The impedance of HI-FI speakers

Loudspeaker impedance is an aspect to be taken into account when installing an audio system. Electrical impedance measures the resistance that an electrical circuit opposes to the passage of a sinusoidal alternating current expressed in ohms (Ω). Unlike pure resistance, the value of impedance is not fixed and varies with frequency. For example, a hi-fi loudspeaker may have an impedance of between 3.5 ohms and 25 ohms, or even more at low frequencies, depending on the technology used.

The official standard, established in the 1990s, generally indicates 8 or 4 ohms in the technical specifications of hi-fi speakers, based on the speaker's impedance in the midrange at a frequency of 1000 Hz. However, this value gives only a partial indication, as impedance varies considerably throughout the audible frequency range. 

On the whole, it is reasonable to regard most current hi-fi speakers, including those from Focal, as having an average impedance of around 6 ohms. Modern amplifiers accept a range of impedances, but it is advisable to refer to RMS power over 8 ohms when assessing performance under difficult load conditions. This provides a safety margin in terms of available current. Focal distinguishes itself by clearly displaying the minimum impedance of its hi-fi products, thus acknowledging the diversity of the nominal impedance of 8 ohms, but an actual minimum impedance of 5 ohms.

Taking speaker impedance into account ensures compatibility between your speakers and amplifier, good frequency response and a balanced audio system where the impedance of the speakers matches that of the amplifier. This protects your equipment from potential damage.