Acoustic glazing consists of two or more sheets of glass, bonded together with one or more acoustic interlayers. The interlayers act as a noise-dampening core, weakening the sound as it travels through the glass. Acoustic laminated glass also benefits from all the safety and security properties of standard laminated glass. Moreover, acoustic windscreens reduce the need for heavier glazing, which allows car manufacturers to reduce vehicle weight.
*This will not affect commercial trucks where the need is more in mitigating the damage from stone impingement than noise. This is achieved by using an asymmetrical windshield.
Reducing the noise level of a vehicle cabin is an important factor for passenger comfort. It is also important for safety concerns because noise is believed to reduce driver efficiency over time. Sound transmission loss through a glazing system can be induced by mass, stiffness, and damping. Sound Transmission Loss (STL) represents the amount of sound, in decibels (dB), that is isolated by a material or partition in a particular octave or 1/3 octave frequency band. In reality, there is a limit for increasing the mass, or the thickness of glass, and also for controlling stiffness due to the limit of glass design. To increase damping effectively and obtain good sound attenuation, laminated glass is used with a viscoelastic plastic interlayer that changes vibration energy into heat energy.
The human ear can hear sounds in the frequency range from 20 Hz to 20,000 Hz, and it is especially sensitive to sounds in the range of 1,000 Hz to 4,000 Hz. In case of a 4mm thick single glass plate, the frequency range for its coincidence dip is around 3,000 Hz. Wind noise comes from air blowing across the car body and is transmitted through glass parts, which then increase the interior noise level. This noise mainly includes high frequency sounds around 1,000 Hz to 5,000 Hz. Multi-layer acoustic PVB interlayer shows the highest STL value over monolayer acoustic PVB and normal PVB interlayer, especially in the coincidence dip range of 1,000 to 4,000 Hz. Therefore, high frequency sounds like wind noise from outside is effectively blocked by a multi-layer acoustic PVB interlayer. Special acoustic PVB interlayer, acoustic film has been adopted by several automobile manufacturers not only for high-end luxury vehicles but also for mid-class passenger cars. It achieves a quieter interior. Because of these acoustic properties, the manufactures can reduce the weight of the vehicle by using thinner (normally acoustically inferior) glass, which in turn results in better fuel efficiency.