Since the phase angles of three types of regenerators were almost the same shown in Fig. 7, the difference between the net output acoustic powers with three regenerator types was mainly determined by flow resistance loss. Fig. 8 gives the amplitudes of the pressure waves in the UM 729 and expansion spaces with different load resistances. Because the displacement of the alternators were fixed at 6 mm, the pressure amplitudes in the expansion space represented by dashed line in Fig. 8 were quite similar.