Noise or distortion

[Taxed1]

Hello all. I was setting my gains using the cheap O-Scope method. I do own a DD1+ & a CC1. I was interested in seeing the actual sine wave so that’s why I got the cheapO scope. My amp is an SFB 2000. While tweaking the gain you can see those fingers at the top of the wave. Is that noise or distortion? Picture #3. I was not clipping yet. I was just below the clipping light on the amp. I’ve read some post that you can set the gains on these SFBs using the clip light but without actually seeing the wave, look at what you could possibly be sending to your subs. I settled with the 55 volts picture by the way. This was set while using a -7.5dB 40Hz tone.

On another note, the cheapo scope shows 55.16 volts but my Fluke TrueRMS volt meter reports 52.20 volts. Either way 52.20 volts = 2725 watts out of an SFB 2000!!!!????? The square root of 2725 = 52.20 volts, is my math right? Also, what about the oscope showing 55.16 volts of unclipped signal. That’s over 3000 watts right? I believe the Fluke more but still.

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[Buck 5,000+ posts]

That looks like a complex wave to me. It could very well be because of the amp and the type it is.

Question: was your vehicle alt on when you measured this?

 

[Buck 5,000+ posts]

This is very cool data, thanks for sharing.

 

[Taxed1]

That looks like a complex wave to me. It could very well be because of the amp and the type it is.

Question: was your vehicle alt on when you measured this?

Hello! Yes, the vehicle was on while setting the gains on the amp.

 

[Buck 5,000+ posts]

Hello! Yes, the vehicle was on while setting the gains on the amp.

I bet that's alternator pulsations going in through the DC power wires, the amp's power wires. In my opinion, what you're seeing is the alternator pulsations, because the alt pulses it's charging voltage, it's not really DC like a battery shows or delivers DC power. It's AC being turned into DC, so the DC still pulsates voltage like any AC generator would.

Many alts are 3 phase, like a 3 phase electric motor:

I bet you some money that your amp and it's lack of what seems to be capacitors (low dampening factor) is allowing the alternator pulsation to make it into the speaker wires, because the amp lacks the components to absorb these pulsations and smooth them out.

I think possibly a bank of very fast discharge capacitors or some type of lithium, that can hold a charge higher than your alt charges, would capture these pulsations and smooth them out, where your amplifier is feeding from less pulsating 12v current, aka a more consistent voltage feed into the amp.

I think this is what you're seeing in your wave there:

This is why I don't like those types of amps. It's the nature of lower quality amps, IMO. Amps with higher dampening factors and more internal components, all of those things are there for reasons, and it's largely about clean electricity and regulation of voltage spikes within parts of the system, whether it's the subwoofer and impedence changes, or if it's something like the alternator pulsations showing up in your actual subwoofer signal.

 

[Taxed1]

I bet that's alternator pulsations going in through the DC power wires, the amp's power wires. In my opinion, what you're seeing is the alternator pulsations, because the alt pulses it's charging voltage, it's not really DC like a battery shows or delivers DC power. It's AC being turned into DC, so the DC still pulsates voltage like any AC generator would.

Many alts are 3 phase, like a 3 phase electric motor:

View attachment 30880

I bet you some money that your amp and it's lack of what seems to be capacitors (low dampening factor) is allowing the alternator pulsation to make it into the speaker wires, because the amp lacks the components to absorb these pulsations and smooth them out.

I think possibly a bank of very fast discharge capacitors or some type of lithium, that can hold a charge higher than your alt charges, would capture these pulsations and smooth them out, where your amplifier is feeding from less pulsating 12v current, aka a more consistent voltage feed into the amp.

I think this is what you're seeing in your wave there:

View attachment 30881


This is why I don't like those types of amps. It's the nature of lower quality amps, IMO. Amps with higher dampening factors and more internal components, all of those things are there for reasons, and it's largely about clean electricity and regulation of voltage spikes within parts of the system, whether it's the subwoofer and impedence changes, or if it's something like the alternator pulsations showing up in your actual subwoofer signal.

Wow man thanks for the knowledge right there. I’m going to try looking at the wave again with the car off to see if it reappears.

 

[Buck 5,000+ posts]

Wow man thanks for the knowledge right there. I’m going to try looking at the wave again with the car off to see if it reappears.

PLEASE post those results up. I could be completely wrong, this guess just comes from studying electricity and atomic physics and such. I'm very interested to see about this; I know competitors who are shooting for 160 dB in the mid 20's and their systems are set up as much as possible to eliminate weird signals getting into the sub. Those alternators pulses will cause your amp to have to change amperage draw, depending on if you're at a peak or dip in the alternator pulsation, and that's some instability, to an extent. So, it's very possible you could lose a little SPL if your woofer is moving like some of the wave forms indicate, that you've shown.

 

[Taxed1]

PLEASE post those results up. I could be completely wrong, this guess just comes from studying electricity and atomic physics and such. I'm very interested to see about this; I know competitors who are shooting for 160 dB in the mid 20's and their systems are set up as much as possible to eliminate weird signals getting into the sub. Those alternators pulses will cause your amp to have to change amperage draw, depending on if you're at a peak or dip in the alternator pulsation, and that's some instability, to an extent. So, it's very possible you could lose a little SPL if your woofer is moving like some of the wave forms indicate, that you've shown.

I re-ran the test using the oscope with the vehicle off. Unfortunately the fingers / noise was still there on the scope. Honestly I believe the noise was more prevalent as opposed to the vehicle on. Pictures below. At the end I turned on the car and set my gains to 55.16 volts per oscope, 52.15 volts per Fluke. It is also possible the oscope is just a pice of crap.

 

[Buck 5,000+ posts]

I re-ran the test using the oscope with the vehicle off. Unfortunately the fingers / noise was still there on the scope. Honestly I believe the noise was more prevalent as opposed to the vehicle on. Pictures below. At the end I turned on the car and set my gains to 55.16 volts per oscope, 52.15 volts per Fluke. It is also possible the oscope is just a pice of crap.

Wow! It's doo no matter what! That's even worse than I expected lol! That's interesting man, thanks a bunch for posting that.

The lower voltage could cause distortion or whatever we're seeing there.

 

[Buck 5,000+ posts]

Does the wave, to you, look any better or worse? Or about the same?

 

[Buck 5,000+ posts]

I wonder if that wave issue could be the amp opening circuits in an un-smooth way, like transistors doing a harsh step up of power, and that's why you get the spikes at the top like that?

 

[Buck 5,000+ posts]

It could be impedance changes in the sub too, that could be part of it.

Sorry, haha, my brain is exploding, it's wants to understand this completely. That waveform looks like crap to me. It's like you have the frequency you're playing, and then some higher frequency intertwined with that frequency.

 

[Buck 5,000+ posts]

There's frequency modulation and there's amplitude modulation. You can do both and make a complex wave from that combo. Your waveform there reminds me of that somewhat, a carrier wave.

 

[Taxed1]

There's frequency modulation and there's amplitude modulation. You can do both and make a complex wave from that combo. Your waveform there reminds me of that somewhat, a carrier wave.

To be honest the sine wave looks better with the car on. Please keep in mind that while setting my gains the subs are disconnected. I am going to try to test the oscope on a couple of Skar amps I have in the closet, RP1500.1 & RP800.1 & see if the oscope is the problem or it’s just the SFB putting noise in the wave right before clipping.

 

[Buck 5,000+ posts]

Wait - is that device loading the amp?