Miniaturized Full-Range MEMS Speaker for In-Ear Headphones

This paper reports a highly miniaturized loudspeaker for in-ear applications. It is manufactured using MEMS (micro-electromechanical systems) technology, a technology that is well known e.g. from MEMS microphones and accelerometers. The speaker is based on a mechanically open design, featuring a perfectly decoupled piezoelectric bending actuator. To provide good acoustic sealing, the actuator is surrounded by an acoustic shield. Measurements performed on loudspeaker prototypes attached to an artificial ear simulator showed that despite the small size of only 2.4 x 2.4 mm^2, sound pressure levels of 105 dB can be achieved within the full audio range. Moreover, low total harmonic distortion (THD) of less than 0.4 % at 90 dB and 1 kHz have been observed.