"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. While voltage-drives to speakers (reducing back-EMF from the speaker), i.e. high damping factors, are generally taken as a good design goal, there are some engineers who advocate low-nfb power amplifiers with damping factors closer to unity or find high Damping Factors have little effect, such as a mere 0.35 dB difference in real-life results between a high (100) and medium (20) Damping Factor. Really high damping requires a negative source impedance to partly compensate for the impedance of the voice coil.