A-weighted Sound Pressure Level Research Articles

Objective quantification of perceived differences between measured and synthesized aircraft sounds

This paper presents an approach with which perceived audible differences in aircraft sounds can be quantified and presented in an objective manner. The objective quantification of the subjectively heard audible differences is intended to serve two primary goals. It can firstly enable developers of auralization technology to make the auralized sounds more realistic by identifying in which aspects the synthesized sounds differ from their real-life counterparts and to what extent. The quantification can secondly provide an improved and more detailed means of distinguishing between aircraft sounds in general, beyond the conventional metrics of A-weighted Sound Pressure level (dBA) or Effective Perceived Noise Level (EPNL) used currently to assess aircraft noise. In this study sound quality metrics are used to quantify the differences in aircraft sounds. These metrics are widely used in other industries such as the automotive sector. Audio files of a reference aircraft, made over identical flight paths at a noise monitoring station in the vicinity of Schiphol airport, are compared in terms of both conventional and sound quality metrics for four measured and four auralized audio files. It is observed from the comparison that differences that may appear small in the conventional metrics can be significant in terms of the sound quality metrics. Significant differences in measured and synthesized sounds are observed for the aircraft considered in this study with regards to the tonal content and fluctuations in amplitude that occur over time. The conventional metrics are seen to capture the overall loudness aspect of aircraft sounds, but give no clear information regarding which spectral or temporal characteristics cause the sounds to be perceived as audibly different.

Propagation characteristics of audible noise generated by single corona source under positive DC voltage

The directivity and lateral profile of corona-generated audible noise (AN) from a single corona source are measured through experiments carried out in the semi-anechoic laboratory. The experimental results show that the waveform of corona-generated AN consists of a series of random sound pressure pulses whose pulse amplitudes decrease with the increase of measurement distance. A single corona source can be regarded as a non-directional AN source, and the A-weighted SPL (sound pressure level) decreases 6 dB(A) as doubling the measurement distance. Then, qualitative explanations for the rationality of treating the single corona source as a point source are given on the basis of the Ingard’s theory for sound generation in corona discharge. Furthermore, we take into consideration of the ground reflection and the air attenuation to reconstruct the propagation features of AN from the single corona source. The calculated results agree with the measurement well, which validates the propagation model. Finally, the influence of the ground reflection on the SPL is presented in the paper.

Influences of low-frequency and other noises produced by wind turbines: An epidemiological literature review.

Objectives Due to its' environment-friendly and clean energy characteristics, wind power has been increasingly used globally, particularly in advanced countries. However, concerns about health hazards, especially due to low-frequency and other noises generated from wind turbines, have been reported repeatedly. In order to manage adverse health effects appropriately, regulatory standards or guidelines that consider the health of residents need to be developed. To provide a scientific basis for the development of such regulatory standards and guidelines, this paper conducted a literature review to analyze epidemiological studies involving residents living in the vicinity of wind farms.Methods Using the PubMED database, epidemiological papers that examined the health effects of noises produced by wind turbines were searched and collected. Additional papers were collected from the abstracts presented at relevant international academic conferences such as the Inter-Noise 2013 and Wind Turbine Noise 2015. An evidence table comprising the study design, subjects, exposure assessment, outcomes, confounders, and research results of each selected study was created.Results A total of 11 papers were collected (2 of which were abstracts from the international academic conferences). These studies reported outcomes such as perception of noises, annoyance caused by the noises, and the association of the noises with stress and sleeplessness. Significant associations between the noises or annoyance produced by wind turbines and subjective adverse health effects were reported repeatedly. Two studies reported an odds ratio of 1.1 for an increase of 1 dB in the A-weighted sound pressure level as a factor representing the influence level. For other factors, it was not possible to compare the magnitude of the impact among the collected studies. Individual attitudes toward wind power and landscapes, economic benefits of wind farms, visibility of wind turbines, sensitivity to sounds, and concerns over health hazards were reported as confounders.Conclusion Significant associations between the noises or annoyance produced by wind turbines and subjective adverse health effects were reported repeatedly. However, there was insufficient evidence to conclude whether the annoyance was caused by the psychological response to the construction of wind farms or by the actual exposure to noises generated by wind farms.

