On the level-dependent attenuation of a perforated device.
To investigate the physical principle governing the level-dependent attenuation of a perforated earplug, a mathematical model is first established with the transfer-matrix method to calculate the noise reduction through a simplified device, one perforated panel with back cavity, mounted in an impedance tube. The model prediction is compared with the measured noise reduction through two series of large-scale devices and one device with the dimensions of the ear canal under continuous noise and sinusoidal excitations. The model helps to improve significantly the level-dependent attenuation of the large-scale device. It also illustrates that the attenuation is not solely determined by the resistance of the orifice, which has been a well accepted design concept, but resulted from an incorporated effect of the acoustic filter comprised of the acoustic impedance of the orifice and other elements in the earplug-ear-canal system. This mechanism can interpret a resonance at low incident levels on improper design and reveal approaches to eliminate it. Finally, the model's potential contributions to the design of a perforated earplug are discussed, along with the threshold of level-dependent attenuation supported with experimental evidence.
Institute of Acoustics, Chinese Academy of Sciences, Beijing 100190-2712, China. lan.chen.ls@gmail.com
Lan
L
Chen
Jinqiu
J
Sang
Xiaodong
X
Li
D000465:Algorithms; D004424:Ear Canal / Q000033:anatomy & histology; D004430:Ear Protective Devices; D004867:Equipment Design; D006801:Humans; D008962:Models, Theoretical; D017711:Nonlinear Dynamics; D011312:Pressure; D013016:Sound