MIT Physics Demo - Barkhausen Effect
A soft iron core is placed inside a solenoid having several hundred turns of fine wire. The coil winding is connected to a loudspeaker. Audible results of the Barkhausen Effect are produced by slowly moving a permanent magnet toward the solenoid core. A loud rasping sound will be heard caused by the domains aligning themselves. Successive passes produce no sound until the polarity of the magnet is changed.
MIT Department of Physics Technical Services Group