From the hum of a car’s engine to the squeal of tires on asphalt, sound affects your driving experience as much as smooth handling or a comfortable seat. When automotive manufacturers design cars, trucks and other vehicles, they listen closely to pinpoint sources of unwanted noise both inside and outside of the cabin.
Automakers rely on noise, vibration and harshness (NVH) engineering to study and control those different types of sounds. They use a combination of NVH treatments to give drivers and passengers a quieter ride and protect components, such as the transmission and joints, from damage and premature wear.
More traditional NVH approaches are often unwieldy and time-consuming to install, requiring the use of heavy pads or foams.
Newer technologies — called liquid-applied sound damping (LASD) and liquid-applied sound barrier (LASB) systems — use spray application to help automakers dramatically reduce weight, labor and material costs.
Noise reduction in vehicles: NVH 101
Whether it’s wind whistling against car doors or vibrations from electrical actuators, noise comes from several different parts of the vehicle. Some are structure-borne noises generated by vibration, while others are airborne sounds that reflect off surfaces.
NVH materials can be categorized in three ways: vibration damping, which isolates structural noise; barrier treatment to block the transmission of airborne noise; and sound absorption for airborne noise.
Among the three types of NVH materials, there is some overlap with the usage of LASD and LASB solutions. Here’s a breakdown:
- LASD is used primarily in vibration damping and occasionally in barrier treatment.
- LASB is used primarily in barrier treatment and occasionally in sound absorption.
“Structural noise is low-frequency — between 0 to 1,000 Hz,” says Akbar Hussaini, technical specialist for LASD and NVH coatings at BASF. “That’s where LASD is used. As you go higher in frequency scale towards airborne noise, that’s where more flexible coatings need to be used. As a flexible, water-based coating, LASB is used to create a barrier in these cases.”
In other words, LASD and LASB systems are used in different parts of the vehicle to treat different sources of noise. They are both poised to take over traditional NVH materials by offering significant cost savings.
LASD: Liquid-applied sound damping
Uses: Vibration damping for structural noise
Applies to: Metal surfaces
Traditional method: Die cut pads (asphalt or butyl)
Liquid-applied sound damping (LASD) technology mainly addresses structural noise. While its primary application is in the automotive industry, it is also used in appliances such as sinks, dishwashers and large-panel surfaces.
Vibration damping traditionally requires the installation of asphaltic or butyl die cut pads on the bottom of a vehicle. These large, heavy sound pads can be quite labor-intensive to install, requiring the help of multiple workers.
“In the past, you needed one person per door opening to install sound damping pads,” says Hussaini. “You might have two to six people per shift, over three shifts, installing them.
The pads also require significant storage space. In response to those demanding installation requirements, LASD was designed for a comparatively fast and simple application process.
By replacing the pads with one LASD coating, we reduce part inventory, part complexity and injuries.
Akbar Hussaini
Technical Specialist for LASD and NVH Coatings
“LASD is a sprayable, robotic application,” Hussaini explains. The coating is sprayed in patches on the bottom of a car’s floor pan, suppressing vibrations in the vehicle’s body or chassis.
BASF recently helped Cadillac develop a LASD coating with its Acronal® 4053 X and Acronal® NX 4569 products. The result was an effective sound damping system that can be applied in mere minutes — a far cry from the time-consuming and difficult die cut pads.
LASB: Liquid-applied sound barrier
Uses: Barrier treatment for airborne noise
Applies to: Nonmetal surfaces (e.g. PET/shoddy fiber)
Traditional methods: Plastisol coatings, PU shields, foams
In addition to LASD systems, automakers are beginning to use newer liquid-applied sound barrier (LASB) technologies to address issues of airborne noise.
A recent project had BASF involved in the creation of a new DashMat made from a length of shoddy fiber covered with a film of LASB. The base resin is called Acronal® NCR 8001.
“The DashMat is about 25 square feet. It’s the largest NVH piece in the vehicle,” says Hussaini. “It’s installed behind the instrument panel as a barrier treatment for airborne noise.”
In the past, automakers used PET, foam or shoddy fiber backed by EVA as the barrier layer. As the industry focused more on reducing weight in the vehicle, they ran into limitations with the thicker, heavier EVA layer.
“The EVA laminate wouldn’t go thinner than a thousand grams per square meter, and that’s where it would tear,” Hussaini explains. The fix was to remove the EVA layer and add a sprayable coating, or LASB, to do the same job. “The LASB spray actually lets you realize all the way down to 250 grams per square meter and still be continuous.”
Driving changes in NVH reduction
In the case of LASD coatings, the job of installing die cut pads poses several problems for employees. For one, lifting the heavy pads carries a greater risk of injury. When workers open boxes of pads, they also tend to release debris that hangs in the air and infiltrates the vehicles.
System flexibility is a big advantage of LASD and LASB coatings.
As a result of those factors, Hussaini says the job comes with a higher rate of absenteeism. “By replacing the pads with one LASD coating, we reduce part inventory, part complexity and injuries.”
That’s in addition to the overall savings in time, labor and material costs proffered by LASD and LASB systems. The coatings are formulated for lower VOC output, allowing manufacturers to keep their processes green with fewer hazardous air pollutants.
“System flexibility is also a big advantage,” Hussaini adds. If manufacturers need additional noise control in a certain area of the vehicle, they generally need to design a new mold or die to create another pad — a process that costs tens of thousands of dollars. “With sprayable coatings, all they have to do is reprogram the robotic applicator to spray more material in the designated area. They can have it done in less than an hour.”
Both types of coatings have already been used to optimize weight and soundproofing in projects with prominent automakers. BASF plans to roll out its new LASB product offerings in the near future.