Electrical characteristics of dynamic loudspeakers

The most common driver type is an electro-mechanical transducer using a voice coil rigidly connected to a diaphragm (generally a cone).

Other types have similar connections, though differing in detail, between their acoustical environment and their electrical properties.

At this frequency, the voice coil is vibrating in the speaker's magnetic field with maximum peak-to-peak amplitude and velocity.

The impedance reaches a minimum value, Zmin, at some frequency where the behaviour is fairly resistive over some range.

A speaker's rated, or nominal, impedance (Znom) is derived from this Zmin value, explained ahead.

Beyond the Zmin point the impedance is again largely inductive and continues to rise gradually with frequency.

This is the minimum value in the impedance vs. frequency relationship, which is always higher than the DC resistance of the voice coil, i.e., as measured by an ohmmeter.

A home hi-fi loudspeaker system typically consists of two or more drivers, an electrical crossover network to divide the signal by frequency band and route them appropriately to the drivers, and an enclosure that all these components are mounted in.

The electrical signal generated by the coil travels back along the speaker cable to the amplifier.

In practice, this is important to prevent ringing or overhang which is, essentially, a free vibration of the moving structures in a driver when it is excited (i.e., driven with a signal) at that frequency.

A properly adjusted damping factor can control this free vibration of the moving structures and improve the sound of the driver.