Keeping It Quiet for Reproducing Great Audio

The car is a noisy environment for reproducing great audio. Between road noise generated by tires spinning on the pavement, wind noise caused by the vehicle cutting through the air at highway speeds, and engine noise constantly droning away, it can be difficult to enjoy a car audio system while driving down the road at the speed limit.

You may have noticed that some cars are quieter than others. The interior of a Cadillac, for example, is much quieter than that of a Chevy Lumina. That’s because carmakers use more sound-deadening material in luxury cars to keep exterior noise at bay, and much less in economy vehicles.

Sound-deadening material

Because noise can rob a system of good sound, car audio enthusiasts add sound-deadening material to their vehicles to get the same sort of quiet ride found in luxury vehicles, sound-deadening material generally comes in self-adhesive sheets that can be applied to the metal parts of a car (see Figure 19-3). It’s also available in a liquid form that can be sprayed on, although application of the liquid requires a power sprayer and is best left to professionals. You can buy sound-deadening material from a car audio retailer or order it online.

Sound deadening works by adding mass or weight to an object; in this case, the metal panels of a car. Every object has a resonant frequency (the natural frequency at which it vibrates), and those vibrations cause noise. A car creates plenty of vibrations: from the engine, from wind, from the road, and even from speakers in a car audio system. Adding mass to an object lowers its resonance frequency, and more energy is required to make it vibrate. It’s like when, say, a table is vibrating: When you put your hand on it, it stops vibrating and stops making noise.

Of course, adding more weight also makes the vehicle heavier, which can lower fuel economy. If you’re only using sound-deadening in, say, your doors, this may not be a big issue, but if you’re adding it to your whole car — and you racQ in sanctioned events on the weekend — it could be. 

Figure 19-3:

Scosche

Accumat

sound-

deadening

material. 

Courtesy of Scosche

Besides stopping unwanted resonances, sound-deadening material also helps form a barrier that road noise and wind noise have a harder time penetrating. And it can block heat from the engine compartment. These are two reasons it’s used by hot rod and custom-car builders.

Adding Sound-deadening material is a modification that a DlYer can easily tackle. For detailed tips on how to do it, see the “Installation Tips for Accessories,” section later in this chapter. Sound-deadening material can be applied almost anywhere in a vehicle, such as on the

Doors (Figure 19-4)

Floorboard (Figure 19-5)

Roof (Figure 19-6)

Trunk (Figure 19-7) 

Figure 19-4:

Dynamat sound- deadening on a door.

Courtesy of Dynamic Control

Figure 19-5:

Dynamat sound- deadening on a floorboard.

Figure 19-6:

Dynamat sound- deadening on a roof.

Courtesy of Dynamic Control

Figure 19-7:

Dynamat sound- deadening in a trunk.

If you want to add sound-deadening to your car, start by covering the area you can most easily reach, such as the inside of the front doors. (Manufacturers of sound-deadening material even offer kits specifically for doors.) See what sort of effect this has. If it resolves the problem, you’re done; otherwise, move on to harder to reach areas. In extensive car audio systems, installers will sometimes start by completely stripping the interior of a vehicle and covering every metal part of the interior with sound-deadening material to ensure a quiet environment.