What is it about the power wire that will put interference into a RCA signal wire? Is it the magnetic field generated around the wire with current flowing through it?
If so, then I wonder if it would be possible to cancel this out by running a ground wire along side of the power wire all the way back up under the hood like you were going to connect it to the battery also? The magnetic field around the ground wire would be much more concentrated than it would be on just the frame, and therefore, would react more equally to the power wire's magnetic field and stand a better chance of canceling it.
In a house, romex wire does not have any magnetic field around it due to the fact that the hot wire and the grounded wire are side by side. The wires carrying current in opposite directions cancel out the magnetic field. That's one reason they did away with single strand knob and tube wiring in houses from back in the 20's and 30's. Single strands of wire build magnetic fields, and of course this can build heat, which can burn down houses. Romex made it safer.
But whether it is AC or DC, it should still work.
AC, the current changes directions 120 times a second, 2 times being one full cycle of the sine wave, for a 60 Hz frequency. This makes no difference and still cancels it out since with both wires, the current is always in opposite directions no matter what point in the sine wave you are looking at, except zero of course, and then, for a fraction of a millisecond, you have no current at all, and therefore no magnetic field.
In DC, the current would never change directions and there would always be a magnetic field around each wire, but it would still cancel out magnetic fields due to the opposing fields with one going one way around the hot wire, and the other going the other way around the grounded wire.
OK, not that anybody would want to do this, of course. It would be pointless unless you just had no other way to run wires to the amp except on one side of the car only. But I was just thinking.....you know, what if.....and this came up.
I figured it would help people to better understand why to run them separate if they knew why it caused noise in the system, and not just to run them separately cause someone else said it was a good idea.
Replies (2)
swez on 02/7/2005 23:41:41
It is common knowledge that DC power from the BAT can contain some AC ripple noise on the line as well. The AC ripple is from using cheap diode bridges in the ALT. This gets passed to the BAT and right on down the line.
The major problem in noise cancellation, is to reduce any AC ripple currents that can be picked up by low voltage AC signal lines from the source unit. (Alt whine, spark noise etc.) Also, eliminating ground loops in the audio chain are key to noise free systems.
In a ground loop issue, the ground potentials between main power line feed, HU and amps/signal processors is/are paramount to a clean input signal to outboard amps. There can be slight deviations in ground potentials between power source, HU and amps. When this imbalance is great enough, we get noise. Why? Lack of noise cancellation, riding on a low AC signal source and we pick up AC noise, riding on the power/ground system. A braided pair of RCA's usually work better than side by side RCAs.
In most common practice, we keep the RCA (low voltage AC signals) well separated from DC power loops.
Make sense?
Swez
MrBrownstone on 02/9/2005 17:17:52
Basically, the alternator whine won't be picked up by your RCA cables or speaker wires...it'll be picked up by your headunit, crossovers, amplifiers, eq's and other pieces of equipment.
Cancellation works when something is out of phase (90 degree angle) and is not a factor in 12V DC. You can run wires on the same side or opposite sides...or just ground all of your components to the body of the car. Noise is a problem with the quality of the components not the wires.
Save the money on running ground directly to the battery. It hooks up to the body ground, and will pick up noise at the battery anyway.
If so, then I wonder if it would be possible to cancel this out by running a ground wire along side of the power wire all the way back up under the hood like you were going to connect it to the battery also? The magnetic field around the ground wire would be much more concentrated than it would be on just the frame, and therefore, would react more equally to the power wire's magnetic field and stand a better chance of canceling it.
In a house, romex wire does not have any magnetic field around it due to the fact that the hot wire and the grounded wire are side by side. The wires carrying current in opposite directions cancel out the magnetic field. That's one reason they did away with single strand knob and tube wiring in houses from back in the 20's and 30's. Single strands of wire build magnetic fields, and of course this can build heat, which can burn down houses. Romex made it safer.
But whether it is AC or DC, it should still work.
AC, the current changes directions 120 times a second, 2 times being one full cycle of the sine wave, for a 60 Hz frequency. This makes no difference and still cancels it out since with both wires, the current is always in opposite directions no matter what point in the sine wave you are looking at, except zero of course, and then, for a fraction of a millisecond, you have no current at all, and therefore no magnetic field.
In DC, the current would never change directions and there would always be a magnetic field around each wire, but it would still cancel out magnetic fields due to the opposing fields with one going one way around the hot wire, and the other going the other way around the grounded wire.
OK, not that anybody would want to do this, of course. It would be pointless unless you just had no other way to run wires to the amp except on one side of the car only. But I was just thinking.....you know, what if.....and this came up.
I figured it would help people to better understand why to run them separate if they knew why it caused noise in the system, and not just to run them separately cause someone else said it was a good idea.
Replies (2)
swez on 02/7/2005 23:41:41
It is common knowledge that DC power from the BAT can contain some AC ripple noise on the line as well. The AC ripple is from using cheap diode bridges in the ALT. This gets passed to the BAT and right on down the line.
The major problem in noise cancellation, is to reduce any AC ripple currents that can be picked up by low voltage AC signal lines from the source unit. (Alt whine, spark noise etc.) Also, eliminating ground loops in the audio chain are key to noise free systems.
In a ground loop issue, the ground potentials between main power line feed, HU and amps/signal processors is/are paramount to a clean input signal to outboard amps. There can be slight deviations in ground potentials between power source, HU and amps. When this imbalance is great enough, we get noise. Why? Lack of noise cancellation, riding on a low AC signal source and we pick up AC noise, riding on the power/ground system. A braided pair of RCA's usually work better than side by side RCAs.
In most common practice, we keep the RCA (low voltage AC signals) well separated from DC power loops.
Make sense?
Swez
MrBrownstone on 02/9/2005 17:17:52
Basically, the alternator whine won't be picked up by your RCA cables or speaker wires...it'll be picked up by your headunit, crossovers, amplifiers, eq's and other pieces of equipment.
Cancellation works when something is out of phase (90 degree angle) and is not a factor in 12V DC. You can run wires on the same side or opposite sides...or just ground all of your components to the body of the car. Noise is a problem with the quality of the components not the wires.
Save the money on running ground directly to the battery. It hooks up to the body ground, and will pick up noise at the battery anyway.
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