction measures including a vacuum enclosure of a vibrationally isolated gradient assembly, a low-eddy-current rf coil and a non-conducting inner bore cryostat. The demonstration scanner reduced, by about 20 dBA, the acoustic noise levels in the patient bore to 85 dBA and below for several typical noisy pulse sequences. The noise level standing near the patient bore is 71 dBA and below. We have applied Statistical Energy Analysis to develop a vibroacoustic model of the MR system. Our model includes vibrational sources and acoustic pathways to predict acoustic noise and provides a good spectral match above 400 Hz to experimentally measured sound levels. This tool enables us to factor acoustics into the design parameters of new MRI systems.     

Vocal Behavior and Vocal Loading Factors for Preschool Teachers at Work Studied with Binaural DAT Recordings

Preschool teachers are at risk for developing voice problems such as vocal fatigue and vocal nodules. The purpose of this report was to study preschool teachers' voice use during work. Ten healthy female preschool teachers working at daycare centers (DCC) served as subjects. A binaural recording technique was used. Two microphones were placed on both sides of the subject's head, at equal distance from the mouth, and a portable DAT recorder was attached to the subject's waist. Recordings were made of a standard reading passage before work (baseline) and of spontaneous speech during work. The recording technique allowed separate analyses of the level of the background noise, and of the subjects' voice sound pressure level, mean fundamental frequency, and total phonation time. Among the results, mean background noise level for the ten DCCs was 76.1 dBA (range 73.0-78.2), which is more than 20 dB higher than what is recommended where speech communication is important (50-55 dBA). The subjects spoke on an average of 9.1 dB louder (p < 0.0001), and with higher mean fundamental frequency (247 Hz) during work as compared to the baseline (202 Hz) (p < 0.0001). Mean phonation time for the group was 17%, which was considered high. It was concluded that preschool teachers do have a highly vocally demanding profession. Important steps to reduce the vocal loading for this occupation would be to decrease the background noise levels and include pauses so that preschool teachers can rest their voices.     

Reducing Occupational Noise Propagated from Centrifugal Fan through Dissipative Silencers: A Field Study

Acoustic performance of dissipative silencer was evaluated to determine the effectiveness of perforated duct porosity and absorbent material density in reducing occupational noise exposure propagated from centrifugal fan. Design charts were applied to predict noise reduction and length of a dissipative silencer. Dissipative silencers with various punched duct porosity (14%, 30% and 40%) and sound absorbent density (80 Kg/m³, 120 Kg/m³, and 140 Kg/m³) were designed and fabricated. According to ISO9612 and ISO11820, noise level was measured before and after installing all nine test silencers at fixed workstations around the discharge side of a centrifugal fan in a manufacturing plant. On average, the noise level at the discharge side of a fan without silencer was measured to be 93.6 dBA, whereas it was significantly mitigated by 67.4 dBA to 70.1 dBA after installing all silencers. Dynamic insertion loss for a dissipative silencer with 100 cm length was predicted to be 27.9 dB, which was in agreement with experimental ones. Although, there was no significant differences between insertion loss of silencers, the one with 30% porosity and 120 Kg/m³ rock wool density had the highest insertion loss of 26.2 dBA. Dissipative silencers noticeably reduced centrifugal fan noise exposures. Increasing sound absorbent density and duct porosity up to a certain limit could probably be effective in noise reduction of dissipative silencers.     

The Okinawa study: an estimation of noise-induced hearing loss on the basis of the records of aircraft noise exposure around Kadena Air Base

Aircraft noise measurements were recorded at the residential areas in the vicinity of Kadena Air Base, Okinawa in 1968 and 1972 at the time of the Vietnam war. The estimated equivalent continuous A-weighted sound pressure level L_Aeq for 24 h was 85 dB.The time history of sound level during 24 h was estimated from the measurement conducted in 1968, and the sound level was converted into the spectrum level at the centre frequency of the critical band of temporary threshold shift (TTS) using the results of spectrum analysis of aircraft noise operated at the airfield. With the information of spectrum level and its time history, TTS was calculated as a function of time and level change. The permanent threshold shift was also calculated by means of Robinson's method and ISO's method. The results indicate the noise exposure around Kadena Air Base was hazardous to hearing and is likely to have caused hearing loss to people living in its vicinity.     

