"Typical modern solid-state amplifiers with negative feedback tend to have high damping factors, above 50 and sometimes above 150. High damping factors tend to reduce the extent to which a loudspeaker "rings" (undergoes unwanted short-term oscillation after an impulse of power is applied), but the extent to which damping factors higher than about 20 help in this respect is easily overstated; there will be significant effective internal resistance, as well as some resistance and reactance in cross-over networks an speaker cables.[1][2] Older amplifiers, plus modern triode and even solid-state amplifiers with low negative feedback will tend to have damping factors closer to unity, or even less than 1 (very low damping factor/high output impedance amplifiers approximate current sources).Large amounts of damping of the loudspeaker is not necessarily better,[3] for example a mere 0.35 dB difference in real-life results between a high (100) and medium (20) Damping Factor.[4] Some engineers, including Nelson Pass claim loudspeakers can sound better with lower electrical damping.[5]
[Start Emphasis] A lower damping factor helps to enhance the bass response of the loudspeaker by several decibels (where the impedance of the speaker would be at its maximum), which is useful if only a single speaker is used for the entire audio range. [End Emphasis]
Therefore, some amplifiers, in particular vintage amplifiers from the 1950s, ’60s and ’70s, feature controls for varying the damping factor. While such bass "enhancement" may be pleasing to some enthusiasts, it nonetheless represents a distortion of the input signal."
https://en.wikipedia.org/wiki/Damping_factor