It's primary purpose is not sound deadening :
"The resonator is there to make more power and help the engine breathe more efficiently by dampening secondary and tertiary harmonic waves within the intake. Sound dampening is a byproduct of the increased flow efficiency. Air flows in waves, so there needs to be a Helmholz resonator in the intake track to allow back flowing eddies to dissipate, while allowing the bigger inflowing waves to maintain more of their velocity. The chamber makes the car run better."
"Adding an expansion chamber to the intake tube forces air coming back out of the engine to slow down to fill the cavity, thus expending a great deal of its energy and slowing the pressure wave reversion. This slowdown allows fresh air to flow toward the engine without fighting pressure reversion waves the entire way, thus aiding in cylinder filling. Since these pressure waves are essentially sound, giving them a place to expend their energy before exiting the air filter box ends up dampening the intake noise and quieting the engine. Thus, the resonator helps to make the engine paradoxically quieter and more powerful."