#341805 - 03/12/04 04:57 PM
System Noise? Read This....
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DigitalBoomer
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This thread is being started as one to view if your are experiencing noise in your sound system. It is a fact that the automobile electrical system is one of the nastiest environments known to electronic equipment. There are three kinds of noise you can experience, thermal noise, induced noise, and noise caused by a ground loop. Thermal noise exists because mankind lives at about 300 degrees above absolute 0. It cannot be eliminated due to it's nature, but it can be minimized by carefully setting up your system to eliminate excessive heat. Good ventilation for your amplifiers and operating them within the limits recommended by the mfg. will minimize this kind of noise. It is the other two kinds that this thread will address.
Ground loops are insidious. Typically ground loops are created by a pieces of equipment having muliple connections being introduced into the system and being grounded at points of unequal resistance . Alternator whine is induced into the system because of this. Here are some suggestions for eliminating ground loops.
1) The "Big 3" Upgrade ( check out the sticky at the top of this section for detailed information ). This is essential because it allows you to insure that your system is getting maximum output from your alternator, but more importantly, it incorporates the chassis of your vehicle as the primary grounding terminal. The key here, as related to ground loops, is the battery's negative ground to the chassis, and the chassis ground to the engine block (the grounding point of your alternator). This should be completed using a gauge wire of equal or larger size than your primary power wire in order to eliminate a variation in resistance. Once you have completed this task you have now turned your vehicles chassis into a common grounding point for your systems components.
2) The Head Unit ground. The wiring harness attached to your factory HU should not be used to ground your new head unit. That harness is usually grounded to the dash along with all of the other electrical devices (turn signals, wipers, etc.) You need to run a separate ground wire (at least 16 gauge) from the black ground wire from the back of your head unit to a point on the vehicle's chassis. This ground point needs to be scraped and sanded to the bare metal. It is best advised to carefully drill a bolt hole through the chassis, scrape and sand both sides, and connect the ground wire using a ring terminal, bolt and nut, and lock washers on both sides to insure a good tight contact with the bare chassis metal.
3) Amplifier ground. Grounding a single amplifier should be a simple proceedure. Use a ground wire of equal or greater gauge than your amps power wire and ground it in the same fashion as mentioned above. When using multiple amplifiers you can use a common grounding point. This can be accomplished by the use of a ground distribution block where you connect the grounds of each amplifier to the block, then one wire of equal or greater gauge than your primary system power wire to a single grounding point. The key here is to make sure that the resistance of the grounding point is equal for all amplifiers. Some systems are more prone to noise than others. When you use a distribution block the ground currents of one amplifier may affect ground reference voltage of another causing the more power amplifier to dominate the ground. To eliminate this possibilty ground all amplifiers with their own connection to the chassis at points with 1/2 to 1 inch of each other otherwise the return currents that flow through the chassis may produce a noise voltage between the two points.
4) Capacitor ground. I will not address the whys and why nots of adding a cap to your system, that is another issue. The idea here is to treat the capacitor ground the same as you would an additional amplifier. Ground wire of equal or greater gauge than the power wire supplying the cap grounded to the distribution block or common grounding point as your amp or amps are grounded.
5) Additional component grounds. When you add processors, EQ's, DVD's, etc you need to keep in mind that by introducing them into your system you add the possibility of creating additional ground loops. They must be grounded with the same principles in mind as you would use in grounding the amplifier or head unit. It is okay for low-current components to share a common grounding point.
An important thing to keep in mind is that not all metal in a vehicle is electrically connected to the chassis. The frame or subframe is probably isolated from the chassis with rubber grommets and the connecting bolts may not be touching bare metal. The goal here is to ground everything back to the chassis using ground points of equal (or to within .25 ohms) resistance. If you are unsure of the resistance of a grounding point you can pre-test your grounds using a multi meter. Ideally you are looking for net values of less than 0.3 ohms. Use the battery negative as a reference and start by using a wire (any size will do) that is long enough to reach from the battery to the spot you want to test. Set your multi meter to ohms and measure the resistance of the piece of wire from end to end. Connect one end of the wire to the negative terminal of the battery and the other end to one of the probes on your meter. Use the other post of the meter to test potential grounding spots and write down the ohm readings of each spot. Subtract from that reading the resistance of the wire you previously measured and use the spot with the lowest resistance. You can check several spots and only ground in locations that are within .25ohms of each other if you have to use multiple grounding locations.
