# Checking for clipping, or close to it



## sqshoestring (Jun 19, 2007)

Is there any way to determine clipping from looking at RMS (or peak on a clamp meter) for an amp? I can scope it into clipping on a load, but that is not going to be the same as a sub right? I don't want to move my scope really, just wondered if I can get close with meters instead.

I'm trying to downsize my amp but want it large enough. The issue is these pyle subs like some other subs IB; they go to a certain xmax (around 1.125" total with a rule by eye) and with more power don't do much more. This is at 20-30Hz where they get the most xmax. I need the amp room and it would lessen the chance of toasting them if I ever got that rough with them, which I normally don't but just the same they should be setup properly. And, they are "1,000 watt" subs, that tells me little I can only guess they are then 500rms and so then 250rms when IB. That might be close, I know 175-250rms will xmax them out. With the 500rms alpine class D on them (a pair) now they don't bottom or anything, but I can see they will not exceed a certain xmax with more power. I don't think it is clipping but not sure. I measured that xmax on a 170rms rated amp on a sine through one sub and I don't think it had much more in it, but that amp was clipping some.


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## MarkZ (Dec 5, 2005)

You can, but it's a lot easier just to move your scope. Otherwise, you could try this:

1) using a test signal, measure the RMS voltage out of your head unit at each volume click (near where you suspect clipping to be, at least).
2) measure the RMS voltage out of your amplifier at each corresponding volume click.
3) plot the two against each other. (eg. HU voltage on the abscissa, amp voltage on the ordinate) Where the slope veers off is where your amp is clipping. It should be linear below clipping and sublinear above clipping.


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## sqshoestring (Jun 19, 2007)

MarkZ said:


> You can, but it's a lot easier just to move your scope. Otherwise, you could try this:
> 
> 1) using a test signal, measure the RMS voltage out of your head unit at each volume click (near where you suspect clipping to be, at least).
> 2) measure the RMS voltage out of your amplifier at each corresponding volume click.
> 3) plot the two against each other. (eg. HU voltage on the abscissa, amp voltage on the ordinate) Where the slope veers off is where your amp is clipping. It should be linear below clipping and sublinear above clipping.


Dang, I had calc and I didn't even think of that. I've watched amps clip on the scope and the RMS on the meter keeps climbing, but I didn't think of (plotting it and) looking at a change in the curve, makes sense it would taper off some.

Yeah it would be easier to use the scope, but would be nice to have other means in case anyone else on here ever has a need since most people don't have scopes....except that test would require some play time at max power, though I just need to do the subs.

I have no idea what power it runs, even pretty loud the amp only shows 10A draw but it goes up fast from there and I didn't check it when I was hammering on it. Right now it will toast the highs so I can't really play it that loud, but will change highs amp soon when I finally find some wire for my new blocks. And want to change all the rest of the drivers in the car, what a stupid idea... Anyway, I foresee running them harder in the future, on occasion, once the rest of it is up to par.


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## MarkZ (Dec 5, 2005)

If you had the right test signal, you could do it even easier. Instead of having to measure the RMS voltage of the head unit, you could basically define it by changing the amplitude of the sine wave on the test disc. So you could make a disc that has amplitudes like:

0dB
-0.5dB
-1dB
-1.5dB
...
etc

Or even finer increments.

Put each of those sine waves on different CD tracks. Then all you have to do is measure the RMS voltage at the amplifier for each CD track. Convert from dB to a voltage value and plot that as your x, and the amplifier voltage measurement as your y.


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