A 
noise canceling and communication 
system is described. An in-ear device is adapted to fit in the 
ear canal of a device user. A passive 
noise reduction element reduces 
external noise entering the 
ear canal. An external 
microphone senses an external acoustic 
signal outside the 
ear canal to produce a representative external 
microphone signal. An internal 
microphone senses an internal acoustic 
signal proximal to the tympanic membrane to produce a representative internal 
microphone signal. One or more internal sound generators produce a 
noise cancellation signal and an acoustic communication signal, both directed towards the tympanic membrane. A probe tube shapes an 
acoustic response between the internal sound generator and the internal microphone to be relatively constant over a wide 
audio frequency band. An 
electronics module is located externally of the ear canal and in communication with the in-ear device for 
processing the microphone signals using a 
hybrid feed forward and feedback active 
noise reduction algorithm to produce the noise cancellation signal. The 
noise reduction algorithm includes a modeling component based on a 
transfer function associated with the internal sound generator and at least one of the microphones to automatically adjust the noise cancellation signal for fit and geometry of the ear canal of the user. The communication component also includes a modeling component based on a 
transfer function associated with the internal sound generator and at least one of the microphones to automatically adjust the communication signal for fit and geometry of the ear canal of the user and to assure that the communication signal does not interfere with the 
noise reduction algorithm and that the noise cancellation signal does not interfere with passing of the communication signal.