Acoustic radars

Acoustic mirrors, english south coast, 1920s

http://www.doramusic.com/soundmirrors.htm
http://www.ajg41.clara.co.uk/mirrors/dungeness.html
http://www.castlekas.freeserve.co.uk/sound_mirrors.htm
http://www.telegraph.co.uk/news/main.jhtml?xml=/news/2001/01/29/namp29.xml

Some more...



http://www.dself.dsl.pipex.com/MUSEUM/COMMS/ear/ear.htm