Acoustic Engineering

adjective describing something that cannot be heard

• The speaker's voice was so soft that it was almost unhearable in the large auditorium.
• I whispered a joke to my friend, but it was unhearable over the loud music.
• The sound of the car engine was unhearable with the windows rolled up.
• The truth was unhearable amidst all the lies and deception.

noun a part of the body that serves a specific function or purpose

• The acoustic organ in the concert hall produced a rich and full sound.
• I love the way the acoustic organ sounds in this room.
• That acoustic organ is really pumping out some great tunes.
• Her voice was like an acoustic organ, filling the room with warmth and melody.