Prediction of earplug attenuation based on impedance measurements in the ear canal

The level of the attenuation is strongly affected by the amount of leakage. The leakage through an earplug is traditionally divided into three parts; sound propagation between the earplug and the ear canal wall, vibration of the earplug and sound propagation through the material. The last leakage path is usually much less efficient than the two others. Simple models of these leakage paths can be incorporated into an impedance analogy model of the transducers together with a model of the outer and middle ear to predict the attenuation of a badly inserted earplug. The measured impedance contains information about the length and area of the remaining part of the ear canal, the stiffness of the tympanic membrane, the middle ear and the cochlea. Some information about these quantities can be extracted from the impedance measurements.