It was such a curious corner in its acoustical properties, such a peculiar Ear of a place, that as Mr. Lorry stood at the open window, looking for the father and daughter whose steps he heard, he fancied they would never approach.
There are no more uses of "acoustic" in the book.
Show samples from other sources
She plays an acoustic guitar.
Then this guy—he couldn’t have been any older than Kyle—walked out onto the stage wearing a fedora and holding an acoustic guitar.