How effective is the sound insulation in a car trunk?
4 Answers
Trunk sound insulation is effective. Installing sound insulation cotton in the trunk can absorb some of the energy produced by noise and convert it into heat for dissipation. Applying soundproofing and vibration-damping panels to the trunk can effectively reduce vibrations during driving, while adding sound-absorbing cotton on the outer layer can effectively block exhaust pipe noise as well as tire and road noise during driving. Additionally, performing the same sound insulation treatment on the wheel arches inside the trunk can further prevent tire noise from entering the cabin. The sound insulation materials used should meet the following standards as much as possible: 1. The material should be lightweight, as lightweight is a major trend in the automotive manufacturing industry. Lightweight materials won't significantly increase the vehicle's weight or fuel consumption after installation. 2. It should have good sound insulation and absorption performance across a wide frequency range, with long-term stability and reliability. 3. It should have sufficient strength, be resistant to damage during installation and use, and have good aging resistance, weather resistance, and a long service life. 4. It should have a clean appearance and be pollution-free. 5. It should be moisture-proof, waterproof, corrosion-resistant, insect-proof, and resistant to mold. 6. It should be non-flammable, preferably fire-retardant. 7. It should be an eco-friendly material, free from harmful substances such as asbestos or fiberglass. 8. The material itself should be easy to work with, such as being easy to cut and firmly adhesive.
After driving so many cars, I've found that trunk noise insulation mainly depends on two things: the material of the floor panel and the wheel arch treatment. Last time when I helped a friend deal with the noise in his old Accord's trunk, we took it apart and saw that the factory only had a thin layer of felt, with no sound insulation material on the inner side of the wheel arches at all. The sound of pebbles hitting the tires directly transmitted into the cabin. After DIY installation of damping sheets + sound-absorbing cotton, the tire noise on the highway was reduced by at least 30%. But be careful not to block the drainage holes—once I saw a modification shop forget to leave drainage channels, and when it rained, water accumulated in the spare tire well in the trunk.
As a father of two who frequently takes road trips with kids, trunk quietness is absolutely crucial. I noticed a detail when loading the stroller: hatchbacks are half a notch worse at noise insulation compared to sedans. Last time I rented a Volvo V60, when closing the tailgate after installing the child seat, there was a satisfying airtight 'whoosh' sound. But when doing the same in my cousin's Camry, noticeable wind noise from the trunk became apparent above 60 km/h. My engineer friend explained sedans have extra insulation barriers between the rear windshield and trunk. Now when car shopping, I always knock on the trunk lining - only a dull thud sound gives me peace of mind.
Back when I was into car audio modifications, I specialized in trunk acoustics. The most effective approach was a double-layer treatment: first applying vibration damping sheets to suppress steel panel resonance, then laying soundproofing cotton to absorb mid-to-high frequencies. I remember being lazy during my first Honda Fit modification and only using cotton - the subwoofer still caused annoying vibrations. Later I discovered the spare tire well is an acoustic trouble spot, so now I always fill cavities with expanding foam. However, full soundproofing adds 19kg (38lbs) and increases fuel consumption by 0.2L/100km - you really can't have your cake and eat it too.