Spatial and temporal determinants of A-weighted and frequency specific sound levels—An elastic net approach

BackgroundUrban sound levels are a ubiquitous environmental stressor and have been shown to be associated with a wide variety of health outcomes. While much is known about the predictors of A-weighted sound pressure levels in the urban environment, far less is known about other frequencies. ObjectiveTo develop a series of spatial-temporal sound models to predict A-weighted sound pressure levels, low, mid, and high frequency sound for Boston, Massachusetts. MethodsShort-term sound levels were gathered at n = 400 sites from February 2015 – February 2016. Spatial and meteorological attributes at or near the sound monitoring site were obtained using publicly available data and a portable weather station. An elastic net variable selection technique was used to select predictors of A-weighted, low, mid, and high frequency sound. ResultsThe final models for low, mid, high, and A-weighted sound levels explained 59 – 69% of the variability in each measure. Similar to other A-weighted models, our sound models included transportation related variables such as length of roads and bus lines in the surrounding area; distance to road and rail lines; traffic volume, vehicle mix, residential and commercial land use. However, frequency specific models highlighted additional predictors not included in the A-weighted model including temperature, vegetation, impervious surfaces, vehicle mix, and density of entertainment establishments and restaurants. ConclusionsBuilding spatial temporal models to characterize sound levels across the frequency spectrum using an elastic net approach can be a promising tool for noise exposure assessments within the urban soundscape. Models of sound's character may give us additional important sound exposure metrics to be utilized in epidemiological studies.

Sound quality evaluation of high-speed train interior noise by adaptive Moore loudness algorithm

An online experiment to acquire the interior noise of a China Railways High-speed (CRH) train showed that it was mainly composed of middle-low frequency components and could not be described properly by linear or A-weighted sound pressure level (SPL). Thus, the appropriate way to evaluate the high-speed train interior noise is to use sound quality parameters, and the most important is loudness. To overcome the disadvantages of the existing loudness algorithms, a novel signal-adaptive Moore loudness algorithm (AMLA) based on the equivalent rectangular bandwidth (ERB) spectrum was introduced. The validation reveals that AMLA can obtain higher accuracy and efficiency, and the simulated dark red noise conforms best to the high-speed train interior noise by loudness and auditory assessment. The main loudness component of the interior noise is below 27.6 ERB rate (erbr), and the sound quality of the interior noise is relatively stable between 300–350 km/h. The specific loudness components among 12–15 erbr stay invariable throughout the acceleration or deceleration process while components among 20–27 erbr are evidently speed related. The unusual random noise is effectively identified, which indicates that AMLA is an appropriate method for sound quality assessment of the high-speed train under both steady and transient conditions.

Surface aging effects of long-term energized conductors on spectrum characteristics of audible noise

The impact of surface aging level of long-term energized conductors on spectrum characteristics of audible noise is studied in this paper. It is found that the average roughness and root-mean-square roughness of conductors increase with the operating time, namely the aging degree, through the quantitative measurement. A-weighted equivalent continuous sound pressure level (LAeq) is found to increase with the aging level. As the aging aggravation, the LAeq and its high-frequency components (>1 kHz) increase substantially and high-frequency components are mainly contributing to the increasing of LAeq. The high-frequency components (>1 kHz) of the new and aged stranded conductors have a marked increasing trend as the surface potential gradient increases, while the low-frequency components are mainly environment noise.

