Varying current in one circuit produces a varying magnetic field that in turn creates a voltage in that circuit or in an adjacent circuit. Inductance can create distortions in adjacent circuits (adjacent being close to one another and a circuit being a closed loop in which electric current flows). Inductance can be a problem particularly when speaker wires or interconnects run close together or in bundles placing the different circuits formed by those wires in close proximity. For this reason, cables should be shielded to prevent interactions and cables should cross at right angles where possible.