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John,I don't think you can infer there's an "ideal" damping factor.Since (in most cases) Zout << Rvc, "True Damping Factor" is essentially Zload/Rvc. Some speakers (as you mentioned) are essentially resistive, so the TDF is equal to 1.0. However, even for most of those systems, the crossover network probably creates a phase angle which skews the impedance relative to the Rvc in a part of the frequency range.If you're an amplifier manufacturer and want to advertise the output impedance of your product, you don't have much choice. You either have to express it as "damping factor" with a defined resistive load, or just quote the number directly. Bigger numbers look better so 100, 200, 1000, etc, is preferable to 0.001, 0.0153, 0.02, etc, ohms.I suppose the whole concept of Damping Factor as it relates to the amplifier/speaker interface is fairly meaningless. The speaker transducers are real-world, electro-mechanical devices and there's only so much effective "control" that a source could have on their operation.As Scotty says, it's an academic discussion.Cheers,Dave.
Steve, have you ever tapped the cone of a woofer with its inputs shorted, then open, and listened to the difference? I think the main interest in damping factor derives from the notion that all the drivers are under tighter control the higher the damping factor. I understand this to be one of the factors conferring superior performance (all else being equal) to active systems where there is a direct connection between amp and driver, where the crossover components are at line level before the amps and do not interfere with the amplifiers' control of the the drivers.
With resistive speakers like Maggies, which electrically approximates a resistor, the damping factor would calculate 8 DC ohms / amp output Z.
"True Damping Factor" is defined as Zload/(Zout + Rvc).
Um... not by the equation given earlier for "true damping factor":So you (Steve) appear to be using a different definition now. The conventional definition, in fact.Regardless, I'm fairly convinced the definition quoted above is wrong. You can't include the Rvc in the denominator, because of where you are measuring. (Sorry I know that's not very precise)
All about “damping factor”From the 1978-79Unabridged Dictionary of Electronics“damping factor”1] For any underdamped motion during any complete oscillation, the quotient obtained by dividing the logarithmic decrement by the time required by the oscillation.2] Numerical quantity indicating ability of an amplifier to operate a speaker properly. Values over 4 are usually considered satisfactory.3] The ratio of rated load impedance to the internal impedance of an amplifier.4] The ratio (larger to smaller) of the angular deviations of the pointer of an electrical indicating instrument on two consecutive swings from the equilibrium position.5] See “Decrement” Progressive diminution in the value of a variable quantity; also the amount by which a variable decreases. When applied to damped oscillations, it is usually called damping factor.6] The ratio of load or speaker impedance to the amplifier’s output impedance. Thus the smaller the output impedance the greater the damping factor. The damping factor increases with increase of voltage negative feedback, and with the large amounts of feedback applied to transistor hi-fi amplifiers the source or output impedance can be as low as 0.1 Ohm, giving a damping factor of 80 referred to an 8 Ohm speaker.Not that this is from 1978.
*********Frank (just home today after having left knee replaced)