Improved vehicle interior structure-borne noise induced by the powertrain using parallel dry friction damper

Because of the higher requirements for vehicle comfort and people’s increasing ecological consciousness, research on the interior noise in a vehicle has received wide attention, among which structure-borne noise is hard to diagnose. To solve the problem, the transfer path analysis method of powertrain structure-borne noise has been systematically analyzed. By introduction of the powertrain source-path-receiver model, this method enables the researchers to estimate and study the noise, vibration, and harshness transfer functions and their operational forces. The aim is to further improve noise, vibration, and harshness with minimal negative impact on other vehicle attributes, such as ride comfort, handling, drivability, durability, etc. In this article, a parallel dry friction damper was added to the vehicle nearside powertrain mount, which is the most significant one to the receiver of passenger vehicle for improving its interior structure-borne noise induced by the engine. The test vehicle was a midsize executive vehicle. Since the structure-borne noise is composed of multiple paths, then the transfer path analysis test of the vehicle was carried out, and the transfer function and operational data at speed range started from 20 to 100 km/h were obtained. On the basis of the transfer path analysis results and the above principle, the friction damper on the body side of the nearside mount is improved by combination of the experimental transfer path analysis and the final measurements. The results indicate that a significant reduction for the A-weighted sound pressure level of the interior noise has been gained when the frictional damper was added to conventional mount.

Short-term association between personal exposure to noise and heart rate variability: The RECORD MultiSensor Study

BackgroundStudies revealed long-term associations between noise exposure and cardiovascular health, but the underlying short-term mechanisms remain uncertain. ObjectivesTo explore the concomitant and lagged short-term associations between personal exposure to noise and heart rate variability (HRV) in a real life setting in the Île-de-France region. MethodsThe RECORD MultiSensor Study collected between July 2014 and June 2015 noise and heart rate data for 75 participants, aged 34–74 years, in their living environments for 7 days using a personal dosimeter and electrocardiography (ECG) sensor on the chest. HRV parameters and noise levels were calculated for 5-min windows. Short-term relationships between noise level and log-transformed HRV parameters were assessed using mixed effects models with a random intercept for participants and a temporal autocorrelation structure, adjusted for heart rate, physical activity (accelerometry), and short-term trends. ResultsAn increase by one dB(A) of A-weighted equivalent sound pressure level (Leq) was associated with a 0.97% concomitant increase of the Standard deviation of normal to normal intervals (SDNN) (95% CI: 0.92, 1.02), of 2.08% of the Low frequency band power (LF) (95% CI: 1.97, 2.18), of 1.30% of the High frequency band power (HF) (95% CI: 1.17, 1.43), and of 1.16% of the LF/HF ratio (95% CI: 1.10, 1.23). The analysis of lagged exposures to noise adjusted for the concomitant exposure illustrates the dynamic of recovery of the autonomic nervous system. Non-linear associations were documented with all HRV parameters with the exception of HF. Piecewise regression revealed that the association was almost 6 times stronger below than above 65 Leq dB(A) for the SDNN and LF/HF ratio. ConclusionPersonal noise exposure was found to be related to a concomitant increase of the overall HRV, with evidence of imbalance of the autonomic nervous system towards sympathetic activity, a pathway to increased cardiovascular morbidity and mortality.

Silent navigator-triggered silent MRI of the abdomen.

To develop and demonstrate the feasibility of a silent respiratory navigator technique for prospective triggering, which was incorporated into a three-dimensional radial zero-echo-time sequence for respiratory navigated silent abdominal imaging. A nonselective hard excitation radiofrequency pulse was used for the navigator sequence with a derated readout gradient, to avoid generation of high levels of acoustic noise. The acquired navigator signals were processed in real time and used for prospective triggering of the zero-echo-time sequence. Ten healthy volunteers were scanned using the proposed and conventional techniques at 1.5 T. An acoustic noise measurement with A-weighted continuous equivalent sound pressure level was also performed. The sound pressure-level values of the background noise, zero-echo-time imaging, conventional, and silent navigators were 68.3, 68.4, 102.5, and 69.4 dBA, respectively. Excellent correlation with correlation coefficients greater than 0.9 was observed between the bellows signals and displacement values calculated from the navigators. Sharpness of the portal vein of both conventional and silent navigator-triggered images was significantly higher than those of nontriggered images. The silent navigator-triggered zero-echo-time technique is feasible and might improve image quality and workflow of abdominal MRI of patients who are prone to acoustic noise. Magn Reson Med 79:2170-2175, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

