Lexikon Impedanz specifications

Category : Lexicon

Also called impedance. It is the ratio between voltage across a component and the current through the component, expressed in the unit ohm. The impedance of a component or an entire circuit is usually frequency-dependent, which is why the specification of the frequency is usually additionally required. At the frequency 0 Hz (direct current), the impedance and (active) resistance are identical. With alternating current (frequency > 0 Hz), the effects of reactive (energy-storing) components such as capacitors and coils are added.

Because it is always confused:

Example: A commercially available loudspeaker with a nominal impedance of 8 ohms consists internally of several components, such as the chassis and (in the soft) coils, capacitors and resistors. These result in an active resistance, which can be measured with the ohmmeter in the case of direct current. The specification of the nominal impedance does not say that this active resistance is 8 ohms. It states that the impedance over the entire audio frequency range must not fall below the nominal impedance by more than 20%. But it can be arbitrarily much higher. To check this, you measure the impedance at all frequencies from 0Hz to over 20kHz, and create a diagram in which you apply the impedance over the frequency. The curve must not fall below 8 ohm - 20% anywhere.

It follows from this: The impedance cannot be measured with the ohmmeter, because this measures with direct current. An impedance meter measures with AC selectable frequency, and is therefore a more complicated and more expensive device.