Use of compliant adhesive layers in direct glazing of road vehicles for improved sound attenuation

Abstract Particularly at low speeds and on poor road surfaces, the noise level inside a moving vehicle is determined to a significant degree by tyre noise in the low-frequency range (up to 500 Hz). Vibrations transmitted from the tyres to the window glass via sound bridges produce pressure oscillations inside the passenger compartment which are perceived by the vehicle occupants as noise. Finite element calculations, which are confirmed by test results, show that these oscillation can be reduced by the use of a windshield adhesive with a low modulus of elasticity and good damping characteristics. The test results show that the most effective way of improving the acoustics inside the passenger compartment is to employ a two-phase windshield adhesive applied by the coextrusion method. Experimental modal analysis shows that the use of a two-phase adhesive applied by the coextrusion method and incorporating a low-viscosity core can dramatically lower the overall level of vibrations in the window glass by 30–50 per cent, and in particular can bring about a flattening of the resonance peaks in the all-important roll vibration range between 100 and 500 Hz. This results in a reduction in sound levels within this frequency range of between 1 and 2 dB for rear-seat passengers.