Red Dog Music | Oct 9, 2018 | 0
What is a damping factor and do I need one?
If you have a loudspeaker and an amplifier connected together, you already have a damping factor and it’s been getting on doing it’s thing, but what is a damping factor and how can it determine your setup?
When your amplifier sends a signal to your loudspeaker to make some noise, the speaker cone moves and pushes some air around to make a sound. Unfortunately, that’s not the end of it. After the speaker cone is forced away from its rest position it’s going to want to get back there, but it has momentum, so it overshoots on the other side. Near its resonant frequency, all this wobbling around can become quite pronounced.
This can often lead to ‘smearing’ of bass notes, as the speaker keeps moving around after the amplifier has told it to. To prevent this woolly softness and keep the bass ‘punchy’, this cone movement needs to be ‘damped’. The mechanical resistance of the speaker will take care of some of that, but can more be done?
So what is a damping factor?
Yes, there is more that can be done. If you think about it, there isn’t much difference between a loudspeaker and a dynamic microphone. So, when the speaker is moving, it’s also generating an electrical signal that heads back up to the amplifier in the same way that the diaphragm of a dynamic mic moves and generates a signal. This signal is called the ‘back electromotive force’ or back EMF.
The output stage of the amplifier presents an electrical load to the speaker, if that load is low, then there will be more current, which puts the brakes on that speaker movement and gives you that tight sound. An amplifier with a low output impedance in relation to the impedance of the speaker plus its cables presents such a load!
What does damping factor mean for my system?
With the very small output impedances of modern solid-state amplifiers, generally very little, you may not need to think about it. However, as damping factor is also affected by the impedance of your speaker cables, an investment in good quality, thick, low resistance speaker cables will reduce their impact on your damping factor.
Where things get a bit more interesting, is with valve amplifiers. As these are configured differently, and feature an output transformer, the output impedances are higher and therefore the damping factors are lower. But this may not necessarily be a bad thing, and the differences in damping factor are sometimes cited as being a contributor to the ‘valve amp’ sound, particularly when it comes to that most subjective of areas of sound- guitar amps…