Patent ID: 8238567

Claim:
A method comprising: analyzing an inner signal output by an inner microphone disposed within a cavity of a casing of an earpiece of a personal acoustic device and an outer signal output by an outer microphone disposed on the personal acoustic device so as to be acoustically coupled to an environment external to the casing of the earpiece; determining an operating state of the earpiece based on the analyzing of the inner and outer signals; wherein: analyzing the inner and outer signals comprises comparing a signal level of the inner signal within a selected range of frequencies to a signal level of the outer signal within the selected range of frequencies; and determining the operating state of the earpiece comprises determining that the earpiece is in the operating state of being positioned in the vicinity of an ear at least partly in response to detecting that the difference between the signal levels of the inner signal and the outer signal within the selected range of frequencies is within a maximum degree of difference specified by a difference threshold setting; and imposing a transfer function on the outer signal that modifies a sound represented by the outer signal in a manner substantially similar to the manner in which a sound propagating from the environment external to the casing to the cavity is modified at a time when the earpiece is in the operating state of being positioned in the vicinity of an ear.