How to Muffle Your Car Trunk for Subwoofers

Subwoofers can exert pressure blasts that can produce harsh low-frequency vibrations.

A lot of vehicle owners who have installed subwoofers in their trunks have discovered that along with the bass frequencies comes an annoying rattle or vibration. Sometimes a discernible amount of volume escapes from the trunk to the outside, which can annoy neighbors and result in sound equipment violations. Metal material has a sound resonating frequency, and when exposed to low frequency pressure waves, amplified sound becomes trapped and interacts with the surrounding metal. A vehicle owner has a few options and tricks to muffle his trunk for subwoofers, which can provide a cleaner bass frequency flow, allow less volume and produce better acoustic listening pleasure.

Things You'll Need

• Putty knife
• Dish washing soap
• Bucket
• Scrub brush
• Towels
• Socket set
• Ratchet wrench
• Screwdrivers
• Tape measure
• Acoustic dampening material
• Roller
• Razor knife
• Spray or tube silicone adhesive

Instructions

1. Place your vehicle in park or neutral, depending upon your transmission type, and set the emergency brake. Open the trunk. Remove any loose or semi-permanent items such as the spare tire, jack and tire iron, subwoofer boxes and spare tools. For carpeted trunks, including floors and seat panel walls, lift up on the securing snaps or prongs and peel the carpet back. Some models may have Velcro, or screw-down brackets. If the carpet has gum adhesive, pry under it with a large blade putty knife and gently pull it away from the metal. Remove any foam pad, if so equipped, in the same manner.

2. Pull the trunk drain plug, or spare tire wheel well plug, out of its stopper hole. Use a hose to wet the trunk, spraying the heaviest debris down the drain hole. Mix some dish washing soap in a bucket, then clean the trunk floor, wheel well, quarter panel walls, rear wall and rear seat deck wall. Rinse thoroughly and dry with absorbent cloth towels. Replace the drain plug.

3. Look on the inside of the trunk for any bolts or screws such as the underside trunk mounting bolts, spring and fulcrum bolts (for those models), interior license plates nuts or screws, trunk lock mounts, taillight mounting screws or nuts and any frame or bracing nuts or screws. Use a socket or screwdriver to tighten them. For vehicles that have fuel filler necks entering the trunk space, make sure they are stable and not riding against the quarter panel, causing any vibration. Look for emission control and gas tank vent hose brackets; tighten the brackets with a socket or screwdriver.

4. Measure the trunk width and length with a tape measure, and multiply one number against the other to arrive at your total square feet; be sure to include the wheel well. Purchase enough acoustic dampening material to cover your trunk area. The peel-and-stick variety dampener saves times and cost and is made by several manufacturers. Typical stick and peel dampeners come in 12.5- by 30-inch sheets.

5. Lay your straight sections of peel-and-stick dampener first, until you reach the seam margins. Use a roller to press it down from end to end. Use a razor knife to cut away access at the seam joints. For tight curves, such as those in deep wheel wells, cut thinner strips of stick and peel, and conform it to the curves by hand, then firmly roll it.

6. Cover all sides of the trunk panels, but leave room for any bracket attachments (spare tire), and leave taillight housing brackets uncovered. Do not forget the underside of the trunk lid -- simply roll the peel-and-stick over the trunk lid bracing and trim it to size.

7. Lay beads of silicone down over the peel-and-stick dampener material. Look at the underside of your carpet or foam padding, to gauge how much to use and where to place it. Replace your carpet foam pads with silicone, if you have this type of configuration, then lay additional beads of silicone on top of the foam pad. Replace your carpet sections, aligning them with the pattern profile and the snaps, Velcro hooks or screw-down brackets. Use a screwdriver to secure the screw-down brackets, if equipped.

8. Use your hands and roller to go over the carpet, pressing firmly along all the seams and curves. Make final trim cuts with the razor knife, if any peel-and-stick material protrudes outside of the carpet. Reinstall your spare tire, jack and tire iron in the trunk, if equipped. Place the subwoofers back in the trunk, mounting them to their brackets or supports. Reconnect the subwoofer wires. Test your sound system with the trunk closed, noting the difference before and after.

Tips & Warnings

• Some trunk insulating kits come with gasket, or insulating foam material. This material is sponge-like and is used to brace the under side of hard fuel lines and hoses so they will not chaff the metal. Gasket foam is applied by cutting it to size and sticking in place.

• Check the weather-stripping gasket between the trunk lid and frame. If it is deteriorated, worn or crushed flat, purchase a new length of it from a hardware or auto supply store. Use silicone adhesive to mount it in the frame joint.

• For vehicles that have spring pressure hold-down snaps that hold the wheel-well cover in place, adjust the spring rods by bending the metal so the hold-down tension increases.

References

• Dynamat: Dynaliner 1.0
• Cheap Car Stereos: How to Avoid "Trunk Bass"
• Cascade Audio Engineering: Universal Trunk Kit