Nominal impedance
![Variation of characteristic impedance with frequency. At audio frequencies the impedance is far from constant and the nominal value is only correct at one frequency.](/Images/godic/202501/30/Twisted_pair_nominal_impedance.svg3103.png")
![Diagram showing the variation in impedance of a typical mid-range loudspeaker. Nominal impedance is usually determined at the lowest point after resonance. However, it is possible for the low-frequency impedance to be still lower than this.[19]](/Images/godic/202501/30/Speaker_impedance.svg3103.png")
Nominal impedance in electrical engineering and audio engineering refers to the approximate designed impedance of an electrical circuit or device. The term is applied in a number of different fields, most often being encountered in respect of:
The actual impedance may vary quite considerably from the nominal figure with changes in frequency. In the case of cables and other transmission lines, there is also variation along the length of the cable, if it is not properly terminated.