Simulating external-ear transfer functions

It is known that current standard ear simulators as used in standard dummy heads (or used separately) can only simulate acoustical responses of typical human ears below 10 kHz due to difficulties in constructing accurate acoustic simulators of eardrum impedance at higher frequencies. Those ear simulators are not satisfactory when it is desired to simulate realistic sound pressure responses over the full range of audible frequencies at the eardrums of average ears, or those of non-typical ears. Considering that digital acoustic signals have been widely used in the analysis of acoustic systems, without constructing various acoustic ear simulators, this paper presents a new method of constructing an analytical digital filter to simulate the acoustic transfer function of external ears given the radiation impedance of the pinna, the eardrum impedance and the ear canal cross-sectional area function. The filter is needed to synthesize the sound pressure response at the eardrum of a listener given the sound pressure signal obtained at the entrance to the ear canal. It is also needed to simulate the transfer functions of external ears wearing a device (such as an earphone, insert, headphone or hearing aids) to help understand the combined effect of the device and the ear canal and improve the design of the audio systems. The accuracy of the simulation is evaluated by comparing it with the transfer function measured on a standard ear simulator, and it is found that they agree with each other very well.