The Ultimate Sound Deadening Guide for Cars: How-To Install & What to Buy

The primary appeal of a brand new car is often attributed to the things that degrade the quickest. For appearance, these are usually high contrast pieces such as the headlights and external sun-exposed plastic. For sound, an often overlooked sense in this regard, it’s attributed to the isolation of inside noises and elimination of outside noises. As cars age, the grommets, seals, and jambs which filter out unwanted noise begin to weaken and wear. This leads to seeping road noise which increases the longer you own your vehicle. If applied correctly, however, sound deadening material can actually make your car sound new again. My sales pitch for Dynamat used to be, “you have no idea how much you want this until you already have it.” It’s basically the holy grail of vehicle acoustics. This post goes over everything you need to know about adding sound deadening to your car, focusing on my B7 Audi A4. Sound deadening serves three purposes; stop outside sounds from coming in, stop inside sounds from escaping, and reduce rattle and vibration both inside and out. The downside is that sound deadening material means adding weight; fifteen pounds for the doors alone, to be precise. If you’re the type who rips out back seats, spare tire, and door cards for race week, this isn’t for you. For casual racers who don’t care about their quarter mile time since the finish line is the grocery store, read on.

Which Sound Deadening Brand is Best?

When it comes to choosing a product, it becomes an equation of budget, surface area, and diminishing return. That is, how much are you willing to spend to squeeze out the last few fractions of a decibel from this application? If your budget is unlimited, go with Dynamat. It is indisputably the best, to the extent that this application is most commonly referred to as Dynamatting your car. Indeed, sound deadening is to Dynamat as copying papers was to Xerox. My budget is not unlimited, however, so I bought Noico sheets. My thinking was that I would rather spend the same amount of money and cover double the surface area, as I believe that will have a much higher yield than less surface area of the better product. The phrase “a little Dynamat goes a long way” may hold true, but I submit that “a lot of Noico will go further.”

Where to Place Sound Deadening/Dynamat?

Sound deadening material is often mistakenly thought of as a shield from outside noises. It should more accurately be thought of as a sound absorber, affixing itself the surface to reduce the surface’s ability to vibrate. Imagine an empty can sitting on a table. Now imagine flicking it with your finger and the tonnnng it makes afterward. Now imagine holding that can firmly in your hand and giving it the same flick. Where before it resonated and rang, now it merely gives out a short tink. This same principle is applied to sound deadening your vehicle. The sheet of carbon steel that forms the outermost body of your door acts exactly the same as an empty can. Thick tar, supported by aluminum, which together make up the sound deadening material, act the same way your hand does around that empty can. Instead of trying to cover up all the spaces in an attempt to block out the noise, try to find spaces in your door’s body and frame where you can turn tonnnngs into tinks. Literally, if you tap a piece of metal and you hear a low pitch ringing, apply material to or around it. Most luxury vehicles already offer a light dressing of rubber on the door body to absorb road noise, but this too degrades over time, hardening with the hot and cold cycles until it has completely set. If your vehicle is over five years old, it has seen thousands of hot and cold cycles, so it’s probably safe to assume your factory sound absorber has cured and is therefore less effective if not altogether useless.

In this DIY we’ll focus on the doors, but if you have an open car (i.e. hatchback, station wagon, SUV) or other side panels those are worth doing too.

DIY / How to Install Sound Deadening (Dynamat):

Difficulty: 3/10
Estimated time to completion: 5 hours, regardless of experience.

Tools needed to install:

• A sound deadener roller
• Tennis ball
• Replacement door clips
• Hand pruning shears or long bladed snips
• Auto body repair tape
• 3M yellow weatherstrip adhesive (no substitutions)
• Panel popper kit
• Phillips head screwdriver
• Torx screwdrivers size 6 and 8
• A cleaning solution, like rubbing alcohol, and several clean rags
• Sound deadening material such as Dynamat, Noico, or FatMat

The first step is to remove your door cards:

After this, remove the speaker housing completely. Then unscrew the control unit (three screws – top, side, bottom) and gently let it hang. Now carefully remove the metal tape strip at the top of the foam liner, then the foam liner itself. We will be reapplying the foam piece, so try not to damage it too much. Peel off the string of factory sealant. At the end of this step, all four doors should be bare metal. Note: On titanium trims and perhaps some others, there will be one or two cubby-shaped plastic pieces. The purpose of these is to provide an air-tight seal, however, as you can see, they have likely hardened and are not serving much of a purpose anymore. If you have them, remove them. We will be replacing them with a much stronger material.

The next step is to clean inside your doors thoroughly with a cleaning solvent. The tar from the Dynamat will need a clean surface underneath it to ensure a tight seal. Check the images below to see where you will be applying your sound deadening material.

We will focus on the door body (the flat part behind the frame) first, since that is the first line of defense against road noise. Begin by laying out your dynamat and cutting it in such a way as to cover the most surface area possible (red dashed line). Once this is complete, chop it up into smaller pieces which fit more easily through the holes in the door frame (pink dashed line).

After those pieces are cut out, apply them to the inside panel and vigorously press the roller into the material. Many sound deadeners have ridges which let you know you’re done rolling when the ridges flatten out. Here is an example of that application:

and this is what your door should look like when you’re finished:

After you’ve dynamatted all four door bodies, turn your attention to the frame. Tap your knuckles against the metal to find spots that tonnng and again begin aggressively applying material to these places, using the same technique as seen in the video above. Where you find rounded edges inside which the rolling tool is not sufficient, use a tennis ball. Here’s a heatmap of where I found the most ringing:

The final step is to permanently plug the holes in the door frame. Something to consider about this step is that anyone who has to repair the window, track, or wire loom in the future will have to cut through this sheet of dynamat. Here are the 2-3 holes we’ll be plugging. Green is recommended, blue is optional.

An optional step at this point is to cut out the corresponding concaves of the black foam door insert we removed earlier, as the holes in which those concaves used to rest are being closed up. In order to give the material a surface to adhere to, begin placing overlapping strips of automotive repair tape inside the holes.

Then, cut and apply your sound deadening material overtop. Be careful to avoid trapping air between the tape and the tar. Repeat this process on all the holes you wish to plug.

Finally, in preparation for reassembly, draw a line along the track of the foam door insert and let it rest until it is tacky.

Then, remembering to slip the handle hook through the hole, reapply it to the door frame. Then screw in the speakers and control units.

Replace any door clips damaged during removal, and reinstall the door cards and trim pieces, then you’re all set!