The Hearing Threshold of Employees Exposed to Noise Generated by the Low-Frequency Ultrasonic Welding Devices

Abstract The aim of the study was to assess the hearing threshold levels (HTLs) in employees exposed to noise generated by low-frequency ultrasonic technological equipment in comparison with the HTLs of workers exposed to audible noise at the similar A-weighted equivalent-continuous sound pressure level. The study includes measurements of ultrasonic and audible noise at workplaces and hearing tests, i.e. conventional pure-tone audiometry and extended high-frequency audiometry. The study group comprised 90 workers, aged 41.4±10.0 years (mean±SD), exposed for 17.3±9.8 years to noise generated by ultrasonic devices at mean daily noise exposure level (‹LEX,8h›) of 80.6±2.9 dB. The reference group consists of 156 subjects, exposed to industrial noise (without ultrasonic components) at similar A-weighted equivalent-continuous sound pressure level (‹LEX,8h› = 81.8±2.7 dB), adjusted according to age (39.8±7.7 years), gender and job seniority (14.0±7.0 years). This group was selected from database collected in the Nofer Institute of Occupational Medicine. Audiometric hearing threshold levels in the frequency range of 0.5-6 kHz were similar in both groups, but in the frequency range of 8-12.5 kHz they were higher in the group of employees exposed to ultrasonic noise. The findings suggest that differences in the hearing threshold (at high frequencies) in analyzed groups may be due to differences in spectral composition of noise and show the need to continue the undertaken studies.

Annoyance response and improvement of Zwicker's psychoacoustic annoyance model aiming at tonal noises

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.

A Novel Sound Quality Evaluation Method of the Diagnosis of Abnormal Noise in Interior Permanent-Magnet Synchronous Motors for Electric Vehicles

A novel sound quality (SQ) evaluation method is developed to diagnose abnormal noise of interior permanent-magnet synchronous motors (IPMSM) for electric vehicle (EV). A-weighted sound pressure level (A-W SPL) of noise in IPMSM and six psychoacoustic characteristics, which include sharpness, roughness, loudness, articulation index, tonality, and fluctuation strength, are described through the objective evaluation of SQ. The paired comparison method (PCM) and the grade evaluation method (GEM) are respectively applied in subjective evaluation on relative annoyance and absolute annoyance of IPMSM for EV, and the combined application of these two methods is proposed originally. Finally, the BP neural network model for SQ evaluation of abnormal noise in IPMSM is established, the characteristics, conditions, and influencing factors of abnormal noise are effectively diagnosed. This novel evaluation method effectively solves the problem that the annoyance level is unable to be evaluated through the PCM, and the GEM relies on rich audition experience of evaluation subject. It also improves the accuracy of diagnosis of abnormal noise in IPMSM for EV.

Aerodynamic noise numerical simulation and noise reduction study on automobile alternator

