Closing the door on cabin noise

Trends and drivers

Acoustic glazing is part of mainstay technology for noise, vibration, and harshness (NVH) engineers to improve cabin sound quality and create a premium cabin experience. More than 50 percent of globally-built vehicles already have an acoustic PVB interlayer in the windshield, and the outlook for this trend continues to rise.

Now there is an even faster growing segment for including acoustic glazing in the vehicle door glass, or side laminate position. It is estimated that 10 to 15 percent of vehicles built globally come with acoustic glazing in—at minimum—the front side glass. This trend is expected to grow by more than 10 percent annually.

Three factors are driving the adoption of acoustic side glass at the manufacturers’ level:

  • Growing demand for the inclusion of voice-control features, which require a quieter cabin to enable optimal voice recognition
  • Vehicle size. Approximately half of all OEM builds globally are either SUVs or pickup trucks. These vehicles tend to have larger A-pillar and sideview mirror designs that create significant wind turbulence at higher speeds.
  • Fuel economy. Internal combustion engine (ICE) vehicles have more stringent fuel economy standards to meet, and there is growing demand for electric vehicles (EV) with better extended driving ranges. Lighterweight materials are a necessity to achieve better fuel economy, no matter what type of vehicle.

 

An uptick in voice-activated technology

Adoption of smartphone connectivity technologies within vehicles has grown dramatically in recent years, from 40 percent of global OEM builds offering smartphone integration in 2015 to more than 65 percent in 2020. Premium OEM brands were the first to adopt this technology, but it has since become a standard feature on trim levels of many mass market vehicles. Because of this growth of voice-interaction technologies, the need for a quieter and more balanced cabin acoustic environment is required to ensure function of device microphones. Acoustic glazing is a key component of how OEMs look to create the ideal environment for voice interaction, particularly in addressing wind noise and rain noise.
 

 

Larger vehicles equal more noise

The popularity of larger vehicles such as SUVs and pickup trucks means that NVH engineers must take greater care in damping down noise levels in the cabins. Because wind turbulence at higher speeds grows louder due to the design of the larger A-pillar and sideview mirrors, SUVs and pickup trucks can benefit greatly from side glass acoustics.

 

The lighter side of acoustic side glass

OEMs use acoustic glazing in vehicle door glass for improved cabin acoustics, but there is another benefit or bonus. Laminated acoustic side glass provides vehicle weight reduction for improved fuel economy in ICE vehicles and extended driving range in EVs compared to tempered glass.

Most vehicles today without laminated side glass have either 4-mm or 5-mm tempered glass. A typical set of approximately one square meter area will weigh between 10 kg and 12.5 kg. By using an acoustic PVB interlayer set between two panes of 2.1-mm glass, the total weight for the same one square meter area of acoustic laminated side glass would weigh 11.3 kg.

The payoff? The OEM can achieve a significant increase in acoustic performance while maintaining a similar weight as industry standard tempered glass.

New innovations in side laminate construction could improve this further through the use of thinner and more asymmetric glass constructions. Thin, symmetric constructions of 1.8-mm glass are starting to gain adoption. In this configuration, the side laminate pair would weigh about 9.8 kg and would still offer significantly better acoustic performance than tempered glass. Asymmetric glass constructions will help provide additional stiffness to the laminate by shifting the center of mass toward the thicker, outer pane. This works particularly well in frameless or flush-mounted door designs, which are popular among EV and performance vehicle manufacturers. In this scenario, OEMs can achieve enhanced design and acoustic performance at similar or reduced weight versus traditional tempered glass.

 

What side glass acoustic glazing provides

Since vehicle windshield designs and installation angles are more attuned to aerodynamics and the turbulence created by wind, they have become less of a contributing factor toward noise penetration into the vehicle cabin. Moving on to the side glass in doors is the next logical place to reduce cabin noise.

Side glass makes a significant contribution to cabin noise. Vehicle A-pillars and sideview mirrors create areas of turbulence and pressure fluctuations as air flows around them. This causes the side glass to deflect and bend, creating vibrations that are transmitted into the interior of the cabin. Side glass is also a transmission path for passing traffic noise from other vehicles.

Acoustic simulations and wind tunnel testing indicate that front side glass is actually a much higher contributor to cabin noise than the windshield. In one simulation where a vehicle was modeled both with and without acoustic PVB in the side glass, interior cabin noise was five to eight dB lower in the 3,000 to 5,000 Hz range in the vehicle with acoustic glazing in both side and windshield positions, versus acoustic glazing in the windshield alone (see comparison graphs).


Source: SAE article (2012); fft

 

 

Windshield laminated, side glass tempered:

Windshield + side glass laminated:

With innovations to vehicle door glass using acoustic PVB, OEMs can close the door for good on interior cabin noise.

 

Find out what Eastman has been doing to improve its Saflex automotive acoustic interlayers.