Noise in a car stereo system is usually the hardest nut to crack and can be the most expensive.
The more noise, from both the road and the car itself, you rid your car of the better
your system will sound.
We will cover noise attenuation in two sections: External (road, wind, etc.) and Internal (ground noise, panel vibrations, etc.)
External Noise
The easiest to track down is external noises. Road and wind noises have very distinct sounds and can be found by just sitting in different positions while some else drives the car around town and you listen.
(For God's sake! DO NOT TRY TO FIND THEM WHILE YOU ARE DRIVING!!!)
Unfortunately fixing road and wind noise can be quite expensive. For instance, you find out your windshield has a small air leak and whistles when you get over 35 MPH. You would have to go to a specialist to have it properly
sealed to stop this noise. Other times, it can be very inexpensive to fix, like a torn windlacing on your door frame can be fixed many times with RTV silicone and stop a very nastly rushing sound.
I once fixed a window felt on a pickup for a buddy that when we put a meter next to it had a 103 dB whistle to it!!! It cost $20 bucks and an hours time to replace and the truck was darn near silent after panel treatment.
Road noise can also be coming through the panels of your car. As car manufacturers cheapen the manufacturing process, the sometimes cheapen the body panels wich cause two problems: panel flex (wich will be covered below) and road noise.
The easiest way to kill road noise is copious amounts of damping material such as B-Quiet, Dynamat, or Noise killer damping sheets. You can also find spray damping materials, foam, fiberglass insulation and even pillow fill useful in certain areas.
You can stuff every nook and cranny with fiberglass or pillow fill, it is cheap and can really quiet your ride down. Areas to consider doing this is A-posts, door posts, and rear quarter panels to name a few.
Internal Noise
Now, we are on to what can be the most irritating to track down and fix: Noise coming from the car itself.
Panel flex is caused when you take a relatively air tight (you did fix the leaks, didn't you?) car and introduce lots of air movement from the audio system in the form of bass and the panels give with the air pressure.
If panel flex is really an issue, by this I mean you can take your forefinger and flex the panel with very little pressure (Tin Can effect) then you may need to reinforce the panel with steel, aluminum or fiberglass ribs if space permits.
the most common area for this to be a problem is the roof and trunk lids. If you are a DIY kind but have never seen this being done, get professional help as this is a VERY involved process with the potential to ruin your interior and posssibly
void your warranty.
With that being said, if you are going to be doing the reinforcement yourself, you will need to remove the headliner or trunk lid liner and have someone stand outside the vehicle while you are inside it. Next, have them poke around the affected area
in order to find the points of greatest weakness. Mark these with a grease pen. When done marking, get a bunch of scrap lumber and scrap padding (carpet works well) and put props from the floorboard to these marks being careful not to pooch the roof outward,
just use gentle pressure. Now, have the person go back and try pushing again. You should see little or no flexing, if you do, mark the areas and prop them too, then, retest.
Once you are sure you marked all the problem spots, you should be able to connect them it some sort of geometric pattern and draw the lines. After you do that, you will want to install your bracing. There are more ways to do this than I can count but,
I will cover a quick few.
The most popular is steel rods covered with fiberglass matting to connect them to the panel. To do this, you epoxy 1/4" or 3/8" steel rods or 1/4" x 3/4" aluminum banding over the lines you just drew making sure that you have the clearance for this between the upholstery and roof.
Now, you will take resin and strips of matting and cover out to 3" to either side of the rods. Once this dries you should sand any protrusions so as not to puncture your headliner or upholstery. This process adds rigidity to the panel from the rods and
also from the fiberglass with spreads out the support of the rod. Once completely satisfied with the install, cover the entire panel with a damping mat or spray.
Another way to stop flexing is to cover the entire panel with alternating layers of damping mat and fiberglass. This is very effective but expensive. It can cost well over $500 to do it correctly on the roof of a four door car, but, the results are nothing less
than dramatic. Again, be sure to sand the whole thing down the smooth it out.
Another, more exotic solution, and probably out of the realm of the average Joe, is panel doubling. Yes, you read that right. I have seen a car where the guy had every panel that was reachable doubled with sheet steel by spot welding. The entire car had to be
sanded down and repainted. and it cost him almost six grand to complete!!! Needless to say the car was very stiff when done.
The last thing I will mention in this area is concrete. Yep! there are many extreme cars out there that have the body panels either filled or lined with concrete. This is only advisable for non-driven contest cars as you loose just about all function of the windows,
doors, and the car weighs about twice what it started out weighing. But, as you can guess, the cars are almost completely free of vibration.
Another area of noise that is a booger to contend with and, if left unchecked, can eventually ruin your system is Ground Noise.
Ground noise is best described by the whizzing noise you hear coming from your speakers when you hit the gas and it becomes louder and more high pitched the faster you go.
The first solution to this is making sure your connection to ground from your components is solid,
uses the same guage wire as the power side and is dedicated to audio components only. To establish a good ground find a very rigid point of steel within 3 feet of the amplifier or other audio component, making sure that you will not hit the gas tank, impede moving parts or hit electrical
wiring and sand away the paint and take a center punch and a hammer and dent in a spot.
Next take a self-tapping screw as large as will fit through your ring connector and a drill with a screwdriver bit and run the screw in at the point where you made the dent. After you have tighten down the ring connector(s), you will need to coat this with a clear coat of spray paint or
electrical sealing spray to prevent oxidation and help stop the connector from vibrating loose.
Once you are sure you have a good grounding point, and you still have noise, you may have a faulty component. If you think this is the culprit, have it checked by a technician and repaired if necessary. If not, then you probably need to add a ground loop isolator or a power filter.
Ground loop isolators are usually built into RCA cables and require very little effort to install over a regular set. Just follow the instructions that came with them.
Installing a filter requires cutting the power line and installing the filter inline. It usually consists of a large capacitor or, in some cases, a choke. Installation is straight forward and solves a lot of problems with engine noise.
While this section contends with a lot of the noise problem, you may find that none of these steps work. If this is the case E-Mail me for further help and I will try to assist as best I can without being there.
