Sound Absorption Performance of Membrane Covered Insulators 2001-01-1455
Molded fiberglass hood insulators (hoodliners) and engine side dash insulators (dashliners) are widely applied in vehicles for noise control. These absorptive components reduce reverberant “build-up” in the engine compartment and thus cut the noise transmission into the passenger compartment. Due to restrictions of underhood space, the hood and dash insulators normally have limited thickness (under 1.5 inches), which results in inadequate noise absorption coefficient in mid and low frequencies (100Hz - 2000 Hz), where the peak of engine compartment noise spectrum exists.
It is known that covering the porous absorptive panel (at the noise incident surface) with an impermeable membrane will increase the mid-low frequency absorption coefficient of the panel at the cost of some high frequency absorption coefficient loss.