Frequency Response Q

[D. Parting]

On this datasheet for the AKG C430(pdf) http://www.akg.com/mediendatenbank/psdoc/mediafile/74/import3fa2695c67fb6.pdf

There's the solid line, like I'm accustomed to. And the dotted line way below everything..... what's that mean?

 

[crazydoc]

You'll notice it says 180 degrees by the line - that's the frequency response from the rear of the mic.