According to the patent description that Apple has provided, a plethora of accessories provide voice recognition functions nowadays, but most of them have a flaw – they don't work well along with loud background noises. Enter Apple's invention, which intelligently detects the exact moment when the user starts to speak and uses dual high-precision microphones in each earbud that recognize the spoken phrases.
In addition, every time the accelerometer detects low-frequency signals (read: vibrations) coming from the user, one of the two microphones in each earphone will be steered towards any ambient background noise and eliminate it from the equation.
Bear in mind that most of nowadays' patent applications rarely leave USPTO's shelves, still, Apple's one is among the most plausible and realistic patent filings that we've recently seen.
source: USPTO via Apple Insider