Objective: Psychoacoustics links the physical parameters of sound with the sensation and perception that they evoke. The Intensity, frequency and timing are three basic characteristics of sound that are considered in most psychoacoustic studies. There is no study in Iran regarding just noticeable difference (JNP) of sound intensity, frequency and time. Method: This cross-sectional analytical study was performed on 28 normal right-handed subjects (14 males and 14 females) in the age range of 18 to 30 years. The subjects were randomly selected from among people without any previous ear disease or surgery, neurological disorder, and speech, language and hearing difficulties. The JND of sound intensity relative to the stimulus level, the JND of sound frequency relative to the stimulus frequency, and the shortest sound gap detection relative to the level of stimulus intensity were measured by conducting "intensity discrimination", "frequency discrimination" and "gap detection" tests and analyzed based on ear and sex. Results: The JND of sound intensity and the shortest amount of sound gap detection improved (decreased) at higher stimulus levels in both "intensity discrimination" and "gap detection" tests. The JND of sound frequency increased as a function of frequency increments, and the ear and sex had no effect on results. Conclusion: Our results are concordant with previous studies and can be considered as a basis for proposing related research studies and can also be used in clinical evaluations of auditory disorders.

Background: Polyurethane foam is a sound-absorbing material. The affective factors of its sound absorption have not received much attention in Iran. Therefore, the present study was conducted with aim to investigate the effect of sample thickness, air gap thickness, and sound intensity on sound absorption rate of open cell polyurethane foam.Methods: To conduct this experiment, the impedance tube was built based on the standards and the absorption coefficient of open cell polyurethane foam with thicknesses of 25 and 50 mm was measured. Then, both foam thicknesses were evaluated in six different sound intensities of 70, 80, 90, 100, 110, and 120 dB. Furthermore, the absorption coefficient of the 25 mm thick foam with 5.5 cm of air and the 50 mm thick foam with 3 cm air layer at end of samples were measured. Then, the absorption coefficient of 40 mm thick foam was measured with 1 cm air layer and 2 cm of foam on either side, and then, 1 cm air leyer and 4 cm of foam on either side. Findings: The accuracy and efficiency results showed that the impedance tube can be used with a correlation coefficient of 0.98. The effect of sound intensity on sound absorption was not significant in either of the two thicknesses of polyurethane foam. The air layer at the end of the 25 and 50 mm thick foam increased the absorption in average and high frequency ranges. The absorption coefficient of 40 mm thick foam with 1 cm of air in the middle increased in all frequencies, and of the sample with 1 cm air at the end increased in high frequencies, compared to the 5 cm thick foam without air layer.Conclusion: According to the results of this study, the sound absorption coefficient of the open cell polyurethane foam can be improved with a higher thickness and by inserting a layer of air at the end or in the middle of the absorbent material.

Sound is one of the forms of mechanical energy and the two main characteristics of sound are intensity or power and frequency or wavelength of sound.their performance against the incoming sound wave, industrial silencers can be divided into two general groups of resonating and absorption silencers, the main difference between these silencers is the release of sound energy from the channeling system, which is one of the common examples of the use of resonating type silencers, their use in It is the internal combustion engines that distinguish absorption silencers from the resonator type based on the fact that the main and visible part of the act of muting the sound is achieved by changing sound energy to heat energy.The goal of this article is to design a muffler based on the breaking of sound frequencies resulting from the movement of fluid in the exhaust output of vehicles, which leads to a reduction of at least 50 db of sound and gives the operator enough peace and concentration. In this article, after examining three types of mufflers, absorbent mufflers that use the properties of porous absorbent material to absorb passing sound and are the simplest form of mufflers, have been selected, analyzed and reviewed and are suitable for the OM457 engine of Idem Industrial Company. It designed for maximum inlet exhaust temperature is 520 and for the maximum kW power is 315 with the maximum discharge relative pressure of 185 mbar for homogenization with the standard atmosphere.

Knowing the intensity and duration of rainfall can be useful in many environmental analyses, including the estimation of rain erosivity and soil erosion. There are various devices to record the intensity and duration of rainfall, but purchasing and maintaining them are costly and often requires an operator to take care of them. The present research deals with the feasibility of using the analysis of sound signals caused by the collision of droplets with surfaces and objects in nature to determine the intensity and duration of rainfall. For this purpose, in the laboratory of the Department of Soil Science, Faculty of Agriculture, University of Tabriz, in 2022, rain simulators were designed to produce rains of different intensities, then, the sound signals caused by the impact of raindrops with the metal tray that was placed under the rain were recorded and transferred to the computer for processing. Then, the frequency size of audio files was extracted in MATLAB software. The results showed that with the increase in rainfall intensity, the audio amplitude and frequency size of the audio signals increased. Then, the frequency measurements were automatically placed in two clusters in SPSS software using the two-stage clustering method. Then the mean and standard deviation of each cluster were calculated and according to the correlation of each with each other and with the intensity of rainfall, and in order to avoid the multi-collinearity phenomenon, only the average of the second cluster was used as the input of gene expression programming and linear regression models. In order to test the accuracy and correctness of the results obtained from the models, the coefficient of determination (R2), root mean square error (RMSE), geometric mean of error ratio (GMER), geometric standard deviation of error ratio (GSDER) statistics were used. The values of R2, RMSE (mm/h), GMER(mm/h) and GSDER (mm/h) for the gene expression programming model in the training series data were 0.97, 1.85, 1.11 and 1.09 respectively and for the validation series data were 0.96, 2.05, 1.14 and 1.12 respectively. While the values of the above criteria in the regression model were 0.94, 2.74, 1.25 and 1.34 respectively for the training series data and 0.92, 2.91, 1.28 and 1.37 respectively for the validation series data. The results of the above statistics indicate that the gene expression programming model is relatively more accurate than the regression and overestimation model, and the estimated data of the regression model is relatively more spread than the gene expression programming model.

