Loudness estimation in the presence of vertical vibrations

The goal of the study was to check whether vibrations submitted to a subject can modify his loudness evaluation. For that purpose, the subject was seated on a rigid chair vertically moved by a shaker, at the frequency of 28 Hz and at 6 different levels. He was also exposed to a pure sound: either a 28 Hz tone produced by a subwoofer, or a 1000 Hz tone produced by headphones. For each combination of sound and vibration levels, the subject had to estimate the magnitude of the loudness of the tone, as compared to a reference tone, heard without any vibration excitation. He also had to evaluate the magnitude of vibration using a 10 point scale. Twenty subjects participated in the experiment. The results showed that vibrations did not influence loudness estimation. On the other hand, the estimation of vibration level was significantly influenced by the level of the 28 Hz pure tone, which can indicate an interaction between the perception of sound by the body and the perception of vibrations.