Measurement, modelling and simulation of earphone sound signature

Abstract

Earphones are no longer a novelty or substandard to large sound systems. People use them for music reproduction, on the go and even at home. However, the frequency responses of the earphones nowadays available are as different as the exterior designs of the earpieces. This master thesis aims at identifying the contributing factors, from a psycho-acoustics point of view, to a good sound signature for earphones. It also presents the components necessary to achieve such a sound signature from a design point of view. To do so, this thesis presents an important literature review and highlights an issue not present when sound reproduction is performed with a distant source: the variability of the coupling between the ear and the earphone. In a first part, the psycho-acoustics of listening with earphones is explained because earphones do not provide important cues that listeners would naturally perceive when listening to a distant source. Various perceptual audio descriptors such as loudness, frequency response and other metrics are also presented in order to establish the requirements for earphone design. In a second part, the measurement of earphones and the measurement tools available to these measurement are presented. The concept of electrical impedance, frequency response and distortion measurement are covered. The reliability of these tools as indicators of the variability of the coupling between the ear and the earphone for a given population is compiled from various published studies. In a third part several modelling methods, such as the lumped-elements, control-system block diagrams and two-port networks, are detailed and the models of electro-acoustic transducers and passive components are covered. A simulation is performed on earphones recently developed by the industrial partner of this work with software tools likeMATLAB®, Simulink® and Simscape®. Lastly, this thesis presents areas identified during this research that would benefit from further research, such as the need for a new broad-band measurement apparatus and the need for psycho-acoustic studies on the impact of the coupling between the ear and the earphone. A practical solution to the delicate question of the earphone/ear coupling variability is offered and relies on the automated and individualized adjustment of the earphones frequency response based on the measurement -by the digital audio player- of the electrical impedance of the earphones.

Date	20 Sept 2013
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Jérémie Voix (Supervisor)