Showing 37 results for Noise
Roohalah Hajizadeh, Ali Khavanin, Ahmad Jonidi Jafari, Mohammad Barmar, Somayeh Farhang Dehghan,
Volume 9, Issue 4 (12-2019)
Abstract
Introduction: Nowadays multiple techniques have been developed to noise control. One the most important way is the control based on sound absorption and insulation. The purpose of current study was to improve the acoustic properties of soft polyurethane foam regarding combined sound absorption and insulation characteristics.
Materials and Methods: Polyacrylonitrile and polyvinylidine fluoride nanofibers are fabricated using solution electrospinning technique. Nano-clay particles (montmorillonite, 1-2 nm in diameter) were purchased from Sigma-Aldrich, Inc. Experimental design was prepared using Design-Expert ver.7 software. The 50 samples of nanocomposites were fabricated on the basis of experimental run. The measurement of sound transmission loss and the absorption coefficient was conducted using BSWA SW477 550005 Impedance Tubes according to the standard ASTM E2611-09 and ISO10534-2, techniques. Response surface methodology (RSM) with central composite design (CCD) was applied to optimize the conditions to produce nanocomposites for each frequency range.
Results: The polymer nanocomposites had the higher combined sound transmission loss and the absorption coefficient than pure polyurethane foam. Their combined transmission loss and the absorption coefficient in the low, middle and high frequency range was 02.02, 1.91 and 2.53 times higher than the pure polymer. The combined transmission loss and the absorption coefficient in all frequency ranges have been increased by increasing the thickness of the composites and air gap. At a thickness of 2 cm, the combined composites, sound transmission loss and the absorption coefficient increased with the increase of content of both nanofibers. The highest combined transmission loss and the absorption coefficient was observed when mass fraction of nanofibers was in at its maximum level.
Conclusion: This study showed that the adding nano-clay particles, polyacrylonitrile and polyvinylidine fluoride nanofibers to polyurethane foam can lead to increased sound transmission loss and the absorption coefficient. The obtained optimized nanocomposite can be applied to noise control where requiring the absorption as well as reduction of sound transmission.
Milad Abbasi, Siavash Etemadinezhad, Ahmad Mehri, Maryam Ghaljahi, Rohollah Fallah Madvari, Roghayeh Jaffari Talaar Poshti,
Volume 10, Issue 2 (5-2020)
Abstract
Introduction: Although noise characteristics such as intensity and frequency are the main cause of detrimental effects, it is important to pay attention to the personality traits of individuals as the host of adverse health effects. The aim of this study was to investigate the effect of personality traits on sensitivity, annoyance and loudness perception due to exposure to high frequency sound.
Material and method: This interventional and experimental study was carried out among 80 undergraduate and postgraduate students in 2017. First, examinee were exposed to a high frequency noise at 65 dBA for one hour in an acoustic room. Then, to determine amount of annoyance, sensitivity, loudness perception and to investigate personality traits, questionnaire of noise annoyance, noise sensitivity, loudness perception and Eysenck personality inventory was used, respectively. Finally, Chi-square, independent t-test and multivariate analysis of variance (MANOVA) were used to data analyze.
Results: The mean±SD of sensitivity, annoyance and loudness perception were 54.08±7.71, 7.0±1.53, and 2.79±1.13, respectively in this study. The mean scores of sensitivity, annoyance and loudness perception were significantly different in terms of personality traits, so that their average was higher in the neurotic and introverted. Based on MANOVA test results, personality traits had a significant effect on sensitivity, annoyance and loudness perception of individuals. In a way, the neuroticism and introversion had the greatest effect on the sensitivity and annoyance, respectively.
Conclusion: The results of this study showed that personality traits such as introversion and neuroticism can affect the sensitivity, annoyance and loudness perception of individuals.
Haniyeh Ekhlas, Hamidreza Pouragha, Mohammadreza Monazzam, Ramin Mehrdad, Parisa Bahrami, Mojgan Zaeimdar,
Volume 11, Issue 4 (12-2021)
Abstract
Introduction: Previous studies have been conducted on the effects of exposure of industrial workers to high levels of noise and their association with mental health or exposure of people to harmful levels of environmental noise. In this study, we investigated the association between moderate noise levels and the symptoms of depression, anxiety, and stress in non-industrial workers.
