The acoustic transfer functions of external ears with or without headphones affect the features of perceived sounds and vary considerably with listeners and headphones. A method for estimating the frequency responses of external-ear transfer functions from the sound at the entrance of a blocked ear canal (or from the input of a headphone) to the sound at the eardrum for different listeners and headphones is developed based on an acoustic signal model of external ears. The model allows for

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... ng realistic data about individual external ears and headphones and is advantageous over current standard ear simulators with fixed structures limited to simulating average ear canals and eardrum impedances below 10 kHz. Given different eardrum impedances, ear canal shapes, lengths, and headphones, the frequency responses of external-ear transfer functions are estimated and presented. In addition, a method of determining the Norton equivalent volume velocity or Thevenien equivalent sound pressure sources of a headphone from sound pressure signals in an acoustic tube is presented. These methods are validated via direct measurements and expected to have applications in headphone sound reproduction, headphone and hearing aid design, and audiometric and psychoacoustic measurements to produce desired sounds at the eardrums of different listeners.