An Observation by Bach

[Bach] grasped the sound properties of any place at first glance. A remarkable illustration of that fact is the following: He came to Berlin to visit me; I showed him the new opera house. He perceived at once its virtues and defects (that is, as regards the sound of music in it). I showed him the great dining hall. He looked at the ceiling, and without further investigation made the statement that the architect had here accomplished a remarkable feat, without intending to do so, and without anyone’s knowing about it: namely, that if someone went to one corner of the oblong shaped hall and whispered a few words very softly upwards against the wall, a person standing in the corner diagonally opposite, with his face to the wall, would hear quite distinctly what was said, while between them, and in the other parts of the room, no one would hear a sound. A feat of architecture hitherto very rare and much admired! This affect was brought about by the arches in the vaulted ceiling, which he saw at once.

Hans T. David and Arthur Mendel, The Bach Reader: A life of Johann Sebastian Bach in Letters and Documents, 276. In Music of the Western World.