Material and Methods: This study is a Cross-Sectional study that was conducted using the enrollment phase data of the Tehran University of Medical Sciences Cohort (TEC) study. The study population consisted of 3899 workers of Tehran University of Medical Sciences who were employed in seven occupational groups of the university, Office Workers, Healthcare workers, technical personnel, services workers, security guards, and radiology-radiation units. Exposure to moderate noise level was examined using the Leq10min index, and the Depression Anxiety Stress Scales were examined on the mentioned population by DASS-42 questionnaires.
Results: The results showed that the prevalence of severe to very severe symptoms of depression, anxiety and stress were 8.2, 7.9, and 11% respectively. Also, it was observed that 14.5% of the participants of the study were exposed to noises of more than 70 dB(A). Furthermore, the results indicated that the highest average noise was equal to 71.3 dB(A) for the technical staff group, and the lowest value with an average of 59.1 dB(A) was recorded for the office workers group. The symptoms of severe to very severe depression was associated with exposure to noises above 70 dB(A) (OR:5.22) anxiety (OR:1.16), stress (OR:1.17) and socioeconomic status (OR:1.84). The severe to very severe anxiety was associated with stress (OR: 1.25). On the other hand, the symptoms of severe to very severe stress was associated with variables of age (OR:0.99), gender (OR:0.46), socioeconomic status (OR:1.52), having job management position (OR:0.81) and having healthcare working job (OR:0.65).
Conclusion: Regarding the obtained results of the present study, it was concluded that exposure to moderate noise levels had positive and significant association with depression in non-industrial workers. In non-industrial work environments, exposure to moderate noise levels is and can be independently associated with depression.
Monireh Khadem, Elham Kazemi Rad, Mohammad Reza Monazzam Esmaeilpoor, Maryam Mirzaei Hotkani, Sajjad Mozaffari, Amir Abbasi Garmaroudi,
Volume 12, Issue 1 (3-2022)
Abstract
Introduction: One of the most important complications of exposure to noises is changes in the gene expression patterns. Irreversible damage to the inner ear, such as noise-induced hearing loss (NIHL), is caused by tissue damage and changes in the gene expressions in the auditory system. Changes in the GJB2 gene expression pattern lead to autosomal deafness at different loci. The present study aims to evaluate the GJB2 gene expression in cochlear tissue exposed to white noise.
Material and Methods: In this study, ten male Westar rats were divided into two experimental (W1, W2) groups of six rats and a control (normal) group of four rats. Two experimental groups were exposed to constant white noise in the frequency range of 100-20000 Hz and the sound pressure level of 118-120 dB. In order to study the histology and gene expression, after a cochlea biopsy, the histological tests, RNA extraction, cDNA synthesis, and qRT-PCR analysis were performed.
Results: The results showed that the transcript level of GJB2 was significantly decreased in both experimental groups W1 and W2 by 0.02 and 0.12-fold, respectively (p <0.05). Also, the results of the histological study showed that cochlear tissue was more seriously damaged in the W1 group than W2.
Conclusion: It can be concluded that a significant reduction in the GJB2 gene expression and irrevocable damage to auditory nerve ganglion and Reissner membrane (vestibular membrane) caused changes in the gene expression patterns in cochlear tissue and developed the risk of non-syndromic sensorineural hearing.
Azar Mehrabi Matin, Mahsa Alefi, Mohammad Reza Monazzam, Adel Mazloumi, Kamal Azam,
Volume 12, Issue 1 (3-2022)
Abstract
Introduction: The noise could affect some aspects of human health, including the cognitive performance. In addition to sound pressure level and exposure time, the psychoacoustic features of noise may cause destructive effects on humans. A few recent studies have been conducted on effect of sound quality on cognitive performance. This study aims to find the noise loudness and sharpness levels as the most destructive effects on human cognitive performance.
