Ever notice how Batman, Spiderman, Superman and Iron man's voice changes when they're in super hero mode?

So I'm watching Iron man and as soon as Tony Stark (Robert Downey Jr.) puts on iron man, his voice changes into Mr. Cool, Calm, and totally collective, I'm most definitely gonna kick some mode! ( ^ _ ^ ) Just like Bruce Wayne. Once he goes into Batman mode? He's got this raspy, I'm gonna rip your head off mode. But the funny thing about Ironman, Tony Stark announces (Robert Downey) annouces that he's Ironman. So, why the voice change? Unless it's the armor? The acoustics in the armor?