grounding lenght question

[fbi90909 5,000+ posts]

i am pretty sure this has been covered somewhere but I've been searching a bit and can not find much of any info on this.

well, what i am trying to get at is i know with most amps you are asked to use a ground of 2ft or shorter.

well currently i run a profile ap1040 for my stock speakers and they have always had a grounding noise, at first i thought oh maybe it's the head unit, it being a pioneer and all. did the grounding rca's and it still continued. initially i had the amp grounded to a seat belt bolt. yes it was properly sanded and such. later on in time i moved the ground and cut it shorter. currently it's only 1 foot and tapped onto the trunk floor into an area that seems to be the frame(unibody). it cut down the noise but i had kept assuming it was the head unit.

well! recently i was dicking around with the amps and i had disconnected all the RCA's from the amp and i was able to hear the noise coming out of my speakers. thus eliminating the thought of the noise coming from my rca's, and this was with the engine off and volume down, and no i do not get alt whine.

so well what i am getting at is-

if i grounded the amp directly to the battery am i able to go past the recommended shorter than 2 ft?

i have not unmounted my amp from it's place to test the ground direct which i will do in a moment but will it be okay to go above 2ft if it does clear up the noise?

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[ultimate157 5,000+ posts]

Running a ground directly to the batter is perfectly fine.

 

[fbi90909 5,000+ posts]

but the lenght of the ground is what i'm getting at. if it is grounded directly to the battery can it be longer than 2ft?

 

[helotaxi 5,000+ posts]

That "no more than 2' ground" thing is total BS not founded in fact. The ground still goes to the battery regardless of how you wire it. Ground to the chassis, the chassis is in the ground path and the distance that the ground has to go through the chassis is part of the total length of the ground anyway. Amp in the trunk and battery under the hood? Pretty much impossible to have a 2' ground now isn't it.

 

[audiolife 5,000+ posts]

odd soundstream recommends any amp that is "highpowered" to be grounded back to the battery....300w and less can be grounded in back.

 

[ultimate157 5,000+ posts]

odd soundstream recommends any amp that is "highpowered" to be grounded back to the battery....300w and less can be grounded in back.

Finally a company that doesn't recommend bad information. I'm not so sure about the specific 300w cutoff though.

 

[Tehgregzor 10+ year member]

Hay. Yay. You guys answered a question i asked in a previous thread. Thanks so much!

 

[fbi90909 5,000+ posts]

quite odd i must say about the ground lenght recommendations given by amp companies. lol, i just looked up in my manual for my saz, and it says to keep the ground as short as possible(not longer than 10 inches).

lol which in my system, the ground is actualy only 10 inches but is connected directly to the battery since the battery sits under it.

i'll start playing around with the amp today to see what i can get. it was dark last night so i didn't feel like doing anything.

 

[dragnix 5,000+ posts]

companies probably state as short as possible just because i'm sure some people out there just don't want to take the effor to run more than they would have to. So perhaps companies just try to make it simple for the users without having them messing it up. But yea, i ground straight to the battery //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[squeak9798 5,000+ posts]

The idea is to have a ground path with the least resistance. The 2'/3' rule is really just an arbitrary number that was essentially pulled out of the air.....no real basis for that specific length.

But the general idea is that the "wire" used for the ground from the amplifier will generally have more resistance than the chassis/body of the vehicle. So in order to have the least resistance, you would want to have the higher resistance medium (the wire) as short as possible and utilize the lower resistance medium (the chassis/body) as much as possible.

However the chassis/body can be a very poor conductor in some vehicles, which makes the use a dedicated ground wire back to the battery a better option. Also some people run large enough ground wire that the wire's resistance might actually be less than the resistance of the vehicle's chassis/body. I've seen conflicting reports on the resistance of vehicle's chassis.....some state it's equivalent to ~17' of 2/0ga wire, others state it's equivalent to ~17' of 4ga wire.....and both were reliable sources. But regardless, if the wire itself has less resistance than the chassis (i.e. if your vehicle's chassis is equivalent to 17' of 4ga wire in resistance and you are running 1/0ga wire), it's a better choice to run the wire directly to the battery. If the wire has more resistance than the chassis, you want to keep the wire pretty much as short as possible.

Or in your situation where the battery is located right near the amp, it's obviously wise to just ground directly to the battery.

 

[fbi90909 5,000+ posts]

Or in your situation where the battery is located right near the amp, it's obviously wise to just ground directly to the battery.

only the sub amp is located next to the battery which. the 4 channel is located an the oppisite side of the trunk.

good to know though.

 

[ultimate157 5,000+ posts]

They're both in the trunk, and so is the battery.

Assuming you ran your ground for the rear battery to the front battery, you will be making 4 unnecessary connections between the amp and the rear battery by grounding the amp to the chassis.

Assuming you ran your ground for the rear battery to the chassis in the rear, you are adding 2 extra connections between the amp and the battery by grounding the amp to the chassis.

Either way if you don't ground directly to the battery, then those extra connections could easily add resistance to the circuit.

 

[fbi90909 5,000+ posts]

right now it's rear battery grounded to the chassis with a 12" length cable.

battery sits directly above the ground.

sub amp sits right above the battery and is grounded directly onto battery with a 10" cable.

the 4 channel sits on the opposite side of the trunk which is being grounded onto the the trunk floor where it meets a frame like area that runs under neath the car.

well, after dicking around some and moving the 4 channel onto the location of where the battery is to ground it to the battery the noise still existed, but only from the front speakers and not the rears. at this point i really don't think it's the grounding but it could be the amp itself. i will switch the outputs on the amps on having the 1-2 channel come out on 3-4, and vise versa, to see if the noise is being conducted in the speaker wire or if the actual amp is causing the noise.

note: this is with the engine off and no RCA's plugged in. the amp itself is sitting on a thick towel so it does not come in contact with the trunk floor(no carpeting)

 

[ultimate157 5,000+ posts]

Run the 4 ch amp ground to the battery. Since the run isn't of significant length, there will be less resistance that way.

 

[fbi90909 5,000+ posts]

Run the 4 ch amp ground to the battery. Since the run isn't of significant length, there will be less resistance that way.

well, after dicking around some and moving the 4 channel onto the location of where the battery is to ground it to the battery the noise still existed,

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