Exergy analysis is a method that can calculate thermodynamic losses by means of second law of thermodynamic. In this study, exergy analysis has been performed for the silencer of OM314 diesel engine. Irreversibility due to heat transfer from silencer to environment, silencer's internal irreversibility and total irreversibility for different conditions of engine operation have been measured and calculated. For finding out the relation between irreversibility and exit sound intensity, simultaneously, exit sound intensity from the silencer has been measured. Results illustrate that by tripling of silencer irreversibility, exit sound intensity increases only 10 percent. Also the results shows that the irreversibility due to heat transfers have the most contribution in total irreversibility of silencer. So from the view point of second law of thermodynamics, it seems that cooling the silencer can be an effective method for sound reduction. Also results illustrate that, sound intensity of silencer is basically dependent to engine speed.

Introduction: Noise pollution is a significant factor impacting employee health. A large number of employees face noise problems in their work or life. Therefore, this study sought to examine the noise condition in industrial workshops where the worker population of less than 20 individuals. Materials and Methods: This descriptive-cross-sectional research was carried out in 500 small industrial workshops, each with fewer than 20 employees, comprising automotive service workshops, turning operations, plastic industries, door and window manufacturing, woodworking, CNC facilities, metalworking industries, and welding workshops. The chosen workshops were selected from a pool of 1000 available workshops through simple random sampling. Initially, the workshop gathered information regarding the maintenance condition of the devices, the noise type, and the device’s response time. workshop, including the maintenance status of the devices, the type of noise, and the response speed of the device, was recorded. Subsequently, a straightforward TES52A sound level meter was utilized to measure the sound. Results: The sound measurement findings indicated that 63.2 percent of the workshops exhibited a desirable sound level. The minimum, maximum, mean and standard deviation of the sound were 45, 105 and 79 ± 11.3 dB, respectively. 82.8% of the workers in the workshops exposed to sound did not utilize personal protective equipment. The maximum sound intensity was recorded in the occupational categories of door and window manufacturing (90.7 dB) and woodworking (88.7 dB). Additionally, the Spearman correlation coefficient for the equivalent sound level and workshop volume was 0.315 and statistically significant (P<0.001). Conclusion: The findings indicate that the noise level in jobs like door and window manufacturing and woodworking exceeds the allowable limit, and the majority of employees do not utilize hearing protection devices. Additionally, the dimensions of the workshop and the number of individuals working in each workshop were recognized as factors affecting the equivalent sound level.

The accuracy of the large eddy simulation method near the wall depends on the non-dimensional distances y ^ +, x ^ + and z ^ + of the grid in the boundary layer. Study on these non-dimensional distances have been made in various research. But these values ​​can vary depending on the physics of the problem and the phenomena being studied. In this article, the effect of these parameters is investigated on sound estimation. For this purpose two types of grids with different setting have been used. The results obtained from both grids have been validated using experimental data in the one-third octave band . In the study of vortices, using flow lines and Q-criteria, it was observed that the use of larger non-dimensional distances on the wall surface increases the longitudinal scale and strength of vortices and as a result the strength of acoustic waves is estimated to be higher than the actual value. This issue was studied from different directions and it was observed that the differences between the two grids varies at different angles. The maximum difference between the total average sound pressure level obtained by the two meshes is about eleven decibels at an angle of 135 degrees. Considering that the two-dimensional distances used in the both grids were within the suitable ranges suggested in the previous study, it can be said that more stringent requirements for non-dimensional distances are needed to accurately predict the strength of acoustic waves.

In this article, an attempt has been made to estimate the amount of sound transmission loss in a flat oval channel by applying the approach of statistical energy analysis. Correct estimation of sound transmission loss in an air conditioning channel is of great importance due to the harmful effects of noise pollution in the environment on human health. Simulation with the statistical energy analysis method is a powerful approach to estimate sound and vibration in problems in which we deal with complex and multi-part systems; is considered. In this method, first, a system is divided into several subsystems, and then by writing a matrix equation that includes the energy exchanges between subsystems and energy loss coefficients; It is investigated from the perspective of vibration and sound estimation.On average, the model presented in this research is able to estimate the sound transmission loss in different dimensions of the air conditioning channels according to the experimental results in the accuracy range of ± 2.5 dB. Considering that it seems that the results obtained from modeling with this method are in good agreement with the experimental data; The results of this research can be used as an efficient approach to estimate noise in oval shaped channels stretched in different lengths.