Material and Methods: This was a cross-sectional study on 10 male students of Tehran University of Medical Sciences. The Noises were generated in two channels that the left channel produced the pink noise as a background noise. The pink noise loudness and sharpness were 19.7 sone and 2.49 acum, respectively. The right channel generated noises with different loudness and sharpness levels the noise loudness ranged from 8.87 to 67.9 sone and the noise sharpness ranged from 1.07 to 6.4 acum. Finally, ten noises with different loudness and sharpness were applied. The students were exposed to ten different types of noise and a silent condition. The Mathematical Problem Solving Task (MPST) test was performed to assess cognitive performance. The reaction time and the accuracy rate were measured after 5 minutes of noise exposure. Data were analyzed by SPSS (ver. 22). P< 0.05 was considered as significant level.
Results: The mean reaction time and the mean accuracy rate increased with the sharpness level. However, alteration in the loudness and sharpness levels had no significant effect on the speed and accuracy of students. Performance speed increased in noise 3 with the highest loudness (L=67.9, SH=1.07) in comparison with the silent condition (p-value=0.05). The mean accuracy rate in exposure to the noise 9 reduced in comparison with silence (p-value=0.04)
Conclusion: Different levels of psychoacoustic features had no significant effect on the cognitive performance parameters. Although, the accuracy rate and the reaction time decreased in noises 9, the sharpest noise, and 3, the loudest noise, in comparison to the silence, respectively.
Esmaeil Karami, Mohammadreza Monazzam, Keykaous Azrah, Mehdi Mohammadian, Zahra Goodarzi,
Volume 12, Issue 1 (3-2022)
Abstract
Introduction: Over recent years, various programs have been conducted to reduce noise, indicating the increasing concerns of society over noise pollution. This study has been performed to enhance the performance of parallel barriers on two sides of a highway considering the surrounding buildings.
Material and Methods: The 2D boundary element simulation method was employed to predict the noise reduction in barriers. Regarding the effect of buildings and water canals, various kinds of models were investigated to compare the effectiveness of different boundary barriers in real conditions from a listener’s perspective.
Results: The use of a single YA model could improve the performance of parallel barriers by 3.5 dB compared to that of a TS model. Moreover, by using a pair of barriers, no significant change was observed in the performance of the second barrier. However, by using parallel barriers along the surrounding buildings, the TD model improved the efficiency by 3 dB compared to the TS model. The rise in the frequency resulted in remarkable adverse effects on the barrier performance, such that the surrounding buildings at a distance of 8 m had a negative effect on the performance of the parallel barriers by almost 8.34 dB.
Conclusion: In general, by ignoring the buildings, the use of a pair of TZ barriers showed a higher performance. Meanwhile, by considering the buildings in the design model, the TD model was found to be optimum. Therefore, it can be concluded that choosing an ideal barrier only based on the noise behind it cannot indicate its behavioral and acoustic characteristics in a real environment.
Shoaib Ghasemi, Fatemeh Fasih-Ramandi, Mohammad Reza Monazzam-Esmaeelpour, Soheila Khodakarim Ardakani,
Volume 12, Issue 3 (9-2022)
Abstract
Introduction: The study of noise has always been of interest to occupational health professionals as a harmful physical factor in the workplace. However, the psychological and psychoacoustic aspects of noise in the workplace have been less studied. This study has dealt with different colors of noise and their applications in psychoacoustics.
Material and Methods: This review study was conducted by searching the databases of Google Scholar, ProQuest, Science Direct, PubMed, and Scopus to extract the articles related to the research subject within a 50-year interval from 1970 to 2020.
Results: Based on the results of the present study, colored noises and white noise seem to have the potential to be used as acoustic stimuli to improve the sleep of employees, especially shift workers, to improve memory and attention, especially in jobs that require high care and attention. Colored noise and white noise have potential applications to improve cognitive function in different occupations to reduce the activity of the sympathetic nervous system and anxiety and stress, especially in jobs with high job stress. Also, these noises are helpful for people’s privacy, especially in the open workplace, for noise masking and noise control purposes, as well as for medicine and treatment of disorders such as tinnitus, ADHD, and hyperacusis.
Conclusion: Paying attention to the colors of noise and their psychoacoustic impacts shows us that the noise impacts are not limited to their undesirable and damaging effects. Instead, their positive and applied aspects should also note. Familiarity with such aspects and their introduction can identify the existing information gaps in this field and pave the way to fill them.
