Acoustical role of ear canal in exposure to the typical occupational noise levels

Background: Exposure to noise associated with injuries has become a public health issue in recent years. This study aimed to show the role of the acoustical structure of the ear canal on the typical occupational sound pressure levels at different frequencies. Methods: This cross-sectional study was done on 20-30-year-old participants. White noise was used at 3 levels, including 75, 85, and 95 dB as the stimulus sound pressure levels (SSPLs). The speakers had a 1.5-meter distance from the participants and at the height of 87 centimeters from the lab ground and were located in front of the participants. The SSPLs were measured outside (cavum part of the external ear) and inside the right ear of each participant. Measurements were done at the total sound pressure level and in the 1/1 octave frequencies. The duration for each measurement was 10 seconds. The independent sample t test was used for the statistical analysis, and the equality of means were rejected at p<0.05. Results: There were 30 (50%) males out of the 60 participants. The mean ± SD for the age of all the participants was 23.29±2.93 years. The total sound pressure level difference between the inside and outside of the ears of male and female participants was statistically significant (p<0.001) at the stimulus sound pressure levels. The peak resonance was observed in the frequencies 2000 Hz and 8000 Hz for males and 8000 Hz for females. Conclusion: The ear canal can amplify the sounds and increase the sound pressure levels. This amplification was found to be greater for males than for females.