Sound Engineer's Pocket Book, 2nd Edition

12  Loudspeakers

Figure 39  Basic elements of a moving-coil unit

The magnitude of the force on the coil is given by

F = BIl newtons

where B is the flux density (Wb/m²), I is the current (A) and l is the coil length (m).

The velocity of the coil/cone is found from

ν = F/Z m/s

where F is the force (N) and Z is the mechanical impedance (mech. Ω).

Figure 40  Basic magnet configurations: (a) conventional central ‘pot’ magnet; (b) flat shape used with ceramic magnets

To avoid distortion with large amplitude signals, and hence large coil movements, ...