Damping Factor in Car Audio Systems

Damping Factor in Car Audio Systems

Damping Factor DF is:

DF=Zload/Zsource

(Wikipedia)

Many amplifiers carry a number for “Damping Factor” in their list of often unintelligible specifications. If you are of a mind to look at these when selecting an amplifier, how do you know what to go for? Is a high number better than a low number? what is the relevance and how is the performance of your overall system affected?

As always with these explanations, it is impossible for us to give you the whole university degree course and it is important that the reader understands that rendering highly complex concepts down to an easy to understand explanation can sometimes mislead. We feel however, that as Damping Factor is listed in a specification it is desirable to have at least a passing acquaintance with it! We start with some fundamental physics (again, heavily simplified). Everything has a resonant frequency. This is a fundamental frequency at which something wobbles when hit either physically or electronically. This principle is what makes most musical instruments work and is most easily demonstrable in the case of a guitar string. When a string is plucked it wobbles at a frequency determined by its tension, length, thickness etc. This is most desirable as the resulting effect on the air between the guitar and our ears is what we hear as sound.

Unfortunately, a speaker will also have a resonant frequency. This is undesirable as it means when the speaker is deliberately moved at its resonant frequency, it will falsely amplify it and also “ring on” after the impulse is removed – Only for a very short time but never the less this does affect the sound that you hear and is often an attribute of what is commonly described as “colouration”. Speaker manufacturers do their best to remove all traces of resonance from a loudspeaker through mechanical design of the basket, stiffness of the spider and even cone design itself amongst other things. Despite these efforts however, some resonance remains.

Is all colouration bad? That depends on a lot of things but apart from personal taste, it puts an element of sound at the hands of uncontrollable factors such as temperature. Control is everything and so damping resonance in many designers opinion, is vital! A speaker is a motor which works by harnessing more physics based around Electro Motive Force (EMF uh huh uh huh uh huh uh huh – Sorry!). Simply put, if you put a coil around a magnet and put electricity through it, the magnet will move, or at least try to. Similarly, if you move the magnet in an out of the coil it will create electricity in the coil. In a car audio system this means that any movement of the speaker voice coil feeds electricity back to the amplifier, potentially adversely affecting the integrity of the signal. Through careful design and over many yeas of creative design, amplifiers are able to monitor and overcome this effect and cancel out this erroneous movement and therefore control more precisely the movement of the speaker cone.

There are many parameters which affect this phenomena including the impedance of the voice coil, output impedance of the amplifier and the impedance of the wire that connects them. The effect is most apparent at low frequencies and a high number indicates greater efficacy. An Audison Voce Uno monoblock amplifier has a Damping Factor of 160. This is considered to be rather good!

We do hope this helps in some small way. As always, we would encourage you to put your car audio needs in the hands of a FOUR MASTER specialist who will be best placed to choose pieces of equipment that will work well together.

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