Reducing Noise, Vibration and Harshness (NVH)

Not many people can afford a top of the line, luxury car like a Lexus, Mercedes, BMW or the like. But many would really like to have the ride comfort of such cars. These cars seem to just glide over road imperfections without jarring you. What is the secret? On top of having a suspension that is well tuned, many of such cars have automotive polyurethane foam in the hollow section of the cars.

The foam actually reduces noise and vibration by absorbing sound and vibration waves that travel up and down in the steel members of the car. Due to car chassis construction, with large thin metal walls, resonance occur within the car section like the A , B and C pillar, as well as doors and side sills. As the driver and passengers is surrounded in the car chassis steel frame, it is like a having a surround sound. But in this case, it is surround noise!

There are several types of automotive polyurethane foam. There are flexible foam, semi-rigid foam, rigid foam and finally structural foam. The first 3 types are designed to reduce noise, vibration and harshness and will not make the chassis stiffer. Structural foam will make the chassis stiffer. They have been used by car tuners to make the car handle better without adding much weight to the car.

However a word of warning. Before you go out and start pumping foam into your car sills and pillars, there are the correct type of foams and in-correct type. Do not, get DIY foam for your home. Only get automotive foam as there are formulated to cure in close air-less environment. If you use the wrong foam not designed for use in cars, you might just end up with a goey mass that you can’t remove.

Use structural automotive foam carefully because they will harden with a concrete like hardness. If you put them say in the B pillar, where there are electrical wires, the wires will be entombed forever with no way of getting to them for future repairs! Structural automotive foam should not be used in doors or other crumple zone as these members are designed to absorb energy in the event of a collision. Putting rock hard foam in these places might endanger your life. In such places, put either semi rigid or rigid foam non structural foam. These foam will absorb noise and vibration which is what you are after in the first place.

Lastly, test the foam on a soft drink can before you use them to gauge their expansion rate. Putting too much automotive foam in an enclosed space can result in the foam deforming your car, and we don’t want that to happen. This is especially crucial in car doors and C pillar where the metal is very thin.

Examples of automotive foam are Duramixand 3MA.

Another way to reduce noise, vibration and harshness is by using special foam to dampen them. This is not your normal packing foam but made to specially damper out frequencies found in cars that bothers the passengers the most. Purpose made for this include Dynamat. There are many good reviews from people who used it but installing it can take quite a bit of time. The upside is off course there is a huge reduction in noise, vibration and harshness.