Part 1 - Electrical Noise
For the past six weeks you've worked relentlessly on the competition sound system in your vehicle. Your checking account is bone dry, and to top it off, your girlfriend is about to leave you for want of attention. In the past 72 hours you've redefined the word sacrifice. Lack of sleep has forced you into another dimension; a dimension where sight and sound take on new meaning. It's 6 A.M. and judging begins in just two hours. Final connections are made, equalization and crossover points are set, and a good balance of front stage - rear fill has been achieved. You reach for the keys and turn the ignition. As the engine purrs to life, a high pitched whine assaults the ears. NOISE!
Does this remind you of a nightmare you had one night after consuming a bottle of cheap wine and a pepperoni pizza? Nightmare or not, the above story is a true one that cost me first place and a five thousand dollar purse. From that day on I've sort of had a personal vendetta against noise.
For those of you who are wondering what noise is, I like to define it as any sound reproduced by the loudspeakers that is not present in the source material. Alternator whine, amp swizzle, ignition noise, turn on thump, and system noise are just a few examples that come to mind. In the following paragraphs I will outline each of these noises and the symptoms associated with them as well as some possible causes and remedies. Before we begin, however, let's review the TEN COMMANDMENTS of noise free installation.
The Ten Commandments
I. The best cure is prevention. I can't overemphasize this point. If you've ever spent an entire weekend tearing an installation apart in order to eliminate some noise, you know what I mean. Take the time to sketch the system out before you begin the install. This graphic representation of the installation will help you to avoid introducing ground loops and will serve as a road map for eliminating noise if it is present.
II. Don't introduce ground loops. Ground loops are created whenever an audio ground is established at more than one location. Theoretically, the only place the audio ground should be connected to the chassis ground is at the source unit. In my experience, I've found that in systems that have noise problems, a ground loop is the culprit nine times out of ten.
III. Never run signal wires alongside power cables. This is especially true in installations where high powered amplifiers are used. Large amplifiers are capable of drawing large currents. These currents vary with the musical demand of the program material as does the electromagnetic field surrounding the power cable. The more current that flows through the wire, the bigger this field becomes. If audio cables are located in close proximity to this fluctuating electromagnetic field, noise could be induced into the system.
IV. Always use 100% shielded audio cable. This will insure maximum protection against induced noises by power cables and other sources of electromagnetic interference. Good audio cables are not cheap. If you prefer to make your own cables, I would recommend using a wire with a foil shield surrounded by a drain wire.
V. Never use the ground wire in the vehicle's OEM radio harness. This wire usually makes a very poor ground due to it's length, small wire gauge, close proximity to other power wires, and unknown termination point. Instead, ground the source unit directly to the chassis or firewall.
VI. Make sure the amplifiers have a good audio ground reference. In order for the amps to function properly, the audio ground must be referenced to chassis ground at the source unit. If it is not, the amplifier could oscillate. To check for a good ground reference, take a volt-ohm meter (VOM) and measure the resistance between the chassis of the radio and the shield of the RCA line level outputs of the radio. This reading should indicate a direct short. If this is not the case, grounding the shield of the RCA line level outputs to the chassis of the radio will probably be necessary.
VII. Keep amplifier power ground wires as short as possible. The longer a wire, the more resistance it has. When a current flows through a resistance, a voltage drop is produced. Because of this, the ground reference at the amplifier's circuit board is no longer the same as that at the chassis of the vehicle. This ground potential differential can lead to noise and improper operation of the amp.
VIII. Don't connect all of your amplifier ground wires under one bolt. Contrary to belief, this is not required if the rest of the system is installed properly. If you do connect more than one power ground wire under a single bolt, you run the risk of amplifier ground modulation. This is caused by the current demands of, for example a woofer amp, modulating the power ground wire of a tweeter amp. This results in a squeaking noise that can be heard over the tweeters whenever bass notes hit.
IX. Make sure all levels are set correctly. Level setting is a critical part of the installation process. If done properly, maximum system signal to noise ratio can be obtained. Keep in mind that you want to drive the audio cables that feed the amps in the rear of the car as hard as possible. To do this, reduce the gain of the amplifiers to minimum. Turn up the volume on the source unit to 80% of maximum. Now adjust the input sensitivity of the amplifiers upward until the maximum intended loudness is obtained.
