Sound and vibration damping materials for the cabin

Acoustic panels and anti-vibration foams reduce road noise, wind noise and vibration transmitted into the cabin, noticeably improving the experience of vehicle occupants. For electric vehicles, this need is even greater because there is no engine noise to mask other sounds.

Cabin noise comes from three main sources: tires and the road surface, airflow around the body and vibration from mechanical assemblies. Each source has its own frequency range, so several types of material need to be combined rather than relying on a single solution.

Types of acoustic and anti-vibration materials

Bitumen or butyl damping sheets

Applied directly to floor panels, doors and wheel arches to reduce vibration of thin sheet metal. Clearly effective in the low frequency range below 500 Hz.

Sound-absorbing foam

Open-cell polyurethane foam or PET fiber absorbs mid and high frequency sound and is usually placed behind interior trim, in the headliner and in the trunk.

Anti-vibration cushioning foam

Closed-cell EPDM and PU foams are applied at contact points between plastic and metal parts to eliminate squeaks and rattles.

Key application areas

• Floor and wheel wells: reduce tire noise.
• Bulkhead between the cabin and the engine or electric motor compartment.
• Inner door panels: block outside noise and give a more solid door-closing feel.
• Headliner: reduce resonance at high speed.
• The gap between the dashboard and the windshield.

A piece of foam placed in the right spot can fix a noise that engineers have spent weeks tracking down. Anti-vibration is a game of small details. — AMS Automotive Application Engineer

Balancing weight and performance

Traditional acoustic materials are quite heavy and can add up to tens of kilograms per vehicle. The current trend is to use thinner damping sheets with a high loss factor, combined with lightweight sound-absorbing foam, placed only at locations identified through vibration analysis.

Evaluating effectiveness

The effectiveness of an acoustic solution should be measured with data rather than perception. Measuring the sound pressure level at the driver's ear position at 60 km/h and 100 km/h on the same stretch of road allows a before-and-after comparison of material changes. In the laboratory, the loss factor of damping sheets and the sound absorption coefficient of foams are measured using standard methods. An improvement of 2–3 dB in the cabin is already a difference users clearly notice.

Beyond passenger cars, similar solutions are also effective for electric buses, light trucks and construction machinery cabs, where operators work for many hours at a stretch.

For advice and samples of acoustic and anti-vibration materials for vehicles, please contact AMS Vietnam.