Impedance Bridging - Audio Amplifiers

Audio Amplifiers

In audio amplifer specifications, the value of the output impedance is sometimes described by the damping factor, DF, which is:

Here, Z_source is the output impedance of the amplifer. Knowing the DF, one can easily calculate Z_source:

Z_load is the impedance of a loudspeaker, usually around 8Ω nominally. The output impedance of the amplifier is typically in the same order of magnitude as the impedance of the cables connecting it to the speaker (<0.1Ω), so DF can be rather high, ranging into the hundreds.