acoustic maculae

It was a lot of bonfires and acoustic guitar and kegs and all that stuff.

Harry would then ask himself if it was not the effect of some acoustic illusion, or some strange and fantastic echo.

Acoustic, a-kowst′ik, adj. pertaining to the sense of hearing or to the theory of sounds: used in hearing, auditory.

They are not responsible for any specific sound or acoustic feature of sounds except, possibly, accent or stress.

The anatomy of the vocal organs, and the acoustic and mechanical principles of the vocal action, are briefly described.

But how could a being without acoustic nerve and without a tympanum hear?