Hamzeh Mohammadi, Somayeh Farhang Dehghan, Soheila Khodakarim Ardakani, Farideh Golbabaei,
Volume 12, Issue 3 (9-2022)
Abstract
Introduction: Studies show that in many cases, environmental hazardous agents such as heat, noise, as well as chemical pollutants cause adverse health effects through the mechanism of oxidative stress. This study has examined the effect of exposure to noise and whole-body vibration (WBV) on some parameters of oxidative stress (enzyme superoxide dismutase (SOD), total antioxidant capacity (TAC), and malondialdehyde (MDA)) of workers in a foundry industry.
Material and Methods: The workers were selected based on the calculations related to the sample size and taking into account the inclusion criteria as well as completing the informed consent form. The level of exposure to noise and WBV was measured according to ISO 9612 and ISO 2631, respectively. For each worker, the time-weighted average was calculated. The level of exposure of workers to the studied stressors was divided into three categories: low, medium, and high. The blood samples were taken from all participants between 7-9 am. Then, via ELISA method according to the protocol of the kit manufacturer, the samples were prepared and analyzed. Univariate analysis of variance was performed to determine the “effect size” of each physical stressors on the studied parameters.
Results: The mean levels of MDA, SOD, and TAC among participants were 22.48 (11.19) nmol / ml, 61.28 (10.97) U / ml, and 1.64 (0.90) mM, respectively. Among the exposure variables, noise had the largest effect on MDA level (B = 0.090), which was not statistically significant (P = 0.865). WBV had the largest effect on SOD level (B = -1.469) which was statistically significant (P = 0.016). None of the studied variables had a significant effect on the TAC level; however, among the exposure variables, the greatest effect was related to WBV (B = -0.077; P = 0.133).
Conclusion: The effect of noise on oxidative stress parameters was not statistically significant. The effect of whole-body vibration on oxidative stress parameters except SOD was not statistically significant. Noise and WBV had increasing effect on MDA and decreasing one on SOD and TAC levels.
Vida Rezaei-Hachesu, Hassan Haddadzade Niri, Saeid Farahani, Mohammad Reza Monazzam Esmaeelpour,
Volume 13, Issue 2 (6-2023)
Abstract
Introduction: Colored noises with acoustic and psychoacoustic characteristics have several biological effects on human or animal health. While studies on auditory effects focus on noise’s physical aspects, its psychoacoustic aspects can also result in health and safety risks. Therefore, this study aims to investigate frequency-based damages due to exposure to colored noise in an animal model.
Material and Methods: Twenty-four male Wistar rats were randomly divided into four groups (6 in each group). The groups included the control (no exposure) and three exposure groups (white, pink, and violet). The rats were exposed to 110 dB SPL for 4 hr/day for 14 consecutive days. Auditory brainstem responses (ABR) with click and tone-burst stimuli were recorded one day before (baseline), 7, and 14 days after exposure. Statistical analyses were conducted using ANOVA and repeated measures ANOVA.
Results: There was a statistically significant increase in ABR threshold values in exposure groups (p<0.05). Hearing threshold shifts in the white noise group showed a homogeneous pattern, violet noise showed an increasing pattern, and pink noise showed a decreasing pattern in low frequencies and a homogeneous pattern with increasing frequency. The highest shift in hearing threshold was observed in exposure groups from day 0 to 14. Additionally, the shift in hearing threshold in the second week was less than in the first one.
Conclusion: The current study observed that noise’s power spectral density affected hair cells’ damage severity. Accordingly, pink noise causes less damage to the cochlea compared to white and violet. Over time after noise exposure, cochlear pathogenesis gradually decreases and hair cell lesions become stable.
Akbar Ahmadi Asour, Mohammadreza Monazzam, Ebrahim Taban, Zahra Hashemi, Somayeh Amininasab,
Volume 13, Issue 3 (9-2023)
Abstract
Introduction: The aim of this study was to investigate the effect of particle size (mesh) on the sound absorption coefficient of the absorbers made from Arundo Donax reed and to determine the optimal mesh for sound absorption.
Material and Methods: After crushing the reed stems in 10, 30, 20, 16, and 40 mesh sizes, they were washed with 5% NaOH. To make the samples 3 and 10 cm in diameter, 10% PVA was used as a binder, and the impedance of the two-channel tube was used according to ISO 10534-2 standard to determine the absorption coefficient. 22 samples of meshes 16 and 20 were made to achieve the optimal mesh based on the optimized RSM method, and the SAA index was used to compare the samples and determine the optimal mesh.
