Enhancing your car audio stereo system can cost a pretty penny, and what most people want in return for that hard earned money is superior sound quality. Good quality amplifiers, subwoofers, and speakers all improve the quality of sound your vehicle’s audio system produces, however, they do not eliminate unwanted sounds such as road noise or rattles your car may make.
Getting a handle on that exterior noise can be as simple as installing sound deadening to eliminate the excess vehicle vibration and engine clatter. Most car audio experts recommend adding sound deadening (or damping) equipment to your vehicle because it optimizes your sound system.
One issue that is prevalent in cheaper cars and other older vehicles is the shakes, rattles, and road noise that you are forced to experience on nearly an everyday basis. This is caused by cheap hard plastic material getting loose over time from regular vibrations and bumps with little to no damping to stop the rattles. These rattles most commonly occur in areas such as door panels, the dash, and trunk lid.
Car doors themselves are not very good speaker enclosures, given that they are constructed from thin, hallowed out sheet metal. The poor acoustic environment results in discordant speaker rattling and vibration. Sound dampening eliminates negative wave cancellation, when the sound bounces off parts of the car before racing your ears, which reduces volume output and clarity.
Adding sound deadening will not only reduce the shake, but by taking up that extra room in the panels of the car – it will fill up the “space,” make the panels more rigid and less flexible which cuts down on the room the sound has to bounce around and lose quality. It’s difficult to measure the square footage needed to cover your car. There are specific kits made for your whole vehicle, which are usually called “bulk packs”, and kits made specifically for your trunk, doors, floor, roof, hood, speaker panels, and even license plates. It comes in many different sizes and thicknesses based on what you’re going to use it for. The most common form of sound dampening material comes in sheets or strips and is applied with an adhesive on the back of the sheet for installation that is then rolled on with a special tool.
Adding sound dampening layers to your panels is the non-electrified version of amplifying your system, because it creates an environment for a purer sound stage. Sound deadening materials are typically weather and temperature resistant, which ensures you will enjoy premium sound quality for many years to come.
- When installing sound deadening material, take a spin around the block in your car with the radio off to see where the most unwanted noise or rattles are coming from. The main places the annoying rattles come from are the vehicle’s floor, wheel wells, firewall, doors, roof of the trunk, and under the rear seats. Refer to your vehicle’s service manual for information on how to dismantle the trimming panels. Be careful when removing the panels to avoid breaking the fixing clips.
- Once the trimming is dismantled, remove the remainder of the factory insulation if it is damaged. If it is still intact, there is no need to permanently remove it. Next, you need to properly clean, dry and degrease the prospective surface. Sound deadening won’t adhere properly if applied to a wet or dirty surface. Use a metal surface cleaner or degreaser along with a dry, clean rag. Make sure to use gloves and apply the degreaser in a well-ventilated space.
- Measure the prospective surface you are going to treat. To make things easier, make a template on a large sheet of paper and then transfer it to the damping material. That will make it easier to install it more accurately and avoid wasting material. Use a utility knife to cut the desired shape and size.
- Place a sheet of sound damping to the surface without removing the protective film. If it covers the surface properly, you are ready to install it. Gradually remove the protective paper film as you apply it to the surface for better adhesion. Once on the surface, press it down firmly until it is set in place. Flatten it with your hands to avoid unnecessary air bubbles. Use a rolling tool like the NVX SDRLR2 to press the mat down to the metal surface. Go across the entire surface with the roller to ensure that the sheet is installed properly.
- Once all sound dampening is in place, simply reinstall all trim pieces and carpet back to its original placement. Now you are ready to enjoy higher sound quality with fewer vibrations.
Once you have installed the first application of deadening material, take another drive with the radio on and find any leftover rattles.
Sound Deadening Materials
Road noise and engine noise are a completely different issue. CLD products do very little to stop radiated sound from entering a vehicle. This is where you will need to use a sound barrier product such as Mass Loaded Vinyl or MLV.
MLV products are made of a dense but flexible Vinyl that has a very low resonant frequency which makes it ideal as a sound barrier. When used properly this layer of MLV will encompass the entire vehicle from the window line down to create an environment that is isolated from the outside world. You need to make sure that you minimize any cracks or seams in this layer of MLV that would allow radiated sound to penetrate the cabin. This requires that you overlap the seams and use either tape or a vinyl adhesive to complete the seal.
Panel Vibration can be caused by the tires reacting to the surface of the road, the engine and drive train or even the sound system of the vehicle. The most effective way to eliminate this type of noise is to stop the vibration. The best way to do this is to add to the rigidity of the panel that is vibrating.
Constrained Layer Damper or CLD is the most common type of Sound Deadening that is used in Car Audio. CLD products are usually constructed with a layer of Butyl Rubber that is attached to a constraining layer such as Aluminum. CLD products are attached directly to the vehicle by a layer of adhesive on the Butyl Rubber side.
CLD products add mass to the panels of the vehicle in order to increase the rigidity of the panel which in turn stops the vibration. In most cases 50% coverage of a panel is enough to eliminate unwanted vibrations.
Road noise and engine noise can also be minimized by using a sound absorber. It can be very difficult to get MLV to adhere to an inverted surface such as the roof, hood or trunk of a car. The weight required to qualify MLV as a great sound barrier becomes a problem when trying to keep it from peeling away from the surface.
Closed Cell Foam or CCF is a good choice for these surfaces. Due to the size constraints of the vehicle CCF is not as effective as MLV at minimizing lower frequencies but it still does a good job at reducing higher frequencies. For any material to be effective as a sound absorber it needs to be 1/4th the thickness of the frequencies’ wavelength. Some sound absorbers have an added layer of protection from heat that makes them ideal for under the hood. They can also be used on the transmission tunnel and firewall to repel heat that is radiated by the engine and transmission.
The last type of noise is rattling that occurs when two or more vibrating panels make intermittent contact with each other. CCF can also be used as a vibration decoupler or cushion between two panels to stop the rattling. CCF is a great choice for this because the closed cell structure will not absorb moisture or odor from inside the door panel or liquids that may be spilled inside the vehicle.