
A Guide to Car Sound Deadening
Strip down any big-brand luxury vehicle, and you’ll find among other things piles of sound-deadening products under that plush carpet. There’s a reason why cars verging on bigger sizes and at the higher end of the pricing scale are whisper quiet inside. They have more than a few layers to drone out sounds and vibrations emanating from different areas. Tyre, road and wind noise all need to be silenced. As well as the excessive engine, transmission, and exhaust bangs, pops, and rumbles. These can get to irritating levels in older and cheaper cars that are missing out.
Car makers need to meet fixed price brackets, and cost-cutting (when treating excessive noise) is one way to get that done. While all brands are now focussing more attention and effort on noise, vibration and harshness (NVH) levels with better sound deadening in newer model versions, drivers of all vehicles can always go the aftermarket route. A range of different products is used in different areas in vehicles and combined to the best effect.
Contents
What Sound Deadening Encompasses
Sound deadening and dampening are two notions used interchangeably, though ones that involve different stages of soundproofing your car. Deadening is done first. In the broadest sense, it means isolating areas and car parts that vibrate, often to the point that they create resonance causing other parts to do the same. The resulting noise gets louder as speeds increase. The main culprits in this sense are the vehicle floors. Vibrations and noise created here need to be isolated from the rest of the car before matters get out of hand. This is often done with a car floor sound deadening butyl layer.

Any stronger vibrations are absorbed or dampened with additional materials that lend mass. This is the second stage, where mass noise liners are used. It implies that stubborn sounds and noises are decoupled from the rest of the vehicle, or in simple terms, excessive sounds are droned out.
Materials in Sound Deadening and Dampening
Older cars have tar or bitumen-based sound-deadening materials, that will decompose into a crumpling mess over time. It will also start to smell. Removing this may be the hardest part of any soundproofing project. New materials comprising of thin butyl rubber noise absorption sheets, with a top aluminium layer can fit into all vehicle spaces and crevices, easily moulding to uneven contours and surfaces. It also sticks well, with the adhesive bottom layer. The combination of materials not only stops sound in its tracks but has the added benefits of being waterproof and highly heat resistant. This prevents rust pockets from forming and excessive radiant heat from engines and transmissions from seeping into the cabin.
Anyone intent on hearing the finer nuances of their favourite songs knows that this level of soundproofing is not enough. An additional acoustic layer that is also thicker (from 4 to 12mm depending on the vehicle) is what is needed to absorb the remaining sound. This is composed of a twin layer, open and closed-cell foam and is often lined with adhesive. The same car floor sound-deadening combination is used to line the front and rear firewalls and the wheel arches.
An alternative (and similar) solution that goes on top of the initial butyl rubber layer is a mass vinyl liner. This adds weight. It consists of a thinner mass-loaded upper vinyl layer with a 10-12mm thick closed-cell structure to deaden what’s left of noises that have permeated the butyl rubber. The material is an ideal option for carpet underlay, as besides sound deadening it is also highly effective in keeping heat and liquids at bay. Both car floor sound deadening products are durable and won’t rot. In addition, lining the floor is straightforward with either material. They’re cut to size with simple household scissors or knives. Mass vinyl has the advantage in that it can be easily removed, for instance in thorough car detailing.
While these are the materials reserved for car floor sound deadening, insulating and soundproofing other areas are also as important. Doors for instance are first lined with a butyl sound deadener. And on top of this goes a thicker closed-cell foam, applied with a vehicle-grade spray adhesive. An additional layer of sealant tape can separate this from the factory door trims. The same two-stage soundproofing, with the same materials, is used to deaden and dampen sound in the roof, quarter panels, walls and boot floors.
What You Get When Soundproofing Your Vehicle?
In floors, firewalls and arches, soundproofing materials will considerably reduce road and engine noise. Separate under-bonnet insulation, resistant to high heat, provides a helping hand in overall noise and heat reduction. This is further improved by installing insulation in the quarter panels and boot floor. Adding lining to the doors drones out wind and tyre noise and any rattling in side panels.
The results can be verified with a decibel meter. In-cabin noise levels are measured with the engine idling, and also at highway speeds.

Who Will Benefit the Most from Sound Deadening?
Anyone rebuilding an oldtimer or resto-modding a classic will see considerable advantages with the various sound-deadening products on offer. The absence of rattling and resonating vibrations is worth the effort alone. Besides this, heat is brought to a tolerable level, and floor pans are kept clean, and free of liquids and odours.
The products are also widely used by 4×4, ute and van owners. Stock sound-proofing here is mediocre at most and additional materials can prove their worth on unsealed roads, when off-roading, or at the worksite. At the end of the day, even regular hatchbacks and SUVs or any car with a bit more mileage will see sound improvements.
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