An experimental investigation of a hybrid active/passive panel for increased transmission loss at low frequencies

The control of sound transmission through panels is an important noise control problem in the aerospace, aeronautical, and automotive industries. The trend in using lightweight composite materials that have low sound isolation performance is a negative factor regarding the partition low frequency transmission loss. Double-panel partitions with the gap filled with sound absorption material are often employed to improve the sound isolation performance with reduced added weight penalty. However, in the low frequency range the strong coupling between the panels through the air cavity and mechanical paths greatly reduce the sound transmission performance that is lower than the performance of a single panel system at some frequency ranges. In this work an experimental investigation of a new kind of hybrid (active/passive) acoustic actuator is presented to replace the current acoustic absorption foam material, aiming to improve transmission loss in the low frequencies using active control, without altering the passive attenuation of the foam. A prototype of the system is tested in a plane wave acoustic tube setup. A feedforward control system was setup to control the sound power transmission of the active-passive panel at an error microphone and a particle velocity sensor downstream of the sample. Measurement results of the passive and the active transmission loss measurements using a transfer matrix approach are presented.