Speakers in the size range of 1-5 mm are extremely limited, with common options being in-ear monitors and audiophile earphones, which may utilize small speaker elements. Ultrasonic speakers exist but typically do not cover the human hearing range needed for music or cellphone signals. The output amplitude of such small speakers is also a significant limitation. Hearing aids, while compact, generally target a narrower frequency range and may not meet the desired audio quality for music. Piezoelectric devices could be a potential solution, as they are designed for space optimization and can produce loud sounds within a limited frequency range.