Aerodynamic noise is the predominant component of automobile alternator noise at high speed, which directly affects the noise characteristic and noise control of alternator. Based on Lighthill acoustic theory, the aerodynamic noise of an automobile alternator was simulated with three-dimensional, Large eddy simulation (LES) and Ffowcs Williams-Hawkings (FW-H) acoustic model, and the aerodynamic noise reduction research was conducted through optimizing the front fan blade spacing angle of alternator with vector composition method while considering high fan flow and optimal noise frequency components for reduced harmonic rotating noise of alternator. The results show that the sound pressure amplitude of the primary aerodynamic noise components simulated with LES are in good agreement with experimental ones, and the dominant harmonic frequency components of aerodynamic noise are in the 4th, 6th, 8th, 10th, 12th and 18th orders and the A-weighted sound pressure level of one-third octave mainly concentrates in 1120-7000 Hz. The average total noise level of alternator noise is decreased by 2.58 dB, and the mass flow of monitoring surface of fan blade is increased by 1.36 g/s with 5.80 dB decrease in the sound level of the 12th and 18th harmonic orders on average with optimized front fan blade spacing angles, which verifies the effectiveness of the noise reduction method proposed in this paper.

Sound quality evaluation of air-conditioner noise based on factors of the autocorrelation function

The aim of this paper is to clarify the characteristics of air-conditioner noise and determine the factor that is most influential on the subjective annoyance caused by this noise. The A-weighted equivalent continuous sound pressure level (LAeq) and factors extracted from the autocorrelation function (ACF) were analyzed. Subjective annoyance was evaluated using a paired comparison method. Multiple regression analyses were performed using a linear combination of LAeq, the ACF factors, and their standard deviations (SDs). The results indicated that the noise characteristics caused by each air conditioner and each operating level are determined by LAeq, and by the width of the first decay of the ACF, Wϕ(0), which corresponds to the spectral centroid. The multiple regression analyses indicated that the total subjective annoyance caused by air-conditioner noise can be predicted using the delay time and amplitude of the first maximum peak of the ACF (τ1 and ϕ1) and the SD of ϕ1. Annoyance was found to increase with decreasing τ1 and ϕ1, and with increasing ϕ1 SD, suggesting that noise components with higher pitches, weaker pitch strengths, and larger pitch strength variations cause greater levels of annoyance.

Acoustic behavior prediction for low-frequency sound quality based on finite element method and artificial neural network

In this paper, a hybrid approach called FEM-ANN model is proposed by combining the finite element method (FEM) and artificial neural network (ANN) to predict the acoustic behavior of an auditory system. Based on the scanned point cloud data, the three-dimensional numerical models of the external auditory canal, tympanic membrane and middle ear are established by using the reverse prototyping technology, as are the FEM models. Setting the interior noises of the vehicle as excitations, the assembled FEM model is used to calculate the responses of the stapes footplate. According to the auditory perception characteristics of the human, a modified one-third octave filter bank is designed to calculate the vibration energies of stapes footplate in the critical bands, and thereby an energy-based feature matrix is established. Further, the sound quality (SQ) indices of interior noises, such as A-weighted sound pressure level (SPL), loudness and sharpness are calculated. By considering the extracted feature matrices as inputs and the calculated SQ indices as outputs, a three-layer ANN model with the radial basis function (RBF) is established for mapping the stapes footplate vibration to the human auditory perception. Verifications show that, the simulated result from the FEM model is consistent with that of the classical Ferris’ model. The error percentages of A-weighted SPL, loudness and sharpness predicted by the FEM-ANN are all less than 5%, which suggests that the FEM-ANN model is accurate and effective for SQ evaluation of a low-frequency sound. The proposed hybrid approach can be used to simulate the acoustic behavior of an auditory system, which helps in revealing the mechanism of human auditory perception.

Effects of floor impact noise on psychophysiological responses

The present study analysed the effects of floor impact noise on humans using both psychological and physiological methods. Floor impact noises caused by a standard impact source (i.e. impact ball) and five real impact sources (e.g., human footsteps and dropped objects) were recorded as sound stimuli. During the laboratory experiments, two factors that impact psychophysiological responses were considered: (1) types of impact sources (standard or real sources) and (2) the levels of floor impact noise ranging from 31.5 to 63 dBA in terms of A-weighted maximum sound pressure level (LAFmax). Twenty-one normal-hearing subjects were then asked to judge the noticeability and annoyance caused by the floor impact noises. Meanwhile, the subjects' physiological responses (heart rate: HR, electrodermal activity: EDA, and respiration rate: RR) were monitored throughout the experiments. Noise annoyance and noticeability increased with increases in noise levels, the impact ball resulted in higher noticeability and annoyance ratings than real sources. All physiological measures varied significantly with noise exposure; HR decreased, whereas EDA and RR increased. The results show that the physiological responses were not affected by the type of noise source. In addition, the noise level was found to be significantly related to EDA and RR changes, whereas the relationship between the noise level and HR was not found to be significant.

