It is difficult to measure or estimate accurately the pressure or the volume velocity at the eardrums of human subjects. A method that enables us to determine both the pressure and the volume velocity evoked by an insert earphone in the ear canal is developed. The method can be used to accurately estimate pressure frequency response at the eardrum. A pair of headphones with in-ear microphones is modeled as a Norton equivalent electroacoustic volume velocity source. A custom-made new miniature particle velocity sensor is used in the modeling of the velocity source. Measurements made with the particle velocity sensor and those made with miniature microphones show that the presented estimation method is accurate up to 12 kHz. The method can be applied to bin aural reproduction as well as to audiological measurements.