Car Audio - Trunk Rattle

The Woes Of Trunk Rattle
by Dave Sumner

700 watts of audio power plus 4000 lbs of road-worthy ride, and your set for cruising the strip on Friday night, right? You throw in your favorite CD and hit the road, ready to impress. The only flaw in the plan, is there is more trunk rattle than music. People on the strip are pointing and laughing at you, and you can’t get back to the crib fast enough.

Its okay my fellow audiophiles, this kind of thing happens to the best of us. So how do we fix it? Its all in the system design. Its not a quick fix, but you’ll be back on the strip Saturday impressing the locals.

Trunk rattle happens because the air pressure from the subwoofers is not directed towards the passenger area in a vehicle. Some will tell you that sound is not directional, and to this they are correct. However, air pressure is directional and is the number one cause of trunk rattle. If you light a candle and blow out the flame, the smoke rises straight up. If you blow out the flame and place your hand two inches above the candle, the smoke spreads out around the hand in several directions. The "boom" from the subs is doing the same thing. You put your subs in a box in the trunk facing out so you can impress the crew when you pop the trunk lid. This is the main cause of trunk rattle. Face the subs towards the back seat instead. This pushes the air pressure towards the passenger compartment - directing more sound and bass towards you, and saving the trunk lid from suffering the blunt of it. 

"But Dave," you say, "What if I’m pumping a 15" Fosgate and I only have 12" of height in the trunk?" Fear not my future hearing-aid customer, angle the box so the sub doesn’t face the trunk lid directly, and if you can, make the ports in the box face the back seat. You are relieving the air pressure as much as you can, while it is being re-directed.

If you simply don’t want to do this, there are some "backyard fixes" that can help. Sound-dampening material can be applied to the trunk lid and rear deck, then covered with carpet or upholstery. This will absorb the sound and air pressure, but not prevent it. I would also recommend installing rubber washers with the bolts that attach the trunk lid.

Lastly, a small tip for all of us: Take a small piece of Velcro and affix the softer side to the back of the license plate. You can place the other side on the car’s body if you want, but it isn’t necessary. This will keep the license plate from rattling against the car’s body with the bass kicked up.


Dave Sumner 
XSNoise Car Audio