A road traffic noise pattern simulation model that includes distributions of vehicle sound power levels

Annoyance, sleep disturbance and other health effects of road traffic noise exposure may be related to both level and number of noise events caused by traffic, not just to energy equivalent measures of exposure. Dynamic traffic noise prediction models that include instantaneous vehicle noise emissions can be used to estimate either of these measures. However, current state-of-the-art vehicle noise emission models typically consider a single emission law for each vehicle category, whereas measurements show that the variation in noise emission between vehicles within the same category can be considerable. It is essential that the influence of vehicles that are producing significantly more (or less) noise than the average vehicle are taken into account in modeling in order to correctly predict the levels and frequency of occurrence of road traffic noise events, and in particular to calculate indicators that characterize these noise events. Here, an approach for predicting instantaneous sound levels caused by road traffic is presented, which takes into account measured distributions of sound power levels produced by individual vehicles. For the setting of a receiver adjacent to a dual-lane road carrying free flow traffic, the effect of this approach on estimated percentile levels and sound event indicators is investigated.     

Noise-impact estimates per FTA and APTA criteria

In a recent paper, light-rail line noise exposures were predicted both in terms of maximum pass-by sound levels for comparison to APTA criteria and day-night average sound levels for comparison to FTA criteria. For the local land uses and ambient noise conditions of the project, the distances for the unmitigated pass-by noise exposures to attenuate to the APTA and FTA criteria limits were estimated and the numbers of included dwellings counted. The results found that the FTA impact-onset (i.e., “some-impact”) criterion curve yielded significantly greater noise exposed areas while the APTA criteria yielded results between those of the FTA “some”- and “severe”-impact curves. However, those results only applied to the specific project under evaluation. This paper attempts to extend and generalize the comparison by parametric computation of exposed areas using both the FTA and APTA procedures. Predicted exposures in this paper are compared as a function of background ambient sound levels, type of land use impacted, numbers of daytime and nighttime operations, and train pass-by maximum sound levels. At very low background ambient sound levels, FTA tended to predict the greatest exposure, while in very noisy environments, APTA predicted more exposure. APTA predicted more exposure with low numbers of daily and/or nighttime operations, and FTA predicted more exposure with high numbers, but the comparative exposures were strongly dependent upon background ambient sound level and land use. For train pass-by maximum sound levels, APTA tended to show more exposure for very quiet pass-bys and to be intermediate to FTA/some and FTA/severe for noisier events—with the comparative exposures strongly dependent upon background ambient and land use.     

粉碎机的噪声降低

粉碎机噪声,属于撞击性机械噪声源。本文对常用的一种粉碎机进行了系统地噪声和振动分析,结果证明,粉碎机高达118 dBA的噪声,主要由于高速旋转的钢齿撞击声以空气声形式通过开口辐射产生的,机壳的振动和固体传声不起重要作用。采用开口式消声器处理后,噪声已由118dBA降低到80 dBA。这个例子可以表明,噪声控制一定要对具体噪声作具体分析,有针对性地采取措施,即使粉碎机一类的撞击性机械声源,也能有效地进行控制。     

Hearing loss from gun and railroad noise--relations with ISO standard 1999.

