A Study on the Effect of Ventilation Materials on Sound Quality of In-ear Earphones

In this era of true wireless stereo, in-ear earphones have become widely used. Critical factors for determining the frequency response of earphones not only include the microspeaker and the design of the chamber, but also the ventilation material that is attached to the front and rear chamber vents. Therefore, accurately and effectively grasping the effects of ventilation materials on the acoustic characteristics of in-ear earphones are currently the focuses of acoustic design. In this paper, a prediction model of the acoustic characteristics of in-ear earphones was constructed using the commercial finite element method software, COMSOL Multiphysics, and the changes in frequency response between the front and rear vents with ventilation materials of different specific airflow resistances. Finally, simulations were conducted to complete the study on the influence of ventilation materials on acoustic performance. The results showed that by importing the parameters measured using ventilation material measurement equipment, designed in compliance with international standards, into the validated simulation model, the effects of ventilation materials of various specific airflow resistances on the sound pressure level (SPL) curve can be effectively predicted after their attachment to in-ear earphone. In particular, with the measurement system and prediction model used in this paper, the error of frequency shift was controlled at 2% and difference in sound pressure value was controlled to 9%. In addition, by attaching meshes of different specific airflow resistances to the front and rear vents, the effect of the ventilation material was influenced by the Helmholtz Resonator effect generated by the chamber structure, which led to changes in the curve. The contribution of this paper is not only in the facilitation of the selection of ventilation materials for in-ear earphones in future designs, but also the selection of different types of ventilation materials according to the size of the chamber to achieve cost savings.