8
Example:
A power amplifier has (at 1 kHz) the internal resistance
R
i
=
16 mΩ
The damping factor is then calculated to be 500.
Physical equation:
8 Ω / 0.016 Ω = 500 ***
This is a typical value for modern transistor power amplifiers.
(In comparison: at 1 kHz full tube power amplifiers usually have an internal resistance in the range of 0.4
Ω to 4 Ω
and therefore a calculated damping factor in the range of 2 to 20)
Technical background:
*
Loudspeakers do not have the same resistance at all frequencies. They are characterized by dynamic resistance, whereby the so-called
complex load is formed by the spring mass system, deflection and movement speed of the membrane, induced counter-voltage in the
voice coil, and crossover.
**
The internal resistance of a power amplifier is also a dynamic variable. It is only valid for a certain working point, with a certain frequency
and for a certain modulation. In addition, it can be determined in a number of ways.
*** These above-mentioned mathematical considerations do not take the loudspeaker cable resistance values or contact resistance (banana
connector, cable lugs, etc.) into account. In reality these loudspeaker series resistance values and contact resistance values are naturally
added to the internal resistance.
4. 2. 2 The technical part
As described above, due to the required high negative feedback reserve modern high power amplifiers with
transistors have very low internal resistance (
R
i
) and therefore high damping factors. These high damping factors
are desired because they have a very positive effect on important technical parameters, e.g. on distortion
characteristics.
At 5 kHz the damping factor of a power amplifier is relatively linear and has a high value, but then for physical
reasons (limitation of bandwidth) goes down with higher frequencies.
The degree and progress of the damping factor influence the in- and outswing behaviour and therefore the control
of the connected loudspeaker by the power amplifier.
4. 2. 3 Claims and reality
Claims are often made that a higher damping factor is better for controlling the loudspeaker and therefore the
system sounds better. This is not the case.
Correct is
that a power amplifier with a very low damping factor is not able to sufficiently control the loudspeaker.
It is, however, true that
a loudspeaker does not have the best outswing behaviour with the maximum damping
factor.
The truth
is that the value of the damping factor should in fact be within a certain range which is ideal for the
loudspeaker and should also be linear for as long as possible over the frequency range.
4. 2. 4 Solution: damping factor linearization
In order to meet these two requirements (ideal range and linear curve), in the switch position "
DAMPING FACTOR
- ON
"
we lower the complete value of the damping factor slightly to the ideal value and then linearize it over a
wide frequency range. In this process the advantageously high negative feedback reserves remain completely
intact (see text above). If the push switch on the rear is not pressed, the function is not activated. The absolute
damping factor is then maximized, but from 5 kHz decreases considerably. According to his preference, the
customer can choose to activate the damping factor linearization or not.
