When making a vehicle quieter you have three fundamental ways of stopping the unwanted noise reaching the cabin and your ears:
1 – Stop Vibration
Noise from the vehicles engine, tyres and general road noise can make the metal panels vibrate. These vibrations are amplified by the resonating panels essentially turning your vehicle into a giant speaker. By applying a sound deadening mat to the metalwork the vibrations will be damped and the vehicle will seem instantly quieter.
2 – Absorb Sound
Once you have killed the vibrations you need to deal with the airborne noise that is still coming through the doors and floor etc. It is only practical in a vehicle to absorb the higher frequencies therefore a range of foam products are available to apply on top of your damping mats and to fill hollow voids eg roof void etc. (These foams are also excellent at isolating trim panels that may rattle or squeak)
3 – Block Noise
Low frequency road and exhaust noise cannot effectively be completely absorbed in a vehicle as the thickness of foam required would be impractical. It is therefore required to block the incoming noise with an effective barrier. The best solution in a vehicle is to use a heavy vinyl layer (MLV). Ideally this should also be isolated from the panels using a foam decoupling layer.
Conclusion
The ultimate solution for a vehicle is therefore to reduce panel vibrations with sound deadening mat, add a layer of foam absorber and finally a layer of mass loaded vinyl to block the sound.
Obviously all these layers may not be practical for all users and installations, however with these rules in mind you should be able to plan the best solution for your needs.
