Sound intensity measurements in a vehicle's interior sound field

Sound pressure and sound intensity in the passenger compartment of a vehicle with many standing waves are measured through piston-plate excitation. These measurements provide the characteristics of attenuation in the free field near the sound source, which is found to be approximately −6 dB per doubling of distance. At a certain distance from the sound source, sound intensity shows an average sound-pressure level between the maximum and minimum values in the passenger compartment. The reason for this is that, owing to the use of sound-absorbing materials, the sound field does not consist only of standing waves, It is revealed that progressive waves dominate near the sound source. As a result, sound intensity measurements in passenger compartments provides the precise location and contribution of the sound source, even when booming sounds are present. Moreover, using the modal analysis method to investigate the behavior of the body vibration from the enforced point to the sound source is effective in improving the body structure for reducing passenger compartment noise levels.