QuestionHello again, I had recently e-mailed about wiring 2 DVC subs and how my other subs had blown voice coils. I thought i understood clipping, but i was thinking of something else. Can you please explain to me what exactly it is? And are there any ways to prevent this, such as some type of gauge to inform me when it is occurring? Any help you could provide would be very much appreciated, again. Thanks again for the previous answers. Robert Simmons.
Answer
Hi again Robert,
Agreed, it is not uncommon for people to not see that they do not have 'strap their system to the electric fence' like poor Rambo, everytime they want to turn it up. Even more interesting is the fact that many have this exact thing happening far below maximum volume on the head unit!
This is not easy to fully explain since clipping occurs in different ways. The nice part is that the worst case (physical speaker clipping due to its' design limits of excursion which can get VERY audible. This is also referred to as 'bottoming out the voice coil') of clipping can be completely prevented by avoiding the 'primary' type of clipping, which occurs in the amplifier.
The signal that comes down the RCA jacks to the amp is a (small) sinewave. That is ..it looks sort of like an 'S' on its side.
Now try to stay with me here:
The entire function of an amplifier is to turn this small 'line level' sinewave into a larger (speaker level) sinewave on the output to the speakers. This basic amplification function is an increasing of the line level signal 'Peak to Peak Voltage'. So, it is turning a small wave into a larger one. Each amp is rated to tell you how much 'gain' you will achieve.
Ok..
As long as the gain structure of the system is set correctly (that is, all of the line level trim pot settings are properly set), an amplifier will always exactly reproduce our small wave into a larger perfect copy (with X amount of increased gain from a particular amp).
*The key words here are 'amplifier level trim pots' and their proper use and adjustment because if you set the inpiut level of the amp too high, it CANNOT reproduce the sinewave without 'clipping' off the upper and lower part of the sinewave when the amp reaches its rated peak power! This means that instead of going in and out smoothly, the speaker actually stops at that instant and waits for the INPUT signal to drop back down to a level it can accuately reproduce, THEN it goes back the other way and repeats... this can overheat a voice coil and HOW. A litle clipping will take longer to hurt the voice coil but still causes overheating and damage. There is a steady voltage (determined by the gain settings of the system) holding the speaker out of (or into) the enclosure during the clip. This is where the heat comes from. Avoid it at all costs. I hope this explains the clipping I am referring to.
I might add some basic gain structure pointers since you are probably going hummm about right now.
Before starting to set amplifiers gain, you should ALWAYS disable the bass boost if so equipped. also the head unit should be defaulted or 'flat' no bass/treble added or loudness on, no DSP's ect.... yet ;)
Crossovers built into amp method:
If dealing with multiple amps, I ALWAYS start with the mids/highs 1st, then add the Subs to match them (since in 95% of mobile audio systems, the mids and higs ARE the weakest link).
Put on a good quality CD. I use Pink Floyd Dark Side of the Moon for this reference, usually. EG Something you have heard on many different stereos systems that is dynamic and accurately reproduced. With amplifier(s) set to minumum, you then crank up the dead unit volume to about 90-100%... go to the amps and start bringin them up... the idea here is to have the head unit hittin hard as you do this vital adjustment. This way you are much less likely to have the amps set too sensitive right off the bat. See where I am going with this yet?? ;)
Go sit back up front and try the loudness.. at different volumes listen to some tunes.
The Bottom line is to be SURE you have the amps set so that if you do have the bass up a bit and crank the volume, you will not make the amp clip! This is then repeated for each amp in the system.
This gives you some system some well needed 'overhead', and will make things last dang near forever.
Tuff and often overlooked topic.. I hope this makes some sense of it, cause it is more than worth every single character I typed ;)
great question,
Jerry Mael
