Quote:
Originally Posted by Radio Wrangler
Let's shoot a sacred cow. What gets called Damping Factor in an amplifier isn't. If you designed an amplifier with zero output impedance, it would be as perfect a voltage source as you could want. It is impossible to dissipate energy in a zero resistance, so it CANNOT do any damping at all. THe damping of cone motion at resonances come from the resistance of the voice coil, crossover windings, wiring.
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I'm glad you pointed that out David. The impact of amplifier output resistance has almost no impact on a loudspeaker's performance.
It is one of the figures of merit quoted by amplifier manufacturers that isn't one at all.
From the guy who coined the term in the first place. He refutes this in a letter in August '47 WW
" Loudspeaker Damping"
IN your April issue D. T. N. Williamson refers to electromagnetic damping of a baffle- loaded loudspeaker, through low output resistance of the amplifier, as being important. I used to think so myself, and was the first to use the
word " damping factor " but my belief was much shaken by the following argument. If a loudspeaker can be represented by an equivalent circuit consisting of a resistance in series with an " ideal " loudspeaker of 100 per
cent efficiency, then the damping must be applied across the input terminals. In this case, even if the amplifier output resistance is zero, the damping is limited by the series resistance which, for 5 per cent efficiency, would be twenty times the resistance of the ideal loudspeaker. This extreme
simplification, of course, leaves out the reactive components of the speaker impedance, but the argument still holds qualitatively.
Can any reader of Wireless World point out any error in this argument? If it is true, there is very little gained by attempting to achieve excessively low output resistances.
F. LANGFORD- SMITH.
Sydney, Australia
Actually, following Small, the Q including amplifier output resistance includes a term in (Rg + RE) where Rg is the generator resistance AKA amp output resistance and RE is the electrical resistance of the voice coil (+ any crossover components). If RE is say 10 ohms and Rg is 0.02 ohms the effect of the amplifier output resistance is tiny (it makes a 0.2% change in overall loudspeaker Q!)
So the term "damping factor", as Langford-Smith realised 63 years ago, is a nonsense specification.
Craig