Why would the point at which my amp clips change?

[Umbra]

This one's a bit of a headscratcher, at least for me.

The mystery: the point at which my sub amp clipped at a set volume (30/46) used to be .5 on the input sensitivity knob, but now I can max it out at .2 and it still does't clip.

My headunit volume goes up to 46. I chose to use 30 as the max volume because beyond that point the stock speakers attached to the HU would get too loud for me, but I still wanted to be able to max the bass by cranking up the level controller knob on the RCA cables going from the HU to the sub amp.

Last night I set the input sensitivity with the volume at 40 because I considered using no speakers powered by the HU - two amped speakers in the front and disconnecting the stock rear 6x9s. The point at which I saw clipping was around 1 on the input sensitivity knob.

I changed my mind and decided I still wanted the rear speakers, which are the only ones powered directly by the HU, so I wanted the max volume to be 30 again. I hooked up the front speakers and amp, set them appropriately, then went to the sub amp. Oscilloscope in hand, I set the input sensitivity like I did in the past: volume 30, 40hz test tone, EQs, balance, fade, and stuff off, zeroed, or neutral, but I didn't see any clipping at all this time, even with the input sensitivity knob maxed out. I turned the volume up a bit more and around ~35 the sinewave started to distort and the amp began to hum.

Now, when I first set the input sensitivity at 30 I'd used a CD as opposed to an iPod, I still had front speakers attached to the HU, and I had slightly thinner 4ga cabling (DB Link brand CCA - I've since connected that cabling to the speaker amp and bought Knukonceptz KCA for the sub amp), but I could've sworn I tried it last night with these same conditions and experienced it clipping around .5, like I'd been used to, but maybe I didn't.

What gives? Why can I push my amp harder now for some reason, could it be the better cabling? Things seem to check out on the oscilloscope.

I might just back off anyway because at full tilt I'm seeing interior lights dimming for the first time, but I wanted to hear what you guys thought.

Click to read more...

 

[Umbra]

bump

I don't even know how to search Google to answer this one, So I'm relying solely on the pros here at CA.

 

[bgowdy 5,000+ posts]

This one's a bit of a headscratcher, at least for me.
The mystery: the point at which my sub amp clipped at a set volume (30/46) used to be .5 on the input sensitivity knob, but now I can max it out at .2 and it still does't clip.

My headunit volume goes up to 46. I chose to use 30 as the max volume because beyond that point the stock speakers attached to the HU would get too loud for me, but I still wanted to be able to max the bass by cranking up the level controller knob on the RCA cables going from the HU to the sub amp.

Last night I set the input sensitivity with the volume at 40 because I considered using no speakers powered by the HU - two amped speakers in the front and disconnecting the stock rear 6x9s. The point at which I saw clipping was around 1 on the input sensitivity knob.

I changed my mind and decided I still wanted the rear speakers, which are the only ones powered directly by the HU, so I wanted the max volume to be 30 again. I hooked up the front speakers and amp, set them appropriately, then went to the sub amp. Oscilloscope in hand, I set the input sensitivity like I did in the past: volume 30, 40hz test tone, EQs, balance, fade, and stuff off, zeroed, or neutral, but I didn't see any clipping at all this time, even with the input sensitivity knob maxed out. I turned the volume up a bit more and around ~35 the sinewave started to distort and the amp began to hum.

Now, when I first set the input sensitivity at 30 I'd used a CD as opposed to an iPod, I still had front speakers attached to the HU, and I had slightly thinner 4ga cabling (DB Link brand CCA - I've since connected that cabling to the speaker amp and bought Knukonceptz KCA for the sub amp), but I could've sworn I tried it last night with these same conditions and experienced it clipping around .5, like I'd been used to, but maybe I didn't.

What gives? Why can I push my amp harder now for some reason, could it be the better cabling? Things seem to check out on the oscilloscope.

I might just back off anyway because at full tilt I'm seeing interior lights dimming for the first time, but I wanted to hear what you guys thought.

Really there are to many varibles to determine this. Voltage, rise, ohm load, HU settings etc

 

[Slobalt]

Did you change the wiring to your sub amp?

 

[bbeljefe]

iPod vs CD.

Either the track on your iPod isn't recorded at the same level as the CD you were using or the iPod isn't sending as strong a signal as the head unit is able to create with the CD.

 

[Umbra]

Really there are to many varibles to determine this. Voltage, rise, ohm load, HU settings etc

You're right, there are a lot of variables, let me address some:

I hadn't hooked up a volt meter, but in all instances the car would be at idle in the driveway, same battery, same alternator. I'm not dress what you mean by rise. Ohm load was the same in both instances, two dual 4 ohm subs wired to eight, then together so it's 4 again at the amp. The head unit is a fairly basic, single DIN Dual brand. All of the settings were defaulted.

Did you change the wiring to your sub amp?

Yes, the RCAs remained the same, but I redid the power and ground with a slightly beefier cable.

iPod vs CD.
Either the track on your iPod isn't recorded at the same level as the CD you were using or the iPod isn't sending as strong a signal as the head unit is able to create with the CD.

I was using a tone generator on the iPod, but I understand what you're saying. This would've been the first thing I would check but I thought I'd compared the two and got the same results, but I could be wrong.

Thank you all for the responses. The smart thing to do would be to go double check everything and start running comparisons. It's **** cold out, but I need some more info, so I'll go do that now.

 

[Slobalt]

you have your answers ^

 

[whitedragon551 5,000+ posts]

How do you know you were clipping?

 

[Umbra]

How do you know you were clipping?

40hz test tone and an oscilloscope. The waves would begin to square off, it seemed super simple.

I tried the 40hz test tone on the cd vs the iPod again. It looks like the cd has a slightly stronger signal, but not by much, at least it didn't seem like that was causing this anomaly. I think it's mainly got to do with the better power wiring and ground. The ground was secured in the same manner as last time, but with the slightly beefier cable.

Another thing I noticed out there is that I can't get the sine wave to square off anymore, at least not at volume 30 on the head unit. When the input sensitivity is low (turned high on the knob) the waves start to go jagged on the downslope. I suppose this is what distortion looks like.

 

[whitedragon551 5,000+ posts]

What DB was the test tone? Also you would be surprised at how people determine they are clipping. Most go by some sweet LED on some junk amp they have that they think is accurate.

 

[Umbra]

You know, I have no idea what DB the tones are.

I can't remember where I got the tone, I think it might have been Realm of Excursion, in which case it'd be 0 DB, but I can't be sure.

The app doesn't say anywhere on it, it's Tone Generator Pro. I'd guess 0 DB as there's no adjustment for it.

I'll make another disc for tomorrow with a test tone with a known decibel level and try that along with a different app where you're able to set the DB level as well as the frequency.

 

[Umbra]

I'm about to try setting the gains again with test tones recorded at known db levels.

What's the point of using a negative db tone? Is there a certain one I should use?

 

[calebkhill 10+ year member]

Music is not mixed at 0db. That's why using a -db tone gives you more output, you can go up on volume and gains.

-5db you should be safe.

Also, changing source units ipod/cd/etc, each device or source can clip at a different volume. That's why you need to test each source so you know the clip point.

Also, make sure your tone tracks are clean.