Results: The highest absorption peak was related to meshes 16 and 20 at the frequency of 2500 Hz, which is 0.94 and 0.98 ,respectively. The effect of increasing the thickness and density on the absorption coefficient is evident. The results have shown the effect of increasing the thickness and density on the absorption coefficient in mesh 20 in such a way that by increasing the density from 150 to 250 and the thickness from 10 to 30 mm, the absorption coefficient has increased from 35 to 63.5%. The optimal sample was mesh 20 with a thickness of 30 and a density of 250 kg/m3, which had the highest average absorption (SAA=0.57). The greater distance between the real and imaginary parts of the impedance shows the reactivity of the sample. In mesh 16 this distance is greater, as a result, mesh 16 has more reactivity and correspondingly less absorption.
Conclusion: The role of particle mesh as one of the important and influencing parameters on absorption coefficient has been investigated in this study.
Farough Mohammadian, Mohsen Fallahati, Milad Abbasi, Mojtaba Zokaei,
Volume 13, Issue 3 (9-2023)
Abstract
Introduction: Many industries have multiple factors harmful to health, leading to simultaneous exposure of these factors to each other. Noise is one of the most common physical parameters in the work environment. On the other hand, heat is also increasing due to various energy processes in industries. Therefore, this study was conducted with the aim of determining changes in physiological parameters and visual-auditory attention in acute exposure to heat and noise.
Material and Methods: In this experimental study, 72 individuals (36 men and 36 women) aged between 23 and 33 years participated according to the inclusion criteria. In total, 12 different test modes were performed (3 temperature levels and 4 noise pressure levels). The test was conducted for each person in 4 steps during a specific day. The duration of exposure to each condition was half an hour, and a half-hour rest was given between each test condition. Saliva samples of each subject were collected before and immediately after exposure to noise and heat. Also, The Integrated Visual and Auditory (IVA) was recorded by the participants simultaneously.
Results: The results of combined exposure to noise and heat on visual and auditory attention showed that only two modes of combined exposure, SPL95+WBGT34 and SPL95+WBGT29, caused a significant increase (P < 0.05) in mental workload and a significant decrease (P < 0.05) in visual and auditory attention. In addition, the results showed that independent exposure to noise at the levels of 85 and 95 dB and exposure to heat at higher temperature levels of 34 and 29 degrees Celsius cause a significant increase (P < 0.05) in salivary cortisol after exposure. The results of the effect of combined exposure to noise and heat on salivary cortisol showed that three experimental modes of combined exposure (SPL85+WBGT34, SPL95+WBGT29, and SPL95+WBGT34) caused a noticeable and significant (P<0.001) increase in salivary cortisol.
Conclusion: Indeed, salivary cortisol can be recommended as a physiological index to evaluate noise and heat exposure. It’s also noteworthy that salivary cortisol is more affected by noise and heat exposure than cognitive performance.
Iraj Alimohammadi, Athena Rafieepour, Leila Hosseini Shafiei, Mohammadreza Vafa, Nargess Moghadasi, Shahram Vosoughi, Jamileh Abolghasemi, Rana Ghasemi,
Volume 14, Issue 2 (6-2024)
Abstract
Introduction: Obesity and overweight are major global health challenges. One of the bad effects of noise that has been recently expressed is the effect of noise on obesity. This study aimed to investigate the effect of high-frequency noise exposure on obesity, food intake, and abdominal visceral fat in adult male guinea pigs.
Material and Methods: The animals in this study were 24 adult male guinea pigs randomly divided into 3 groups (control and two case groups). Each case group was separately exposed to high- frequency white noise with sound pressure levels in 65 dB and 85 dB for 5 days per week in 30 days. The food intake was measured daily. The weight of animals was measured at the start and on days 6, 12, 18, 24, and at the end of exposure period. The abdominal visceral fat was extracted and weighted at the end of the study period. The data were assessed using SPSS V.22 software.
Results: ANOVA analysis showed that exposure to high-frequency noise at 65dB and 85dB had a significant effect on weight gain, food intake, and abdominal visceral fat weight (P-value< 0.05) which in the group exposed to the noise with 65 dB was more than other groups.
