In general, when an electric field strikes a shield which is grounded the voltage which the field tries to create is drained away to ground and does not affect the conductors on the protected side of the shield. Shielding can be done anywhere, but is normally done close to the source of the noise or the device affected by the noise. In order for a shield to be effective it must be a good conductor, be well grounded, and have no discontinuities, such as openings or slots, in its surface. Grounding and Bonding In audio, technical grounding is connecting a circuit or a shield to the earth using a dedicated conductor. Bonding is connecting various elements of a system together, using low impedance conductors so that they are at the same electrical reference voltage - it is a reference common.
Grounding allows shields to work by draining away potentials.
Grounding and bonding means that any equipment which is referenced to it is at a similar, and likely stable, reference. Thus ground reference noise will not enter the system. In order for grounding and bonding to work well it must connect all equipment in a system together with a low noise and low impedance ground network which ultimate terminates to the earth. The connection to the earth should also be of low impedance. In order for the system to be low noise it is normally made of insulated conductors so that it is not shorted to other noise containing ground systems.