Finally we will address the issue of Induced Noise. Induced noise has a variety of causes. Induced noise is very sneaky. Sometimes it gets into your system through the power wire, other times it may sneak into the system via adjacent wires or other electrical components through electromagnetic interference (EMI). Here are a few ideas to help eliminate the sources of induced noise.
1) Power wire. It is commonly accepted that you run your primary power wire down one side of the vehicle opposite your RCA and speaker wires. You also want to run your remote turn on wire on the same side as your primary wire. The high current in the power wire creates a magnetic field that can induce noise into other wires in close proximity. Some consider this one of the false myths in car audio but in my opinion it doesn't hurt anything to play it safe and isolate the power wire.
2) RCA cables. It is not necessary to run out and spend big bucks on RCA's. Just make sure they are well insulated and have connectors that will make good snug contact when they are plugged in. Simple UTP cables (Unshielded Twisted Pair) are usually the best for car audio. It is OK for them to cross the power wire, just don't run them side by side. Install them in a way so they don't become pinched or cut. You may need to trim off excess cable and re-install the connectors to get them to fit. Excess cable laying around will induce loop noise. If you are using a 4 channel amplifier with 2 sets of RCA's you want to twist the two cables around each other from the HU to the amp. Ideally you would want to use a set of 4 channel (UTP) cables for 4 channel amplifiers to prevent loop noise from working its way in between the two sets of cables. If using an EQ or active crossover, do the same twist the cables from the HU to the component, then again from the component to the amplifier. One other thing to look out for is that some of your quality cables have large covers on the terminals that may need to be removed. If the connector cover comes into contact with the chassis of the amp, EQ, active crossover, etc. it will create a ground loop and introduce noise.
3) Speaker wires. Once again, it is not necessary to go overboard here either. A good quality 16/18 gauge for your speakers or crossovers and 12/14 gauge for sub woofers is all you need. Run them down the same side as your RCA's away from the power wire and install them in a manner that they don't become pinched when you put your vehicle back together.
4) Crossovers. These are one of the sneaky sources of induced noise. The inductors inside passive crossovers will pick up RFI. Keep them away from computers, blower motors, ignition wires, and each other. They will cross talk. You have to experiment with mounting locations to find the optimum location. Different crossovers have different size inductors so they can pick up different amounts of noise.. some can be mounted inches apart, some need half a foot or more. A simple way to test the crossovers is to connect a small speaker to the speaker output terminal on the amplifier and see if the noise is still there. If there is then the crossovers are OK and your problem exists somewhere back up the line.
5) Level Matching. Level matching helps eliminate hiss and lowers your systems noise floor. The manufacturers have provided level controls to allow the sensitivity of the unit to be adjusted to suit the requirements of the installation. Picking the proper operating level for a device gives you the best compromise between noise and headrom. From the amplifier's standpoint, the level control (or gain) should be set so that the amplifier is just short of clipping. Check out the post under amplifiers for proper gain setting to get more information on how to properly match the gain of your amplifier to the output of your head unit. Ideally you want a 3:1 ratio to establish the lowest possible noise floor. For example...if you HU has a 4v pre-amp output you would want your gains to be set at about 1.33v, a 2v pre-amp output you would set them at about .7v. Most amplifier gains can be adjusted from 125mv to 6v. Any time you have a noise issue the FIRST THING YOU SHOULD DO IS CHECK THE GAINS!!!
6) Ignition Wire - There are times when noise can be introduced into the HU through it's power supply. A simple check would be to connect the HU power wire directly to the + battery terminal and bypass the ignition. If the noise is eliminated then you can put a switch on the wire and use it or go to www.davidnavone.com and purchase a power wire choke or filter to install on the power wire.
Finding the Source. If you have done all of the above and still have noise you need to find the source. You can accomplish this by making a set a muting plugs. The web site listed above has a tutorial at the bottom of the page for making and using muting plugs. Take an old pair of RCA terminals and clip them off close to the end. Then take the + and - wires coming out of the plug and solder them together. Start at the amplifier and plug them into the RCA imputs. If the noise goes away then you have eliminated the amplifier, speakers, speaker wires, and crossovers as the source. If it is still there you need to check the amps ground, position of the crossovers, the intergrity of the speaker wires (crimped, or the wire may be exposed somewhere and touching metal) and the connection to the speaker. You can also connect a test speaker directly to each channel of the amplifier. If the noise is still present at the speaker located at the amplifier then you will know that the amp is the noise source. If the noise disappears then work your way back to the next component (EQ, active crossover, etc) then finally to the HU, checking the grounds along the way. If you isolate the HU as the source re-check the HU ground. You may find that the noise is being introduced through the power source. If that is the case try switching to a different source or connect the HU directly to the battery. You may even want to connect it to a battery not connected to your vehicle. You may also want to relocate the HU back to the amplifier using a set of jumper wires connected to the battery for your power and ground. Connect the remote wire and a short set of RCA's and test the HU at the amplifier. If the noise is still there then you will know that the problem is internal in the HU and it will need to be repaired or replace. If the noise goes away then the cabling or HU ground is defective. Finding and isolating system noise can be a cumbersome and time consuming affair. Hopefully this information will assist you in eliminating system noise.