X. Noise filters can only reduce noise, not eliminate it. A noise filter is just that, a filter. And like any other filter (crossover network, etc.), it works by modification, not elimination. Some installers rely on filters heavily. In some instances a filter may prove necessary, but I believe that if the system is installed properly, a filter is usually not required.
About now most of you are probably making strange faces and saying "Now you tell me!" Well, all is not lost. If you have already installed your auto sound system and are unfortunate enough to have some noise, here are a few suggestions on where to look and what to do.
Alternator Whine
To me, alternator whine is the most annoying form of noise. For those of you who are lucky enough never to have been exposed to alternator whine, it sounds like a miniature siren that rises in pitch with the speed of the engine. Alternator whine is almost always caused by a ground loop. The following steps will aid you in locating and correcting a ground loop problem.
1. Verify that all levels are set properly.
2. With the system turned off, unplug the RCA inputs to the amplifier.
3. Start the vehicle and turn the system on. If the noise is gone go to step 8. If the noise is still present, it is coming from the amp or the speaker wiring. Continue.
4. Turn the system off and disconnect the speaker harness.
5. Start the engine and verify that no noise is present. In a few rare instances, I have actually heard speakers reproduce noise without being connected to an amplifier. This noise was being induced by power cables that were very close to the speaker wire. If you do have this type of noise, reroute the appropriate speaker lead and go to step 3.
6. With the speaker harness still disconnected, check to make sure there are no shorts between the speaker leads and the chassis of the vehicle. A shorted negative speaker lead will create a ground loop by establishing a second audio ground reference point. If you do have a short, trace the wire out and repair it then go to step 3.
7. With the RCA inputs and speaker harness still disconnected from the amplifier, use your VOM to measure from the shield of the RCA jacks on the amp to the chassis of the vehicle. This reading should not be a direct short (100 ohms or more is acceptable.) If this reading does indicate a direct short, you might have a defective amp and should contact the manufacturer for verification. (Note that there are a few "inexpensive" amps or boosters on the market that have their audio ground and electrical ground commoned internally. For units of this type, the information in this article will be of very little value.)
8. If you've made it here, you know that the amplifier and speaker wiring are okay.
9. Connect the accessories in front of the amp (crossovers, equalizers, etc.) one at a time and check for alternator whine. When each device is tested, there should be nothing plugged into the input of that device. In this way, we will work toward the source unit piece by piece. Be sure to turn the system power off before connecting or disconnecting any cables or accessories.
10. Repeat step 9 until all accessories have been tested.
11. If a particular accessory is causing noise, try disconnecting it's power ground wire. Go to step 9.
12. Now it's time to connect the source unit. Do that now and test for noise.
13. If noise is present, try unplugging the antenna. If the noise goes away, you will need to use an antenna isolator. This little gismo opens the shield wire of the coax to eliminate the ground loop caused by the ground at the antenna.
14. If you still have noise, try connecting the source unit's ground wire in another location,. preferably as close to the source unit as possible.
15. Does the noise vary in amplitude when you adjust the volume control? If it does, the problem is probably power line related and not a ground loop. If this is the case, run the source unit's B+ (yellow) wire directly to the positive terminal of the battery. If this doesn't do the trick, you will probably have to use a power line filter on the source unit's B+ (Yel) and Ignition (Red) wires.
Ignition Noise
Ignition noise is another type of noise that is quite annoying. It usually sounds like a popping or buzzing sound whenever the engine is running. The best cure is to remove the motor but since we can't do that, we will have to rely on some other form of remedy. Follow the steps below to eliminate or reduce ignition noise.
1. Make sure you are using resistor type spark plugs and resistor type plug wires.
2. Determine where the noise is coming from. If the noise is a popping sound that occurs 2 or 3 times a second, you probably have a loose or bad plug wire. First, make sure that all plug wires are seated properly. If this doesn't do the trick, you may have a bad plug wire. Usually this occurs due to a pinhole in the insulation of the wire. Whenever the plug wire is energized, an arc jumps through the pinhole to the chassis of the vehicle. Replace with silicone resistor plug wires.