Pure-tone hearing thresholds and anamnestic data pertaining to nosocusis and exposure to gun noise were analyzed for 9778 male railroad train-crew workers. A major portion of losses in hearing sensitivity due to railroad noise are obscured in comparisons of hearing levels of trainmen with the hearing levels of the unscreened samples of United States males given in Annex B, ISO 1999 [ISO 1999 (1990), "Acoustics--Determination of occupational noise exposure and estimation of noise-induced hearing impairment" (International Organization for Standardization, Geneva)]. Comparisons of the hearing levels, adjusted for nosocusis, of trainmen who had used no guns, with the hearing levels of otologically and noise screened males (Annex A, ISO 1999) reveal significant losses due to railroad noise. Additional losses were found at high frequencies in trainmen who had used guns. It appears that the effective Leq8h exposure level of trainmen to railroad noise is about 92 dBA, and 87-89 dBA to gun noise. These results are in general agreement with those of study of railway workers by Prosser et al. [Br. J. Audiol. 22, 85-91 (1988)]. Asymmetries in losses between the two ears, effects of ear protection, losses from nosocusis, and losses from sport, as compared to military, gun noise exposures, are examined.     

Loud Speech in Realistic Environmental Noise: Phonetogram Data, Perceptual Voice Quality, Subjective Ratings, and Gender Differences in Healthy Speakers

A new method for cancelling background noise from running speech was used to study voice production during realistic environmental noise exposure. Normal subjects, 12 women and 11 men, read a text in five conditions: quiet, soft continuous noise (75 dBA to 70 dBA), day-care babble (74 dBA), disco (87 dBA), and loud continuous noise (78 dBA to 85 dBA). The noise was presented over loudspeakers and then removed from the recordings in an off-line processing operation. The voice signals were analyzed acoustically with an automatic phonetograph and perceptually by four expert listeners. Subjective data were collected after each vocal loading task. The perceptual parameters press, instability, and roughness increased significantly as an effect of speaking loudly over noise, whereas vocal fry decreased. Having to make oneself heard over noise resulted in higher SPL and F0, as expected, and in higher phonation time. The total reading time was slightly longer in continuous noise than in intermittent noise. The women had 4 dB lower voice SPL overall and increased their phonation time more in noise than did the men. Subjectively, women reported less success making themselves heard and higher effort. The results support the contention that female voices are more vulnerable to vocal loading in background noise.     

The relationship between traffic noise and insomnia among adult Japanese women

To clarify the relationship between traffic noise and insomnia, the authors conducted a survey and measured the actual sound level of noise in an urban area. Questionnaires were distributed to adult women who lived within 150 m from two major roads and were completed by 648 of the 1286 subjects (50.4%). The area was divided into three zones according to distance from the road (more than 50, 20-50 and 0-19.9 m). Fifty-seven subjects (8.8%) were classified as having insomnia. Average values of sound level at distances of 20, 50, and 100 m from the major road were L_eq 64.7, 57.1, and 51.8 dBA, respectively. Overall, there were no significant differences among the three zones in the prevalence of insomnia and no association between distance from the road and insomnia. However, the result from a sub-data set of the subjects who lived in the areas that showed decreasing noise level as the distance from the main road increased showed that distance from the road was associated with insomnia. This study suggests that researchers should consider the actual traffic situation and its sound level in epidemiological studies about the effects of traffic noise on insomnia.     

Is it necessary to penalize impulsive noise +5 dB due to higher risk of hearing damage?

It is studied whether the +5 dB penalty for impulsiveness established by ISO 1999:1990 accounts for a higher risk of noise-induced hearing loss. A total of 16 normal-hearing human subjects were exposed for 10 min to two types of binaural industrial-recordings: (1) a continuous broad-band noise normalized to L(EX,8 h)=80 dBA and (2) the combination of the previous stimulus with an impulsive noise normalized to L(EX,8 h)=75+5(db penalty)=80 dBA (peak level 117 dBC and repetition rate of 0.5 impacts per second). Distortion product otoacoustic emissions (DPOAEs) were measured in a broad frequency range before and in the following 90 min after the exposure. The group results show that the continuous exposure had a bigger impact on DPOAE levels, with a maximum DPOAE shift of approximately 5 dB in the frequency range of 2-3.15 kHz during the first 10 min of the recovery. No evident DPOAE shift is seen for the impulsive + continuous stimulus. The results indicate that the penalty overestimated the effects on DPOAE levels and support the concept that the risk of hearing loss from low-level impulses may be predicted on an equal-energy basis.