It's How You Say It

Researchers have discovered that "the human voice, particularly changes to pitch and modulation, can betray the speaker’s hidden sexual attraction to his or her listener".

not only do men’s voices get deeper when they’re chatting up some lovely woman, but they also get higher compared to when their speech is directed at another male or to an unattractive female listener.

A low-pitched voice signals masculinity, while a sing-song modulation lessens the fear that the speaker is overly aggressive.

In other words, “Hey, sexy lady, hear this? Hear how I’m sounding right now? That’s right: I’m a virile, testosterone-fuelled male specimen of our species but, cross my heart, I’ll be sweet to you… and our future offspring.”

The math: Deep voice + modulation = Masculine + non-threatening = Sexy

If guys say it right, it doesn't matter what they say or even how they look. Below is an example from one of the all-time greatest practitioners of vocal seduction.