This paper deals with active control of sound transmitted power through panel. It is well known that the sound transmission loss is dependent on mass of sound insulation materials. So, it is difficult to reduce noise at low frequency with light panel. In our previous work, we proposed new simpler way with feedforward modal control to reduce sound transmitted power at low frequency. In this work, the mechanism of the proposed method is discussed using power mode. Then experimental results are shown, demonstrating the validity of the proposed method.