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Though "The Dark Knight" has been a bona fide cultural event, boasting rave reviews and boffo box office, it hasn't been immune to criticism. Some have quibbled with its political undercurrents, and others have criticized a muddled theme.

But here's the critique most widely held: Why does Batman talk like the offspring of Clint Eastwood and a grizzly bear?

Donning the costume for the second time, Christian Bale has delved deeper into the lower registers. As Bruce Wayne, his voice is as smooth as his finely pressed suits. But once he puts the cape on, the transformation of his vocal chords is just as dramatic as his costume change.

Particularly when his rage boils over, Bale's Batman growls in an almost beastly fashion, reflecting how close he teeters between do-gooder and vengeance-crazed crusader.

"The Dark Knight" hauled in $43.8 million to rank as Hollywood's top movie for the third straight weekend, fending off "The Mummy: Tomb of the Dragon Emperor" which opened a close second with $42.5 million. It has earned $394.9 million in just 17 days, according to studio estimates Sunday.

Though much of the voice effect is Bale's own doing, under the guidance of director Christopher Nolan and supervising sound editor Richard King, the frequency of his Batman voice was modulated to exaggerate the effect.

Critics and fans have noticed.

"His Batman rasps his lines in a voice that's deeper and hammier than ever," said NPR's David Edelstein.

The New Yorker's David Denby praised the urgency of Bale's Batman, but lamented that he "delivers his lines in a hoarse voice with an unvarying inflection."

Reviewing the film for MSNBC, Alonso Duralde wrote that Bale's Batman in "Batman Begins" "sounded absurdly deep, like a 10-year-old putting on an `adult' voice to make prank phone calls. This time, Bale affects an eerie rasp, somewhat akin to Brenda Vaccaro doing a Miles Davis impression."

Before the similes run too far afield, it's worth considering where the concept of a throaty Batman comes from.

In his portrayal on the `60s "Batman" TV series, Adam West didn't alter his voice between Bruce Wayne and Batman. Decades later when Tim Burton brought "Batman" to the big screen in a much darker incarnation, Michael Keaton's inflection was notably but not considerably different from one to the other.

But it was a lesser-known actor who, a few years after Burton's film, made perhaps the most distinct imprint on Batman's voice. Kevin Conroy, as the voice of the animated Batman in various projects from 1992's "Batman: The Animated Series" right up until this year's "Batman: Gotham Knight," brought a darker, raspier vocalization to Batman.

Conroy has inhabit the role longer than anyone else and though animated voice-over work doesn't have the same cachet as feature film acting, there are quarters where Conroy is viewed as the best Batman of them all certainly superior to Val Kilmer or George Clooney.

The animated series are notable because they drew on the DC Comics of Batman as envisioned by Frank Miller, whose work heavily informs "Batman Begins" and "The Dark Knight." (Bale and Nolan were unavailable to comment for this story.)

As Batman has gotten darker, his voice has gotten deeper. As some critics suggest, Bale and "The Dark Knight" may have reached a threshold, at least audibly.