Conclusion: Based on this study, exposure to high-frequency noise may be an effective factor in obesity and increasing abdominal visceral fat. Further studies are needed to investigate the mechanism affecting weight status following noise exposure.
Sajad Zare, Reza Esmaeili, Fardin Zandsalimi,
Volume 14, Issue 3 (10-2024)
Abstract
Introduction: Cognitive functions play a vital role in how tasks are performed; for this, temporary cognitive and mental dysfunctions could lead to grave consequences, especially when an accurate and prompt response is required. Attention and reaction time to noise are among the most effective exogenous factors on the brain processing mechanism. This study aimed to measure the sustained attention of workers in the steel industry exposed to different sound pressure levels.
Material and Methods: The study was conducted in 4 general stages, including 1- Selecting predictive orientation variables (age, work history, different sound pressure levels); 2- Conducting the Cognitive Performance Test (CPT); 3 Conducting N-BACK Cognitive Performance Test and 4- Modeling cognitive performance changes using model precision methods.
Results: Continuous Performance Test (CPT) results indicated that all three groups’ omission error, commission error, and response time were affected by shift time. All three components increased significantly as the shift ended, decreasing individuals’ cognitive function. Also, the higher noise impact in modeling CPT and N-Back tests indicated reduced workers’ concentration.
Conclusion: These study findings suggested that greater noise weight obtained in test modeling in three-time intervals, i.e., in the beginning, middle, and end of the shift, affected the continuous performance components of the CPT and working memory performance of the N-back test, including workers’ response time and reaction time, with workers’ rate of error increasing and their focus decreasing during the shift.
Mojtaba Zokaei, Milad Abbasi, Mohsen Vahidnia, Mohamad Zarie, Fardin Zndsalimi, Mohsen Falahati,
Volume 14, Issue 3 (10-2024)
Abstract
Introduction: Nowadays, the statistics prove that the underground construction projects in the country are increasing, as well as the number of accidents arising from the unsafe condition of these projects. The purpose of this study was to create a framework of safety and health risk management in the construction phase of the Tehran Metro Line 7 tunnel, using IoT technology.
Material and Methods: In the first stage, the national safety and health standards, laws and requirements related to the mentioned hazards were collected. In the second stage, the criteria and permissible limits of exposure to occupational hazards were determined. Next, sensors with optical, auditory, gas detection, and visual capabilities connected to the network were examined, and computer programming and comparing sensor information with the specified standards were carried out. Finally, intelligent warning and control systems related to the determined hazards were proposed.
Results: In this study, a combined model of risk management utilizing IoT for controlling and monitoring safety and health hazards such as sound, light, explosive and toxic gases was proposed. According to the model, sensors for detecting the mentioned hazards were determined and coded based on the permissible limit of each of the harmful factors.
Conclusion: This study has shown that by employing specialized IT and safety knowledge and utilizing relevant software and hardware, the concept of the Internet of Things can be utilized in precise monitoring of the concentration levels of flammable and toxic gases, as well as monitoring of physical agents such as noise and light in various workplace, such as metro tunnel construction sites.
Zahra Hashemi, Mohammad Javad Sheikhmozafari, Azma Putra, Marzie Sadeghian, Nasrin Asadi, Saeid Ahmadi, Masoumeh Alidostie,
Volume 14, Issue 3 (10-2024)
Abstract
Introduction: Microperforated panels (MPPs), often considered as potential replacements for fiber absorbers, have a significant limitation in their absorption bandwidth, particularly around the natural frequency. This study aims to address this challenge by focusing on the optimization and modeling of sound absorption in a manufactured MPP.
Material and Methods: The study employed Response Surface Methodology (RSM) with a Central Composite Design (CCD) approach using Design Expert software to determine the average normal absorption coefficient within the frequency range of 125 to 2500 Hz. Numerical simulations using the Finite Element Method (FEM) were conducted to validate the RSM findings. An MPP absorber was then designed, manufactured, and evaluated for its normal absorption coefficient using an impedance tube. Additionally, a theoretical Equivalent Circuit Model (ECM) was utilized to predict the normal absorption coefficient for the manufactured MPP.
