Journal of Health and Safety at Work

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Introduction: The acoustic performance of natural fiber adsorbents has been investigated in numerous studies. A part of these materials show a poor adsorption within the frequency range of less than 1000 Hz. In the present study, attempts were made to investigate the effect of layout sequence of double-layered composites consisting of natural and synthetic fibers on improving the acoustic adsorption coefficient of natural fiber in the low-frequency range (63 to 1000 Hz) using the numerical finite element method.
Material and Methods: In this study, the finite element method and the Johnson-Champoux-Allard model in COMSOL software version 5.3a were used to investigate the acoustic performance of the double-layered composites consisting of natural and synthetic adsorbents. The acoustic absorbers under study included date palm fiber, polyurethane foam and cellular rubber. Each double-layered composite included a date palm fiber with 10mm in thickness and a synthetic adsorbent (polyurethane foam or cellular rubber) with 10mm in thickness. In sum, four double-layered composite structures with different layouts of adsorbents in each structure were studied.
Results: The location of natural fiber can play a critical role in the acoustic performance of the double-layered composite structures such that comparing the studied double-layered composites revealed that when the natural fiber was the first layer exposed to the normal sound in the double-layered composites with 20mm in thickness, the trend of acoustic performance was approximately the same as the single-layered composite of natural fiber with 20mm in thickness; but in the composite structures, when the synthetic adsorbent was the first layer exposed to the sound, the trend of acoustic absorption was improved.
Conclusion: On the basis of the results, the double-layered composite structure with a higher-density and lower-porosity upper layer showed a better acoustic absorption trend than the single-layered composite including the natural adsorbent.

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Introduction: Exposure to noise is one of the most common harmful factors in the dental profession that can have significant consequences. Unfavorable acoustic conditions of the environment can also worsen the conditions and lead to reduced speech clarity, auditory fatigue, and reduced quality of communication between the doctor and the patient. In this regard, designing effective acoustic interventions can play an important role in improving sound.
Material and Methods: This study was conducted in an academic dental clinic. After measuring the sound pressure level, reverberation time, and speech transmission index, the amount of rock wool absorber required was determined using the Sabin formula. The panels were structurally installed on the clinic walls, and after 24 hours, the sound pressure level, RT60, and STI were measured again, and appropriate statistical tests were used to determine the effect of the intervention.
Results: The results showed that the sound pressure level before and after the panel installation was significantly different and decreased after the intervention (p-value <0.05). The reverberation time at the dominant frequency of 2000 was 0.992 seconds before the intervention and reached 0.599 seconds after the intervention (p=0.027, z= 2.207). The speech transmission index in the center of the room improved from 0.64 and the “average” level to 0.85 and the “excellent” level, indicating an increase in speech clarity.
Conclusion: The acoustic intervention was able to bring the clinic’s acoustic indices closer to the recommended ranges. The significant reduction in reverberation time and sound pressure level along with the increase in the speech clarity index indicates the high efficiency of this intervention. Utilizing sound absorbers can be a low-cost and feasible solution to improve acoustic conditions and improve speech communication in dental treatment and educational environments.