Wind Noise Reduction In Cars
Wind noise reduction in cars is a complicated issue. With a car, we have a moving object that is full of “holes”. The holes are the seams of all the doors, the mirrors that stick out each side along with the engine, transmission, and tire noise. The trunk or rear cavity in the car is a resonating cavity that produces a sound of its own depending on its size. The molding around the doors and trunk lid do assist us with some reduction in noise transmission. However, there are just too many surface areas that require treatment to minimize noise transmission to really have the ability to lower noise levels to a point that we would prefer. Some makes and models do a good job of reducing noise transmission when they are parked and not moving. However, most of us want music and motion and having wind noise reduction in cars. Let’s take a look at all of the noise sources we are up against.
Noise transmission is all about vibrational acoustics. Noise is airborne energy that strikes a solid object such as our car. When the airborne noise strikes our car, it turns into vibrations that are then transmitted through the car structure. Our goal with any noise or barrier vibrational technology is to reduce the vibrational signature of the noise when it first strikes our car and is transmitted through the car structure. To illustrate this concept, we can use those off-ramps for trucks that lose their brakes on a mountain road. The truck enters the ramp and proceeds up the 45-degree angle of the ramp. As it moves up the ramp it bleeds off speed or energy and slows down so by the time it reaches the end, the truck has stopped. This is the same procedure we use with barrier technology to stop noise transmission. We make the noise energy travel through different layers of materials until it runs out of energy. By the time it reaches our ears inside the car, it is reduced in pressure below the ambient levels already within the car interior.
The engine compartment produces noise that is transmitted through the firewall. The engine compartment’s size determines the resonant frequency of the cavity. the firewall acts as a fire retardant along with a barrier for noise transmission. If you are really serious about wind noise reduction in cars, you pull the engine and fortify the firewall with barrier technology. This is usually not an option for most people when working on wind noise reduction in cars so we turn to the door seals. If your car is over 10 years old, you will need to replace these seals and moldings. Don’t forget the trunk moldings. Here are the products we have used successfully by Audiomute.
Once you have all the moldings replaced, you can then work on installing barrier technology inside the doors, floor, and trunk area. You will have to remove the seats and carpeting to do this process correctly. You need to use a mass loaded vinyl for this application. There are many types in the marketplace. Stay with a material that is at least 1/4″ thick. It is flexible and will mold to fit most locations. You can use heat on it to make it more pliable and get it to fit the contour of the car’s body. It is best to use another layer of a more dense substance between the vinyl layers. We have used MDF in some of our projects and created a “sandwich” of vinyl/MDF/vinyl. This multilayered approach will provide a vibration-reducing system that will minimize noise transmission.
Once you have the “sandwiches in place you will need to seal all edges of the “sandwiches” to make sure there are no air leaks. You need to view this procedure like you are building a boat that will eventually be placed in water. Any opening that does not have the same density as your sandwich will be a leak. You can use a spray rubber material as a sealer. In fact, you can use spray rubber as your first layer before you place your precut sandwiches onto the car’s surfaces. One product we have used successfully for many years is products by Flexseal. They offer glues and spray rubber compounds that are ideal for wind noise reduction in cars.
Doors are hollow cavities that resonant with air pressure placed upon them. The resonant at frequencies that are produced by the dimensions of the inside door cavities. The door cavities will first need to be sealed with mass loaded vinyl and then sprayed with liquid rubber to ensure all areas are sealed properly. Remember our boat analogy. The inside of your doors can then be filled with our carbon technology to absorb excess energy inside each door. Our carbon granules are placed in vinyl bags and secured against moisture. The bags of our carbon pellets are moldable and pliable so they can be pressure fitted inside the doors. Use 4-6 ounces of our carbon and create numerous bags that you can fit into the door’s inner chambers. These carbon bags will also act as a diaphragmatic fill material for your doors. A door is a diaphragmatic absorber that lacks the internal fill material which the carbon provides. This methodology will improve the bass response of the audio system.
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The truck or rear of the car is a large surface area that resonates with the size of the truck. Airflow over the trunk causes the trunk lid to vibrate. This vibration produces resonances within the truck. You must follow the sandwich approach we outlined above using the spray seal product line. You can then mold a fabricated shell of the interior of the truck which will allow for the same carbon bag technology as we installed within the doors. The prefabricated shell will serve as another barrier and with the carbon technology installed between the new trunk prefabricated mold and the sandwich layer, you will have a new trunk that will be a good barrier against wind noise in cars but also a good diaphragmatic absorber for low-frequency energy or “bass”.
The bottom of the car or undercarriage should be treated with vibration damping materials. The best solution to this issue is to use a spray material that will be water and heat resistant. A company called Ziebart has a spray vinyl that will work well for this application. It is a spray-on material that can be applied in layers to add additional mass to the undercarriage. It will also provide a rustproof layer that seals against moisture penetrating. This material will provide vibration damping along with rust protection. This treatment type is especially viable on cars that reside near the ocean and in areas that have salt on the roads to melt ice.
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