The noise transmission loss characteristics of 28 flat, fiber reinforced, composite panels and 4 aluminum panels, with dimensions of 24.1 cm by 40.6 cm, have been experimentally investigated in the NASA Langley Research Center noise transmission loss apparatus. To support the acoustic data, modal frequencies and modal damping for several mode shapes of each of the test panels were extracted experimentally, using impulse testing with a Computer Aided Test system. It was determined that the modal frequencies and damping ratios are affected by the fiber orientation in the composite panel. The transmission loss of composite panels is compared with that of aluminum panels of equal critical shear load. The effects of applying structural foam and damping material are indicated.