unhearable
/ʌnˈhɪrəbəl/
adjective
- Impossible to hear; too quiet or faint to be perceived by the ear.
- The sound of the mouse's footsteps was almost unhearable to humans.
- The speaker's voice was unhearable from the back of the large auditorium.
- Some high-frequency sounds are unhearable to adults but can be heard by children.