Internal noise reduction in railway vehicles by means of rail grinding and rail dampers

Interior noise reduction has become an important concern in railway operating environments due to the influence of increased speeds and reduced vehicle weights on energy efficiency. Two types of measures, rail grinding and rail dampers, were proposed to reduce the internal noise within railway metro vehicles on a particular curve section of a Chinese metro line where the internal noise within metro vehicles is so excessive when the train passes that drivers and passengers complain. The dynamic property and track decay rate of the track system were carried out through mechanical shock method first. Then the measurement of rail vibration performance, external noise and internal noise were conducted when the metro train passed through this track section at the required speed. The rail corrugation with a wavelength of 0.06 m is a major cause of the excessive internal noise. After the application of rail grinding, the overall A-weighted sound pressure levels reduced from 85 to 82 dB due to the removal of the rail corrugation and other short-wave irregularities. Moreover, after the further use of rail dampers, the overall A-weighted sound pressure levels within the carriage further decreased from 82 to 74 dB, resulting from the reduction of the wheel/rail external noise transmitted into the vehicle body through leaks in the vehicle body. Therefore, the noise reduction effect of the two presented measures is significant.

Exposure to excessive sounds and hearing status in academic classical music students.

The aim of this study was to assess hearing of music students in relation to their exposure to excessive sounds. Standard pure-tone audiometry (PTA) was performed in 168 music students, aged 22.5±2.5 years. The control group included 67 subjects, non-music students and non-musicians, aged 22.8±3.3 years. Data on the study subjects' musical experience, instruments in use, time of weekly practice and additional risk factors for noise-induced hearing loss (NIHL) were identified by means of a questionnaire survey. Sound pressure levels produced by various groups of instruments during solo and group playing were also measured and analyzed. The music students' audiometric hearing threshold levels (HTLs) were compared with the theoretical predictions calculated according to the International Organization for Standardization standard ISO 1999:2013. It was estimated that the music students were exposed for 27.1±14.3 h/week to sounds at the A-weighted equivalent-continuous sound pressure level of 89.9±6.0 dB. There were no significant differences in HTLs between the music students and the control group in the frequency range of 4000-8000 Hz. Furthermore, in each group HTLs in the frequency range 1000-8000 Hz did not exceed 20 dB HL in 83% of the examined ears. Nevertheless, high frequency notched audiograms typical of the noise-induced hearing loss were found in 13.4% and 9% of the musicians and non-musicians, respectively. The odds ratio (OR) of notching in the music students increased significantly along with higher sound pressure levels (OR = 1.07, 95% confidence interval (CI): 1.014-1.13, p < 0.05). The students' HTLs were worse (higher) than those of a highly screened non-noise-exposed population. Moreover, their hearing loss was less severe than that expected from sound exposure for frequencies of 3000 Hz and 4000 Hz, and it was more severe in the case of frequency of 6000 Hz. The results confirm the need for further studies and development of a hearing conservation program for music students. Int J Occup Med Environ Health 2017;30(1):55-75.

