Originally Posted by BerkTech

Those mysterious tubes? They're Helmholtz resonators. Their length/size orifice is tuned to resonate at a specific frequency which you hope is 180 degrees out of phase (opposite) of the sound you are attempting to attenuate. They can cancel out a specific sound or resonance. Think of it as a narrow band muffler with a high attenuation factor.

The next time you are under the hood of any car, look at the intake tract and you'll see an odd "box" hanging onto the intake tube that goes nowhere. It's also a Helmholtz resonator. If any of you work in an industrial setting, look at the exhaust outlets of your generator, boiler, etc. for an industrial sized version.