One of the best sounding speakers (touted by lots of audio affectionados) ...
http://www.stereophile.com/loudspeakerreviews/595/index.html
This is its response curve...
http://www.stereophile.com/images/archivesart/Mag16fig2.jpg

Another of the best sounding speakers in the world...
http://www.stereophile.com/loudspeakerreviews/920/index.html
This is its response curve...
http://www.stereophile.com/images/archivesart/WILFIG5.jpg

Neither are flat.