Trunk Sound Deadening

How To Install Trunk Sound Deadening

How To Install Trunk Sound Deadening

We love cars of all shapes and sizes, and have a firm rule to never ever autobody-shame our fellow car enthusiasts. Real vehicles have curves, and we’ll be the first to admit we like a little junk in our car trunks.

But unfortunately, that junk can lead to sound distortion, rattling, and unwanted noise. Your trunk can not only let exhaust noise and tire noise leak in, but can also cause unwanted sounds from rattling, loose parts, and even your beloved subwoofer.

Luckily the trunk is one of the easier spaces to apply sound deadening and sound blocking material, think of it as Spanx for your car - keeping everything in place and absorbing all the vibration (maybe we should work on our analogies).

Soundproofing your trunk will go a long way to better car audio and a quieter cabin.

We love cars of all shapes and sizes, and have a firm rule to never ever autobody-shame our fellow car enthusiasts. Real vehicles have curves, and we’ll be the first to admit we like a little junk in our car trunks.

But unfortunately, that junk can lead to sound distortion, rattling, and unwanted noise. Your trunk can not only let exhaust noise and tire noise leak in, but can also cause unwanted sounds from rattling, loose parts, and even your beloved subwoofer.

Luckily the trunk is one of the easier spaces to apply sound deadening and sound blocking material, think of it as Spanx for your car - keeping everything in place and absorbing all the vibration (maybe we should work on our analogies).

Soundproofing your trunk will go a long way to better car audio and a quieter cabin.

Where's the Noise Coming From?

Much like your car door sound deadening project, the trunk is essentially an echo chamber made of metal panels with little or no insulation - we're talking some plastic paneling and thin carpet. Any flat or flimsy metal panel is going to vibrate and create structural noise. Look inside your trunk and what do you see? Big, flat quarter panels. A big sheet of metal as the trunk floor pan and covering the wheel wells. Top that off with a trunk lid that's often light, hollow, and not always firmly attached. You see a trunk. We see one of the loudest parts of your vehicle.

car noise pollution

Road Noise

Most car trunks sit almost directly above the exhaust and the rear wheels. Since there’s not much of a barrier, the low frequency road noise from these parts of your car easily leak into your trunk, where the sound bounces around and enters your cabin through the back seat and rear deck. This problem is amplified if you have a hatchback or have modified your exhaust or wheels.

Trunk Noise

Your trunk has a tough job. It houses your spare tire, a jack, roadside kits, tools, groceries, golf clubs, your gym bag, and whatever else you need to haul from A to B. All that rattling and daily cargo can cause quite the ruckus. And although a subwoofer is supposed to upgrade your car audio, your rear deck and trunk area aren’t built to handle that extra vibration (especially not the trunk lid). All of this combines to degrade the listening experience.

How to Soundproof Your Trunk

For a quiet trunk you have to stop the noise from coming in AND stop your trunk from creating noise. We offer several trunk insulation kits to make this as easy as possible. Each kit enables you to create two layers - the sound deadening layer, and the sound blocking layer. But before you add, you must take away...

STEP 1: Prepping Your Trunk

Before you get started, remove absolutely everything from your trunk and rear deck to get all the way down to the metal panels. This means taking out the spare tire, carpets, and trunk card (cardboard or carpet that covers the entire trunk floor pan). Carefully strip the walls of your trunk to expose the interior quarter panel and your trunk lid. The trunk lid is often forgotten, but it's one of the most important places to apply sound dampening material, especially if you have a subwoofer. Don't forget to consider the vibration that comes from your trunk lid bouncing and clashing with the closure as you drive along the highway.

If you run into wiring, do your best to safely tuck it into enclosures to keep it out of the way. If that doesn’t seem possible, decide whether you need to temporarily remove the wiring or if you would be able to work around it.

INSTALLATION TIPS

Thoroughly wipe down and clean the sheet metal with denatured alcohol. Damplifier Pro is very sticky on its own, but this will help your sound deadening material stick better.

STEP 2: The Sound Deadening Layer

You may be surprised to learn that most trunks are between 15 and 30 square feet. Ensure you have the right amount of butyl rubber sound deadening material for your space (never use asphalt!). Trunks are full of nooks and crannies so when dealing with tricky areas we recommend using a sharp utility knife to cut your deadening material down to smaller squares to make it easier to apply. Sound deadener is most effective if it’s fully adhered to your trunk, so apply firmly using a hand roller.

Try to cover at least 60% of the trunk, walls, rear deck, and lid with sound deadener. Focus coverage on the wheel wells as that’s the source of a lot of vibration. If you have a subwoofer, you should cover 100% of the trunk, including the lid. You also may want to use a decoupling foam, like OverKill Pro, to prevent the rear deck lid from rattling or bumping your back window. This is because your trunk is subject to much stronger vibrations then it would face from normal rattling and road noise.

INSTALLATION TIPS

If you decide not to cover 100% of the metal surface, put the bulk of the trunk sound deadener on the flatter, flimsier metal sheets. The curved parts of the trunk are more structurally sound and tend to rattle less.

If you're trying to conserve sound dampening material, use the checkerboard approach highlighted in Mark from CarAudioFabrication's video build.

STEP 3: The Sound Blocking Layer

Imagine unwanted noise is a thunderstorm. While sound deadening material only needs to go on some of the structure to keep your house from rattling, the only way to stay dry is to be fully covered from the rain. If you want to keep noise from raining on your parade, apply mass loaded vinyl to the entire floor and walls of your trunk. There are 2 approaches to this.

One of the easier methods is to adhere the material to the cardboard shelf or carpet that covers your spare tire. This gives you a template to know exactly how much material is required, and allows you to remove the material as needed. As long as the trunk is fully covered and the foam side faces down, you will get adequate sound blocking.

If you want to be thorough, the best way to keep out road noise is to apply sound blocking material directly over your sound deadening material. It’s imperative that you get FULL coverage, use foil tape to seal any gaps. External noise will leak through any opening it can find.

Note that most cars have a ‘relief vent’ in the trunk. This is a flap that equalizes the pressure when you close your trunk. DO NOT cover the vent! If you do, you may not be able to close your trunk anymore (physics is crazy).

Check out our Trunk Kits to get all the sound dampening material you need plus a hand roller and quality adhesive to fully soundproof your trunk space.

Our products are made of high-quality, fire-resistant materials with safety in mind. Our mats are 100% butyl rubber (no asphalt!) and are proudly manufactured in the US.

INSTALLATION TIPS

Be sure to check that your spare tire and other parts will fit back in their place with the addition of the sound blocking layer.

Next time you’re cruising along trying to enjoy your favorite song but can’t ignore the buzz caused by your subwoofer, the road noise from your tires, or that awful drone of your exhaust, remember the culprit - the trunk. Luckily with the right materials and a little time, you can get rid of that rattle and road noise, and all you’ll be left with is good vibrations.

Learn More with Our Ultimate Car Insulation Guide