Consumer Electronics

DYNAMIC LOUDSPEAKERS

There are two varieties of dynamic loudspeakers : electrodynamic and permanent magnet (PM) speakers. Both work in exactly the same way, the difference is in their construction.

The electrodynamic speaker has a soft iron magnetic circuit, non-retentive of magnetism, around whose centre leg, a large, multilayer field coil is wound, as shown in Fig. 4.7. When dc flows through this field coil, it magnetises the iron core. A magnetic flux field directly proportional to the strength of the current through the coil is thus set up across the airgap. The iron core is not permanently magnetised, it stays magnetised only as long as current flows through the field coil.

 

 

Fig. 4.6 A two-way electrostatic utilising a separate woofer ...