Results: The optimization process revealed that setting the hole diameter to 0.3 mm, the percentage of perforation to 2.5%, and the air cavity depth behind the panel to 25 mm resulted in maximum absorption within the specified frequency range. Under these optimized conditions, the average absorption coefficient closely aligned with the predictions generated by RSM across numerical, theoretical, and laboratory assessments, demonstrating a 13.8% improvement compared to non-optimized MPPs.
Conclusion: This study demonstrates the effectiveness of using RSM to optimize the parameters affecting MPP performance. The substantial correlation between the FEM numerical model, ECM theory model, and impedance tube results positions these models as both cost-effective and reliable alternatives to conventional laboratory methods. The consistency of these models with the experimental outcomes validates their potential for practical applications.
Seyyed Mohammad Javad Golhosseini, Mohsen Aliabadi, Rostam Golmohammadi, Maryam Farhadian, Mehdi Akbari,
Volume 14, Issue 4 (12-2024)
Abstract
Introduction: Despite the numerous studies on occupational noise-induced hearing loss, there is limited documentation on the vibration effects on the workers’ auditory system. Heavy equipment drivers are exposed to high levels of whole-body vibration (WBV) and noise. Therefore, this study aims to investigate the heavy equipment drivers’ auditory response to WBV exposure and combined exposure to noise and WBV.
Material and Methods: 30 male heavy equipment drivers with an average age of 32.40 ± 4.91 years participated in this study, which was designed based on the repeated measurements model. During 3 defined scenarios of exposure to WBV, combined exposure to noise and WBV, as well as the scenario without exposure, the drivers’ auditory response was measured using distortion product otoacoustic emissions (DPOAE). Statistical analyses were performed by IBM SPSS-25 software.
Results: The range of heavy equipment in-cabin noise was 84-89 dB. Also, the most exposure of drivers to WBV was obtained in the Z axis with an average acceleration of 1.29 m/s2. The DPOAE amplitude of the drivers in all three investigated scenarios showed significant changes (P<0.05); But in comparison between different scenarios, exposure to WBV and combined exposure to noise and WBV had a significant effect on the response of the auditory system of the participants in the study compared to the scenario without exposure (P<0.05). Also, there was a significant difference in the changes of the DPOAE amplitude in different frequencies; Thus, the most changes in the DPOAE amplitude were observed in the frequencies of around 4000 Hz.
Conclusion: The results of this study showed the damaging consequences of exposure to noise and WBV on the auditory response; In addition, the present study provided evidence of synergistic effects of combined exposure to noise and WBV on heavy equipment drivers.
Iraj Alimohammadi, Mahdi Farrokhi, Sevda Javadi, Mozhgan Nouraei, Leila Hosseini Shafeie,
Volume 15, Issue 1 (3-2025)
Abstract
Introduction: A significant contributor to noise pollution in urban areas is automobile exhaust systems, wherein mufflers, as passive devices, are designed to mitigate the noise produced. The dimensions, shape, and configuration of the muffler, along with its associated components and pipes, influence its effectiveness in sound transmission loss. This study investigates the impact of varying the length of the muffler’s connecting pipes and their associated holes on sound transmission loss in reactive mufflers, utilizing software simulation for analysis.
Material and Methods: The research utilized COMSOL 5.5 to simulate the effects of different geometric factors on sound transmission loss in mufflers. Modifying factors such as the length of connecting pipes and the existence of holes led to the development of various designs. Analysis of the results was conducted to assess the impact of each parameter on sound attenuation, enabling a straightforward comparison of acoustic efficiency.
Results: Studies demonstrate that changing the form of pipes at different frequencies produces diverse outcomes. Introducing a perforation prior to the tube and utilizing elongated connecting tubes with expansion chambers can enhance transmission attenuation. On the other hand, transmission loss decreases with longer pipes that lack holes. Lower pitches experience minimal attenuation, whereas higher pitches undergo more loss. Reactive mufflers work best at certain frequencies, where the length of the connecting pipe affects both the acoustic mass and the effectiveness of the muffler.
Conclusion: The results obtained from this study can inform the optimal design of mufflers aimed at enhancing their efficacy in sound transmission loss. Furthermore, it is essential to consider the synergistic impact of the geometrical configurations of the internal pipes within the muffler to minimize sound emissions from the exhaust outlet.
