the main issue with doing it that way is the extra cost of cabling. it's really not the 'wrong' way, just not as cost effective as using a short length of wire to a solid chassis point.
while sean's setup will work fine with equally-gauged wires, it is also important to run at least 1 gauge larger(thicker wire) for the ground when using this method to try to reduce the resistance on the devices at the end of the wires.
Sean took what we call "The Boat" method. Even though in a boat you have to run a ground from the battery to wherever you are putting the equipment you have less chance of noise in a boat because you are surrounded by fiberglass. Fiberglass does not carry interference like a chassis of a car does. Not to mention the audio card or motherboard. Computers them selfs make noise which is filtered through the audio card.If that "filter" is no longer working correctly you will get noise. A four channel amp is the same way and is more sensitive to noise input through gain. Turning up the gain on an amp is not a volume control, it turns up the sensitivity on the input signal. I hope this has clarified things a little bit for you guys. If not ask away!
as long as you explain yourself
but i still don't agree with it.. you are either using the car for a large ground conductor, with a short length of thinner wire connecting the component to that ground point, or a long wire-- either still is bathed in large amounts of EMI--either from nearby devices outside the car, or emi from devices mounted within the car. i see your point about a single small cable having a higher chance of EMI induction from internal EMI sources within the car, but i really don't think there would be much of a difference because the smaller cable also can be better isolated from those EMI sources, where using the car chassis as ground can't be moved-- the EMI source needs to be isolated.
at least that is how it works out in my head..
the "noise" most people hear though those sources is most commonly a resistance to ground issue. A good resistance to ground to stay around and get no higher then .006 ohms. Depending on the wire used(oxygen free, copper plated, silver, short strand, long strand etc...) that plays a factor. So to eliminate or try to is to keep your grounds less then 18" long and ground in kick panel,rear strut towers,unibody, or to they frame it self. Then again it all depends on the car i.e. a corvette(fiberglass body and cast aluminum components).
sometimes noise can come from the power wire from it's self but there have been other times i've seen noise come from some of the newer cars ignition-system especially high out put . depending on the amp you can get noise. Lets say you use a good amp like a JL amp , i've seen people run rca's next to the power wire and have no noise at all. mean while i've had some alpines give me issues even when theres nothing around the RCA's . which also brings me to the type of RCA's used . a dual twisted is less susceptible to noise interference .Honestly i woudnlt have routed the ground from the battery i've been doing this for 8 years at least and i will always ground to the chassis of the body ex:trunk pan,factory bolt,etc. (of course wire brush first).i've always ran power on one side and input on the opposite side it's just how it's done in my opinion.
it can, but it's largely dependent on the quality of ground for the factory ground wire, and it's size-- if it's more than adequate for the factory equipment, and all you're adding is a carpc, then i don't believe there will be a noticeable difference.
if you're running a really large sound system--one that requires larger wiring then the factory ground wire uses, then it would help, but it would probably be best to consider the 'big 3' upgrade instead-- that includes beefing up the battery-to-chassis ground, as well as points like the alternator/battery connection, and the engine/chassis connection.
a power system is only as strong as it's weakest link, and the big 3 is a good way to minimize the weak links in wiring.
head unit of your car may be grounded to your vehicle firewall or to something behind your fuse panel, and its path back to the battery negative might be different than things in your trunk that are (hopefully) grounded to the floor pan of your vehicle. Changing the wire from battery negative to vehicle chassis will affect the physical path between battery negative and ground points for both devices equally...but may decrease the overall ground resistance between the two sets of devices as a percentage of total resistance both those devices represent when viewed as a load. In other words, it does nothing to solve the underlying problem, but it may help, indirectly, by lowering ground potential to all devices, the remaining difference between the devices being somewhat less when you express it as a percentage or fraction of the total voltage that should be available to those devices. Doing this can make your amps perform better, for example, and increase your signal-to-noise ratio across the board. HOWEVER, in my experience, the run from battery to vehicle chassis is usually very short, and an upgrade to even an extremely low gauge wire is unlikely to make a significant difference to ground potential difference overall. What I recommend doing is looking at the wire between your battery negative and your chassis...if it's longer than, say, 18 inches, or you suspect that it's not grounded particularly well, then you can look at ways of upgrading.
To truly eliminate the problem, especially in severe cases, requires first examining the physical ground path differences between devices, then addressing those differences. The approach most likely to work, imho, to eliminate differences usually involves several things. One is making sure all devices are grounded directly to large metal structures in the car that are uniform in nature, such as the floor pan of the vehicle, the vehicle firewall, or, in extreme cases (where differences in vehicle construction and weld points can make things in the trunk difficult to put on the same potential as things in the dash, for example) grounding everything to the actual negative terminal of the battery via a low-gauge stranded copper cable. The problem with even a low-gauge cable is that you often present more resistance to ground via a long cable run than the chassis/floor pan/firewall of the vehicle will, which results in decreased power available to all your devices, and possibly remaining noise resulting from potential differences being a more significant portion of overall voltage available. What this does give you, however, is a very predictable and controllable ground path scenario, where you can reduce or eliminate potential differences by simply varying cable lengths. In other words, you may be trading overall power available to devices such as amplifiers in exchange for putting all devices on equal footing and eliminating noise. Such an approach is often foiled by the fact that it can be difficult to put, for example, a factory vehicle head unit onto a thick copper stranded lead to ground.
The approach to try first, imho, is grounding all devices to the structure of the car, and making sure you have a clean metal-to-metal contact to some large piece of vehicle structure that's common to both devices, and that uses the shortest, most robust cable run from device to ground point possible. Remember, when you look at the metal of the floor pan, for example, as a conductor, it may be the equivalent of having an inches-thick cable for most of the run between device ground and battery. USUALLY, this is the best path, and imho, should be the first thing to examine in your setup.
Last edited by hithere; 12-12-2012 at 11:10 AM.
I have too much time and too little aggravation in my life, so I built a carPC. ;)