3. If the noise is a buzzing sound, the problem is usually associated with the points, distributor, or coil. Try replacing the condenser on both the coil and points. Make sure all plug wires are seated properly in the distributor cap. Additionally, you might try adding a 2200 uF cap from the positive terminal on the coil to chassis ground.
4. Don't use the fuse block in the vehicle to derive power for the source unit. Run the Constant Hot B+ (memory) wire directly to the battery's positive terminal.
5. If you still have noise, it could be occurring because of induction. Try pulling the source unit out of the dash and check for noise. If the noise is eliminated, try rerouting any wiring harnesses that are close to the deck. If this is not possible, try using self adhesive metal shielding. This might just do the trick.
Turn On/Off Thump
Turn on thump can vary from a slight pop to a mind shattering, teeth rattling BOOM! This thump is caused by the audio circuitry stabilizing when power is applied. Most amplifiers and source units have muting circuitry that lasts a couple of seconds to allow these fluctuations to subside before passing a signal. However, if the amplifier un-mutes before the source unit or any other accessory, you better watch out. Here are some things to try if you have turn on thump.
1. Verify that the amp has a good audio ground reference. (See rule 6 of the Ten Commandments of noise free installation.)
2. Don't install the system so the amplifiers can be switched on when the source unit is turned off.
3. If you still have thump, add a turn on delay module in line with the remote turn on wire to the amp.
System Hiss
Hiss is usually most noticeable over the midrange and tweeters. The reasons for this are simple. The human ear is more sensitive to the frequencies reproduced by these drivers. Mids and tweets are usually far more efficient than their low frequency counterparts. And, these drivers are usually mounted closer to the listener. If you have hiss, you probably have your levels set improperly. See rule 9 of the Ten Commandments of noise free installation.
While I know that I haven't covered all the forms of noise or even all of the methods of dealing with it, I hope that I've made a good start. By adhering to the Ten Commandments and investing a little persistence, you will be rewarded with a noise free installation.
Part 2 - Increasing RF Reception
In the past twenty years or so, the auto sound enthusiast has experienced a quantum leap in the fidelity obtained from his or her sound system. During this period, head units have evolved progressively from primitive to today's state-of-the-art technical marvels.
Initially, AM radio was the only technology available. It's limited bandwidth, poor frequency response characteristics, and susceptibility to natural as well as man-made noises made for a poor means of transmitting high-fidelity sound. This, in conjunction with the spirit of free enterprise, paved the way for developing a better medium for broadcasting sound.
With the introduction of FM radio came a significant improvement in the fidelity of auto sound systems. Better frequency response, less noise, greater dynamic range, and stereo broadcasting contributed to make FM an almost overnight success. It wasn't long before most automotive sound systems boasted head units with both AM and FM reception capabilities. At this point, the demand for better quality sound began to snowball.
Innovation after innovation and breakthrough after breakthrough were soon made evident in the auto sound aftermarket. Clearly, a flurry of engineering, research and development, and marketing effort was being expended in tremendous proportions. Eight track tape players were introduced only to see their demise a few short years later with the introduction of the cassette tape player. Manufacturers were only too happy to oblige consumers with better and better sound. In short order, Dolby, Dolby B, and Dolby C were added to an ever growing list of features sported by most AM/FM Cassette decks.
The most significant advancement in high-fidelity auto sound source units came in 1984 with the advent of the automotive compact disc player. Random track selection, extremely high dynamic range, superior signal to noise ratio, flat frequency response, and low distortion are some of the features that made the CD player an audiophile's dream come true.
Since then, this trend towards space-age technology has continued at an ever increasing pace. It is interesting to note that in almost every instance, breakthrough improvements in sound quality have been accomplished by changing the medium in which sound is reproduced. Unfortunately, the AM/FM tuner portion of the source unit has been locked into the same particular format for almost twenty years.
Even though tuner design has been riding the same wave of technological advancement as that of the CD player, the same basic reception problems plague radio now as it did two decades ago. This is because the problems associated with high quality radio reception are located not internally, but external to the receiver itself.
