(20%) 2. A plane wave impedance tube with length L and an excitation piston vibrating with a frequency of @ at one end is used to measure the impedance of the test specimen at the other end. Please show and plot the average acoustic power (or log10 ) distribution along the tube, if the specimen is (1) a perfectly absorbent reflective surface, (2) an ideal acoustic rigid surface, (3) open to the atmosphere.