A cohort study on occupational noise induced hearing loss in workers at an iron and steel plant

Objective: To analyze the incidence rate of occupational noise-induced hearing loss in noise-exposed workers in an iron and steel plant from 2006 to 2015. Methods: Using a cohort study method, workers exposed to occupational noise from Jan 1, 2006 to Dec 12, 2015 were followed up and the pure tone hearing test was conducted. In total, 6 297 subjects completed two or more physical checks and the pure tone hearing test and were included in the analysis. The noise exposure level at the workplace and the equivalent continuous A-weighted sound pressure level for workers was monitored and the cumulative noise exposure dose was evaluated. The subjects were divided into low, middle and high exposure groups according to the noise exposure level, and the equivalent continuous A-weighted sound pressure level for 8 hours for each group was 80.6-85.0, 85.1-90.0 and 90.1-103.4 dB (A), respectively. While the RR and 95% CI were derived from unconditional logistic regression models. In logistic regression analysis, confounding factors such as age, gender, smoking habit, drinking habit, high temperature exposure and chemical hazards exposure level were controlled. Results: During the follow-up period, 392 cases of occupational noise-induced hearing loss were diagnosed among the 6 297 subjects, with an incidence rate of 6.23%; 318 cases of high-frequency hearing loss were diagnosed, with an incidence rate of 5.05%; and 74 cases of occupational noise-induced deafness were diagnosed, with an incidence rate of 1.18% . The incidence rates of hearing loss among the high, medium and low exposure groups were 9.22% (158/1 737), 6.49% (204/3 142) and 2.08% (30/1 442), respectively; the rates of high-frequency hearing loss were 7.41% (127/1 737), 5.25% (165/3 142) and 1.80% (26/1 442), respectively; and the rates of occupational noise-induced deafness were 1.81% (31/1 737), 1.24% (39/3 142) and 0.28% (4/1 442), respectively. For the groups corresponding to cumulative noise exposure doses of ≤84.99, 85.00- 87.99, 88.00- 90.99, 91.00- 93.99, 94.00- 96.99, 97.00- 100.99, 101.00- 102.99 and ≥103.00 dB (A) · year, the incidence rates of hearing loss were 0 (0/185), 1.22% (2/164), 2.52% (17/674), 3.83% (35/913), 5.80% (106/1 827), 6.02% (67/1 113), 9.20% (95/1 003) and 18.04% (70/388), respectively. Compared with the low exposure group, the RR of hearing loss, high-frequency hearing loss and occupational noise-induced deafness for the high exposure group were 4.78 (95% CI: 3.22- 7.11), 4.36 (95% CI: 2.84- 6.69) and 6.63 (95% CI: 2.33- 18.82), respectively; and for the medium exposure group were 3.27 (95% CI: 2.22-4.82), 3.02 (95% CI: 1.99-4.59) and 4.52 (95% CI: 1.61-12.67), respectively. Conclusion: The incidence rate of hearing loss for workers exposed to noise in an iron and steel plant was related to the cumulative noise exposure dose, gender, age, educational level, smoking habits, drinking habits and exposure to high temperature.

Comparison between Subjective Evaluation Results of Frequency Component Varied Rubber Impact Sound and Single Numerical Quantities

Floor impact sound is one of the most annoying noise sources in multi-story residential building. People usually do not wear shoes in a floor-heated house, in such cases children’s running, jumping and adult walking generate low frequency impact sound. In order to simulate and test low frequency impact sound in multi-story residential buildings, heavy/soft impact source (rubber all) was standardized in ISO 10140-3, 5 and ISO 16283-2. However there is no single number quantity (SNQ) to evaluate rubber ball impact sound. For the proposition of SNQ on rubber ball impact sound several subject tests were conducted. The most of subjective test focused on level variation. In this study, frequency component of rubber ball and real impact sound, which were recorded in typical Korean residential building, were varied and presented to the subjects using headphone. Subjective loudness were evaluated and compared with several SNQ such as A-weighted maximum impact sound pressure level (LA,F,Max), arithmetic mean level (LiF,avg,Max) and inverse A-weighted maximum impact sound pressure level (LA,F,Max). It was found that LiF,avg,Max and LA,F,Max show higher relationship than other SNQs.