Interference, both natural and man-made, is the primary cause of degradation. Since it is usually impossible to remove these potential sources of interference, it is vital that we take advantage of any means at our disposal in order to reduce interference and enhance our reception as much as possible.
The single most important component affecting reception quality is the antenna. This device, which is simple in concept yet complex in operation, intercepts incoming electromagnetic radiation that has been transmitted by the radio station. As the radiation comes into contact with the antenna, minute amounts of electrical current are induced into the antenna and the coaxial cable that links the antenna to the tuner. The tuner then amplifies these current variations and extracts the usable sound information.
Part 3 - Setting Gains
So many people have their amp gains set wrong, and to be honest setting them by ear is quite a crapshoot. Doing it properly with a multimeter is actually quite simple.
Here's how you do it:
Set head unit volume to 3/4 of maximum. Turn off all eqs/presets in the head unit.
DISCONNECT SPEAKERS
P = Power in watts
I = Current in amperes
R = Resistance in ohms (effectively the nominal impedance)
V = Potential in volts (Voltage)
Knowns:
Resistance (nominal impedance of your speakers)
Power (desired wattage)
Unknowns:
Voltage (we'll measure this)
Current
Formulas:
P = I*V (formula for power)
V = I*R (Ohm's law)
So after a little substitution to get Voltage in terms of simply power and resistance we get
V = square_root(P*R)
So, for example, say you have a 4 ohm load presented to a 150 watt amp.
V = square_root(150*4) = 24.5 volts
This means you should increase the gain until you read 24.5 volts AC on the speaker outputs of your amplifier.
As a source, use a sine wave recorded at 0db at a frequency within the range you intend to amplify. You can generate tones in cool edit or use a program such as NCH tone generator. (credit for NCH to imtfox, IIRC)
Additionally, you could use a scope to actually check if the signal is clipping, but I'm not going to get into that here as I doubt very few people have access to that type of equipment.
--------------------------------------------------------------
Offical dealer for the following-
SOUNDSTREAM
DB LINK
DB DRIVE
PANASONIC
GARMIN
ROSEN
SCOSCHE
XE DESIGNS
SOUNDGATE
PAC
LITEGLOW
very nice write up! sticky!!!
Good information, but you should credit the author. Posting copyrighted material is a violation of said copyright unless you've been given permission.
Labotomi wrote:Good information, but you should credit the author. Posting copyrighted material is a violation of said copyright unless you've been given permission.
permission given
--------------------------------------------------------------
Offical dealer for the following-
SOUNDSTREAM
DB LINK
DB DRIVE
PANASONIC
GARMIN
ROSEN
SCOSCHE
XE DESIGNS
SOUNDGATE
PAC
LITEGLOW
Awesome post. I'm sure I'll be reading it again after I screw up installing my sytstem.
Another call for this to be stickied.
good stuff, but youll never be free of all noise unfortunately
I think this is two stickies in one day. Good work.
Don't dig on the newb's sig!!!
hmmmm have i read that b4? you got permission from richard clark? know him do you? correct me if im wrong.
mecp certified installer#39272
great OLD read!
PRND321 Till I DIE
Old Motor: 160whp & 152ft/lbs, 1/4 Mile 15.4 @88.2
M45 + LD9 + 4T40-E, GO GO GO
wow i think this should be stickied as well great write up!
i didnt even notice that it was an old thread untill you mentioned it lol
click sig for my car audio videos
STICKY.
car audio noob since 1984.
Ya i know its old. I was trying to refind a video of a Cav walled with two 15 XXX's. I couldve swore it was Wysiwygs but I couldnt find it. Anyways I digress. I came upon this and thought it would be helpful.
Maybe Ill dig around some more.
Was it the yellow 03-05 cav? If it was then check You Tube for it.
This would be a helpful sticky.
Edited 1 time(s). Last edited Monday, May 18, 2009 10:09 PM
http://nwgme.org
Wysiwig had two XXX in a wall and hit 150.something, maybe 151. On a Term Lab mic.
There its is. Thanks much man.
