Peter, our customers fancy amplifiers with a high damping factor. How high
should the damping factor be?
That's a matter of controversial discussions. Our Cable
and Damping Calculator gives you some information. To really understand
the subject we should first think about what damping factor means. I am giving
you a simple example using a subwoofer.
The following equivalent circuit will help to understand the interrelations:
Picture 1: Equivalent circuit: amplifier, cable and loudspeaker
are separated by green lines.
The damping factor D of an amplifier indicates how strong the amplifier's
output voltage is effected by load of the loudspeaker. The damping factor
depends on the impedance of the loudspeaker RL; from it follows that:
Well, I am now in a position to calculate the damping factor. But I can look
up this value in the technical data sheet that usually comes with an amplifier;
but what does it mean?
One has to look at it as a whole; the damping factor alone doesn't mean anything;
it can be calculated directly from the amplifier's output resistance Ra. For
the loudspeaker, however, the total sum of resistance Rges is important, comprising
the additional resistance of the cable Rk and the DC resistance of the loudspeaker's
voice coil Rs (the reactance L we neglect here to simplify matters):
In other words: if in both configurations (line 4 and 5 in the table) only
the resistance differs (resulting in a damping factor of 1000 or 200, causing
the loudspeaker's DC resistance to differ by barely 1%), then there won't
be any sonic difference.
But we can clearly hear that an amplifier with a high damping factor somehow
sounds more realistic and lively?
That's correct; but, there is a totally different reason for this. We have
to look at the bandwidth of the amplifier. The bandwidth is dependant on the
loop amplification g. The loop amplification g indicates how much more the
amplifier would amplify the voltage if there wasn't a negative feedback by
means of resistors R1 and R2:
Amplifiers with a high g also have a high bandwidth, since a phase stable
amplifier has to be designed in such a way that up to the cut-off frequency
g decreases by a factor of 10 (i.e. 20 dB) per frequency decade. (Here is
a PDF file covering the somewhat difficult Theory
1, the important diagram (picture 16) is to be found in Theory
In a nutshell:
By design, amplifiers with a high damping factor also have a high bandwidth.
This higher bandwidth results in the generation of more harmonics (by means
of noise and intermodulation distortion). This in turn is perceived by the
human ear as a particularly clear and crisp sound. Many recording studios
add harmonics by using an exciter (a professional device for sound enhancement).
However, the added effect should be subtle, otherwise the sound is just horrible.
So, a high amplifier damping of more than 100 doesn't contribute that much
to a clear sound as originally anticipated?
That's right; the damping factor should be around 100, but higher values are
not helpful in creating a realistic sound. Additional harmonics and noise
are in fact the determining factor in creating a sound that are perceived
by the listener as fresher, clearer, more realistic and believable, especially
in direct comparison.
And how do we get to absolute control given the choice of loudspeakers?
A loudspeaker should be chosen with a low total electrical loss Qeges. Basically,
a loudspeaker with a low electrical loss Qes is appropriate:
Which parameters do I have to pay attention to and are there any loudspeakers
with low Qeges?
The Q factor of the amplifier should be 100, the cable shouldn't have much
more than 0.1 Ohm DC resistance (for 8 Ohm speakers), otherwise a low Qes
for midrange and bass drivers are important. A low Qes can be found:
- especially for some midranges
- in large bass horns
- in specially tuned subwoofers, like Alcone Sub 10-60