One of the most critical things you can do for a car is to
sound proof it. Whether you have a Mercedes Benz, or a Hyundai Excel, all cars can benefit
from extra sound proofing (especially the Hyundai). The first thing to understand about
sound proofing is that it can never be accomplished in a car. The important thing is that
you can reduce the amount of external noise, and vibrations. Sound proofing will make any
car feel like a million dollars. A quieter ride, less distraction, and an overall more
comfortable environment are what you can expect when you start sound proofing your car.
For car audio enthusiasts, this topic is critical. Nothing will lose points faster, or
spoil your sound more than a resonating panel, or vibrating frame member.
Sound Proofing starts with some means of damping. A number of products are available for
this, and they all have various degrees of effectiveness. The best results are always
obtained from using a combination of these products. There are mats, sprays, foams, and
insulation available from a number of manufacturers
Mats are usually either Styrene-Butyadine-Rubber or asphaltic sheets backed with an
adhesive of some type (although other materials are used in some cases). Installing mats
in your vehicle is a simple way to reduce vibration, and is effective as well. The way
mats work is that they are used to cover panels. The material they are made of absorbs
vibrations in the panels, and turns them into heat, or it may simply lower the resonant
frequency of the panel. Mats can also be placed between panels to reduce the amount of
vibration between the two panels when they are in close contact. Many times, the mats will
also have a metal foil backing to improve the heat resistance of the matting (thus
allowing you to use it in an engine compartment). The matting also adds weight to a panel,
reducing it's tendency to vibrate in the first place. Some of the more popular mats are Dynamat and Road
Kill, but there are alternatives. One of those alternatives is a material known as
Ice-Guard. Ice Guard is normally used as a roofing material, but is essentially the same
material as commercial mats, except that it incorporates an asphalt material for water
proofing. Ice-Guard is much cheaper than the other commercial mats, up to 80% less. It has
to be bought in large amounts, however, and minimum purchases are usually 80 to 100
dollars for an entire car, compared to $400 using Dynamat or Road Kill. Ice-Guard also has
to be aired out for a couple of days after installation before you can put your interior
back in, and it is recommended that you spread some activated charcoal powder or baking
soda before laying your carpet back down over it.
Sprays are also used for damping. These sprays normally come in a professional can, which
require a compressor and paintgun to apply, but many companies are starting to market
aerosol cans of sound deadener spray. The spray is often used in places where matting
would either be too difficult, or would add too much weight/bulk. Door panels are the most
common application for sprays, as well as highly irregular crevices (like inside
kickpanels). Sprays are suitable for large panels as well, but they tend to be messy, and
require taping/masking off of upholstery and windows.
Foams come in two forms: Sheets of foam, and foam sprays. The sheets of foam are used much
like mats are; They are laid over panels to reduce and absorb vibration. Unlike mats,
which absorb the vibration and convert it to heat energy, foam sheets disperse the
vibrations throughout, reducing its total energy. Foam sprays are used to fill in
crevices. As they dry (or rather, cure), they expand slightly, pressing against the nearby
panels. The individual cells help to disperse energy away from the vibrating panel, and
absorb them. Foams can be expensive as well, and there is a low cost alternative here, as
well. The first is Styrofoam©, which can be obtained in a spray can. Styrofoam© is the
brand name for the polystyrene foam we are all familiar with (and somewhat annoyed by at
times). The fumes given off by Styrofoam© are noxious, and many communities have laws
banning its use due to environmental concerns. Another alternative is insulating foams
like Great Stuff©, which is used in home construction. Great Stuff© is cheap, fireproof
when cured, and readily available at any hardware store for about three dollars a can.
Great Stuff© is also shapeable when it cures, and can be used to smooth sharp corners.
The downside to Great Stuff©, like Ice Guard, is that it is messy. Once Great Stuff© is
sprayed on upholstery, your clothes, your skin, etc, it's all over. You hands will be
stiff and sticky for days, if not weeks, and your clothes are forever ruined. Great
Stuff© also expands voraciously, so spray it carefully.
Finally, there is insulation. Jute is the most common insulation. It is laid under carpets
in both cars and houses, and is basically a thick mat of fibers which absorb sound. Though
less effective than the other methods, it adds a plushness to carpets, and has very good
thermal insulation. Micro Jute is recommended, because it's much thinner than jute, and
has about the same level of effectiveness. Jute or Micro Jute can be gotten from a number
of manufacturers, and is available at any carpet supply store.
When using these methods, you will invariably use at least two, if not more. The one
opportunity I had to sound deaden someone's car for them (I did it as a favor, since it
wound up costing them about $250), was a 1986 Monte Carlo SS, which took me three days. I
used Ice-Guard all around the trunk, floors, side panels, rear deck, doors, and roof.
Great Stuff© foam was used in the less accessible A/B/C pillars, kick panels, inside
bottom of the doors, and rear fender wells. I used the foam to spot a few places in the
dash as well, such as the blower housing. I finished up with a layer of microjute on the
floor, rear deck, and lining the floor of the trunk. Some Dynamat
was used on trim panels because it was less messy. The reduction was incredible. The guy
for whom I did this first remarked that he wasn't sure his engine was started because he
did not hear it. He was also surprised at the quietness of the cabin, and compared it to
his wife's Lexus, which he said may not even have been as quiet. During driving, we
noticed a "whooshing" sound, which we traced to a defective door seal. We
replaced the seal, and tightened up the windows on day 3, and the car was as quiet as a
tomb at highway speeds, with only the sound of his monster exhaust making it through. This
car was a whim, for me, but it secured in my mind the importance of sound proofing to a
car.