Phon.Audio
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Speaker

Damping factor

How tightly the amp grips the woofer — cable resistance counts.

Simple

How tightly the amp grips the speaker cone and stops it from ringing after the signal stops — think of it as electronic brakes on the woofer. Higher means tighter, more controlled bass; very low can sound loose or boomy. Your speaker cable counts here.

The theory

Damping factor is speakerImpedance / (ampOutputImpedance + cableResistance). A low amp output impedance lets the speaker's own back-EMF (the voltage a moving cone generates) be shorted out through the amp, electrically braking cone motion. The engine includes the cable's series resistance in the denominator — long, thin cable adds resistance and lowers the effective damping. ≥20 is tight; 8–20 is adequate; below 8 the bass control loosens.

For experts

The damping loop and why big DF numbers don't matterTop: the series loop the woofer's back-EMF sees — tiny amp output impedance, small cable resistance, and a voice coil resistance drawn much longer because it dominates. Bottom: response error versus damping factor, steep below 8 and flat beyond 20.Z out 0.05 ΩR cable 0.1 ΩR voice-coil ≈ 6.4 Ωback-EMF(moving cone)amp sideresistor length drawn ∝ resistance —the voice coil dominates the loop110100damping factor (8 Ω speaker)0 dB4 dB8 dBDF 8DF 20beyond DF ≈ 20 the curve is flat —DF 50 vs 500 differs by a fraction of a dBWorst-case response error from series resistance in the bass circuit, relative to an ideal amp

Here's the dirty secret the spec sheets hide: a damping factor of 20 vs. 2000 is nearly inaudible, because what actually matters is the total series resistance in the bass circuit relative to the speaker's own DC resistance — and the speaker's voice-coil resistance (typically 80–90% of nominal impedance) already dwarfs the amp's output impedance. Going from DF 500 to DF 50 changes the total damping of the system by a fraction of a dB. What genuinely moves the needle is cable resistance on long runs (which is why the engine folds it in) and tube amps with high output impedance (DF often 2–10), where the amp's output impedance interacts with the speaker's impedance curve to produce frequency-response bumps — that's an audible tonal effect, not a "looseness" effect. So the model's honest position: DF ≥8 is fine, the difference between "good" and "spectacular" DF is marketing, and the real story is impedance interaction, not cone grip.

DF=ZspZout+Rcable

Damping factor as the engine computes it — cable resistance included.

Rloop=Zout+Rcable+Rvc

The voice coil's own resistance dominates the damping loop — which is why DF 50 vs 500 is inaudible.

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