Inductors at audio frequency

Inductors at audio frequencies range in the value from few millihenrys up to about 1 H. They are always toroidally wound, or are wound in the pot core, or comprise part of the audio transformer.

Inductors can be used in the conjunction having moderately large values of capacitance in order to obtain audio tuned circuits. However, in the recent years, audio tuning has been taken over by the active components, specifically integrated circuits.

Inductors  at radio frequency

The radio frequencies range from 9 kHz to 100 GHz. At the low end of this range, inductors are similar to those at the audio frequencies. As frequency increases, cores having lower permeability are taken in use. Toroids are quite common up through about 30 MHz. Above the frequency air core coils are more frequently used.

In the radio frequency (rf) circuits, coils are connected routinely in series or in parallel with the capacitors to obtain tuned circuits. Other arrangements yield several characteristics of attenuation versus frequency, serving to let the signals at some frequencies pass, while rejecting the signals at some other frequencies.