Well there you have it, my contribution to helping you have a clean and (relatively) noise free install. The information contained in this post is a compilation from various articles from noted experts in the automotive audio field, interviews with audio experts, imput from competition level installers, and personal install experience. It is not intended to be the definative source for all noise issues. If the above suggestions do not eliminate your noise problems then I would recommend you take your vehicle to a professional install shop for more detailed troubleshooting and corrective action. You can also PM me if you have any specific questions. I welcome any additional ideas to this post... Happy Booming to all!!
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#341807 - 03/12/04 06:00 PM
Re: System Noise? Read This....
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Theshadow
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Good advice here! It would sure be nice to have a sticky on this one.
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#341808 - 03/12/04 06:21 PM
Re: System Noise? Read This....
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imtfox
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Originally posted by DigitalBoomer:
They are caused by the non-zero resistance of the wiring used to interconnect the equipment. Typically ground loops are created by a piece of equipment having muliple connections into the grounding system.
You don't need to have a zero resistance ground just equally good or equally bad grounds all through the system. Ideally, you'd want to have low resistance grounds all through the system, but they don't have to be perfect to prevent loops.
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#341809 - 03/13/04 04:43 PM
Re: System Noise? Read This....
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Stangeriffic2002
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Good post. A couple tips:
Ground loops are insidious. They are caused by the non-zero resistance of the wiring used to interconnect the equipment.
I'd also add that when wiring a component set, a lot of people like to put their crossovers in the doors/kickpanels. In my experience, almost every system where the crossovers were in one of these locations had noise in it. The reason for this is because crossovers are signal dividers, they carry signal just like a speaker wire or an RCA wire and therefore should not be placed near anything that carries power. In the doors you typically have at least ONE thing carrying power (lock triggers, power window wiring, heated mirror wiring, etc) and in the kickpanels there is almost ALWAYS a fuse box on one side or the other carrying TONS of power. The solution is to get those power sources as far away from the crossovers as possible by putting the crossovers somewhere else, such as underneath a seat or in the trunk with the amps. It's a lot more wiring, but in the long run it will be worth it.
Lastly, in many cars there is so much power being carried throughout the vehicle that there's no possible way to isolate everything carrying signal. If you have a vehicle like this or you are running power to multiple components (inverters, gaming systems, neons, leds, etc) and it gets in the way, you can cross the power wires as long as you do so at a 90 degree angle. Running signal parallel and close to power is what will create alternator whine and system noise.
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#341810 - 03/13/04 05:12 PM
Re: System Noise? Read This....
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DigitalBoomer
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Thanks for the imput, thread edited accordingly. There is another school of thought out there that says that running the power wire close to the RCA's and speaker wires inducing noise is a myth and should make no difference when using quality cableing. I would agree with Stangeriffic2002 and advise to run them on opposite sides crossing at 90 degree angles. Running all the wires together would make the wires hard to hide. Running them on opposite sides makes for a cleaner install. Since there are conflicting points of view on this subject one thing is sure, running them in this manner will not induce noise into the system.
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#341812 - 03/14/04 02:40 AM
Re: System Noise? Read This....
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Stangeriffic2002
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DigitalBoomer > Stangeriffic :p
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#341813 - 03/14/04 02:13 PM
Re: System Noise? Read This....
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bafk
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Would running the wire near the fuel pump is considered a noise source? I really think so from what I remember of electricity and magnetism in physic, a wire with some current running through it cause magnetic field "The right hand rule". But with the shielded RCA and a proper installation it is easily reduced
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#341814 - 03/17/04 12:50 PM
Re: System Noise? Read This....
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DigitalBoomer
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If you use twisted/shielded RCA cables the fuel pump should not cause any induced noise. One exception could be if you mount crossovers or line drivers in close proximity to the fuel pump. Just make sure they are a foot to 18" away and you should be fine.
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