What exactely is clipping?

Mind_nl
10+ year member

www.bugfix.nl
clipping is if your sine wave goes out of range of what the speaker/amp can handle. The speaker will go up and down in a sin-pattern (pic1) If you increace the volume the wave will be bigger (pic2) causing the speaker to go up and down further. But the speaker can only go so-far. If you try to drive it further it will clip (top and bottom will be cut of) (pic3)

Well as far as I know thats it... someone correct me if I'm wrong.

BTW: feel free to use the picture in your own precentations/documentation as long as you DO NOT put my name with it //content.invisioncic.com/y282845/emoticons/wacky.gif.cf4a48f9e6dfe9504ffd2c946fd2f340.gif

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Shugarra
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Ummm, kind of close. Clipping is when the sine wave turns into a square wave, because you've boosted the power of the amp beyond the input voltage's capabilities, and the power output increases a great deal. The power increase can then, in turn, fry the voice coil of whatever you are powering and it also makes the music sound bad.

I know my explanation is worded kind of funny, but hopefully you get the point. Input voltage from deck is exceeded by output voltage on amp so amp tries to compensate and ends up creating a square wave which puts out approximately 30% more power than a sine wave which heats up the voice coil and could cause damage.

 

BDIDDY
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Sittin' Slick
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Let's say you're sitting in your car with the CD player on pause. You turn the volume up a considerable amount and when you press the play button the sub doesnt play till you turn down the volume. Is that clipping?

Thanks alot

 

helotaxi
5,000+ posts

Kilroy was Here
which puts out approximately 30% more power than a sine wave which heats up the voice coil and could cause damage.
The RMS power will increase but the peak will not and that is the problem. Think of an amplifier as a multiplier, because basically that is what it is. The scale of the multiplier is fixed. For example say the multiplier is 10 (it is not important to know what the factor is for your amp this is just a suppose). The input signal is 1 volt the output is 10 volts. Input is 2 output 20 and so on. There is a limit to this though. That limit is the rail voltage of the power supply. All the output devices do is modulate the voltage of the power supply. They cannot increase the the voltage beyond what they are given to work with. Say the power supply gives a 20V rail. That would mean that the top of the sinewave could be no higher than 20V. Assuming the multiplier of 10 again, the amp would be good up until an input of 2V. Beyond that input level the amp would no be able to reproduce the input signal accurately. Up to the 2V point it would be fine but beyond that it would just produce a 20V DC on the output until the input droped below 2V on the back side of the sine wave. The result is called clipping because if you look at the output wave form on an oscilloscope it looks like the nice pretty sine wave has had the top "clipped" off at the max rail voltage.

High power DC is very bad for the long life of speakers. DC is not creating movement in the speaker. It just goes to its limit and sits there. While it is sitting there with the cone pushed out or pulled in there is still current flowing through the coil. All that current is doing is generating heat, nothing else. With no movement to move air through the coil, the heat just sits there and builds up until bad things start to happen.

How do you keep your amp from clipping? Your deck puts out more than 2V peak and the multiplier is 10 and the max rail voltage is 20V so you are doomed right? Nope. Because there has never been a standard for the voltage of preamp level signals in a car, car amp makers have added a preamp stage to the amps to match the level of the source signal to the input level of the amp. This preamp is controlled by the gain dial on your amp. The idea is that the preamp section of the amp will adjust the signal level to one that the amplifier section of the amp can deal with without clipping. Your gain control is not a volume control (it can be used to lower the max level of the amp but not to increase it once the optimum level has been reached.) it is there to match the level of the preamp signal from your source unit to the optimum input level of amplification stage of your amp.

 

helotaxi
5,000+ posts

Kilroy was Here
Yep, sure can. Almost all HU's will clip their outputs before full volume. The top-of-the-line Rockford HU is advertised as never clipping but I'd wager that a bit-o-bass-boost would humble it. Adding any kind of boost (bass is the worst and loudness as well) will cause the outputs to clip sooner than they otherwise would. Yet another reason bass boost is bad.

 

tobz
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There is this thing called research, and helotaxi does it. It's how you learn stuff. And before you ask me, "how do I research then?". There is this magical place called google...

To google is a verb, familiarize yourself with that, and you shall learn anything you need to know, from wiring your car audio, how to build almost anything, how to fix your brakes, how to perform calculus to get something meaningful, how to use physics to help your problems, how to make tasty food, how to buy anything you'll ever need, and more...

 

helotaxi
5,000+ posts

Kilroy was Here
Helo, I'm curious how in the hell you know so much about car audio? I mean, right down to the physics of it.. what's your background?
I've been into this for about 13 years. I went to college to be a EE because I was very interested in it. That didn't work out (I wasn't too excited about the math aspect of the application of EE theory but I know the theory from personal reading. Hell, I used to read encyclopedias for fun, amplifier design books are much more interesting than those.). I retain knowlege very well and have excellent recall.

Do D class amps have the same switching as standard transistors ? If not then do you have to worry about clipping on them as well ?
They use MOSFETs rather than traditional transistors because switching speed is vital, but they can still be clipped. The amp will still try to multiply the signal by its factor and if that exceeds the max voltage then it just produces a pulse that is at its maximum voltage. Same limitations as any other.

 

homer3304
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Member
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midwest
helotaxi

I too am an ex EE major ( stupid math !!! ) //content.invisioncic.com/y282845/emoticons/confused.gif.e820e0216602db4765798ac39d28caa9.gif

So what is the hype behind the class D amps ? What do they do to get their efficiency ?

 

helotaxi
5,000+ posts

Kilroy was Here
Do you know anything about PWM power supplies? Basically that is all a Class D amp is. The switching is modulated to produce a semblance of the input signal at a higher voltage. They get their efficiency from the devices either being all the way on or all the way off. It is the partial on region of a transistor's range that generates all the heat and kills the efficiency.

 
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