Enhancing noise reduction in 3D-printed earmuffs through geometric design of internal structures

Exposure to occupational noise remains a significant health hazard, necessitating effective hearing protection strategies. This study evaluated the impact of internal geometric design on the noise attenuation performance of 3D-printed earmuffs fabricated from acrylonitrile butadiene styrene (ABS)/clay nanocomposite. Five earmuff variants were produced with identical external dimensions but differing middle-layer geometries: hexagonal (honeycomb), square, circular, rectangular, and triangular. Insertion loss (IL) was measured across frequencies from 125 Hz to 8000 Hz using an Acoustic Test Fixture (ATF) in accordance with ANSI/ASA S12.42-2010 Methods for the Measurement of Insertion Loss of Hearing Protection Devices in Continuous or Impulsive Noise Using Microphone-in-Real-Ear or Acoustic Test Fixture Procedures and ISO 4869-3:2007 Acoustics-Hearing Protectors-Part 3: Measurement of Insertion Loss of Earmuff Type Protectors Using an Acoustic Test Fixture. Results showed that geometric configuration notably influenced sound attenuation. The triangular structure achieved the highest IL at 500 Hz (25.5 dB) and 8000 Hz (31.8 dB), while the hexagonal design provided superior broadband performance, particularly at 1-4 kHz (19.1-24.9 dB). In contrast, all structured designs exhibited reduced effectiveness at 125-250 Hz, likely due to structural resonance and minor seal leakage. These findings demonstrate that strategic geometric patterning of internal earmuff layers can enhance passive noise control without increasing weight or material cost.