VoiceOver Speech won't change?

Hi there,

I have gone into the Speech section of the VoiceOver utility and changed every available voice to "Samantha". I then go into text edit to have a sentence spoken to me but when I tell it to speak, through Edit>Speech>Start Speaking, it's the default male voice which talks.

I've tried restarting the iMac but this hasn't worked. Any ideas whats wrong? If not, how about a way I can have a Siri-like voice speak a sentence? (I'm trying to make an animation based on Siri technology and just need a sentence or so spoken in her, or a similar voice)

Thanks for your time!