Impedance in Car Audio Systems
If you already understand the “runes” on this amplifier back plate, you may already have the knowledge we are about to impart.
Impedance in car audio systems and audio in general is not that difficult to understand. However, there are pitfalls that can make uneducated meddling somewhat dangerous.
If you are up for an analogy then imagine I am pushing a shopping trolley while wearing roller skates. On a flat pathway with an empty trolley, my effort has only to fight the resistance caused by the weight of the trolley. There are other forces such as the friction between wheels, axels and path surface. When the trolley is loaded with heavy shopping (I like beer for instance!) then its resistance becomes greater. My task may become somewhat harder as a resul. My effort is less efficient, as the wheels on my skates prevent me from establishing traction. Put an upward incline in the way and I could be getting nowhere or even going backwards. Negotiating a downward slope, things could get a little or even very out of control.
This is a very simplistic non-scientific explanation of what impedance is.
If we translate this to electronic terms and the marriage of an amplifier (me) to a pair of speakers (shopping trolley), the perfect status quo is established when the impedance of the output is equal to that of the input to the speakers. Things get a little trickier when we discover that impedance is not actually fixed and changes with signal! You can think of the quoted impedance figure as an average figure if you wish.
Further translation should illustrate that when the speaker impedance is reduced, the amplifier has to do less work in order to create the same amount of sound. Many modern day car amplifiers use class D amplification. This is more tolerant to load impedance. We are able to deliberately reduce the impedance of the load (speakers) within strict parameters, in order to get more output.
Care must always be taken when doing this however, as the heavy shopping trolley that careers at high speed down a steep hill, will usually end with an almighty crash. In electronic terms this can result in smoke – Best leave it to your FOUR MASTER.
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