Damping factor
In typical solid state and tube amplifiers, the damping factor varies as a function of frequency.
Pierce[4] undertook an analysis of the effects of amplifier damping factor on the decay time and frequency-dependent response variations of a closed-box, acoustic suspension loudspeaker system.
However, it was also determined that the frequency-dependent variation in the response of the loudspeaker due to the output resistance of the amplifier is much more significant than the effects on system damping.
The calculations suggested that a damping factor in excess of 50 will not lead to audible improvements, all other things being equal.
is generally smaller than 0.1 Ω,[6] which from the point of view of the driver voice coil is a near short circuit.
In addition, the electrical characteristics of every voice coil will change with temperature (high power levels increase voice coil temperature, and thus resistance), the inductance of voice-coil windings leads to a rising impedance at high frequencies, and passive crossover networks (composed of relatively large inductors, capacitors, and resistors) introduce further impedance variations in multi-way loudspeaker systems.
In fact, the output circuitry of the amplifier will be the main electrical load on the "voice coil current generator".
If that load has low resistance, the current will be larger, and the voice coil will be more strongly forced to decelerate.
A high damping factor (which requires low output impedance at the amplifier output) very rapidly damps unwanted cone movements induced by the mechanical resonance of the speaker, acting as the equivalent of a "brake" on the voice coil motion (just as a short circuit across the terminals of a rotary electrical generator will make it very hard to turn).
It is generally (though not universally) thought that tighter control of voice coil motion is desirable, as it is believed to contribute to better-quality sound.
[citation needed] The voltage generated by the moving voice coil forces current through three resistances: This is the key factor in limiting the amount of damping that can be achieved electrically, because its value is larger (say between 4 and 8 Ω typically) than any other resistance in the output circuitry of an amplifier that does not use an output transformer (nearly every solid-state amplifier on the mass market).
Modern solid state amplifiers, which use relatively high levels of negative feedback to control distortion, have very low output impedances—one of the many consequences of using feedback—and small changes in an already low value change overall damping factor by only a small, and therefore negligible, amount.
Typical modern solid-state amplifiers with negative feedback tend to have high damping factors, usually above 50 and sometimes even greater than 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;[2] there will be significant effective internal resistance, as well as some resistance and reactance in crossover networks and speaker cables.
This load is moderately demanding but not untypical of high-fidelity loudspeakers that are on the market, and it is based on the circuit proposed by Atkinson.
In addition, the frequency response changes will depend on the frequency-dependent impedance of whichever loudspeaker happens to be connected to the amplifier.
Some amplifier designers, such as Nelson Pass, claim that loudspeakers can sound better with lower electrical damping,[12] although this may be attributed to listener preference rather than technical merit.
However, some speakers require an amplifier with a low damping factor to reproduce rich, full-bodied sound.
It enables choosing the speaker sound that one prefers.Damping is also a concern in guitar amplifiers (an application in which controlled distortion is desirable) and low damping can be better.
For instance the Marshall Valvestate 8008 rack-mounted stereo amplifier has a switch between "linear" and "Valvestate" mode:[14] This is actually a damping control based on negative current feedback, which is evident from the schematic,[15] where the same switch is labeled as "Output Power Mode: Current/Voltage".
