used each 2 m long resulting in l 9 6 u00d7 10 6 kg m 4 and l 3 6 u00d7 10 7 kg m 4 respectively data for each are presented in fig9 a and 9b in each case the small section of tubing required when connecting valve r p to the compliance has sufficient nuisance inertance to overwhelm the large compliance which was sized for the earlier experiments shown in fig7 accordingly impedance data denoted as 34 rs closed 34 have positive imaginary z as evident in fig9 a and 9b a variety of phase angles and powers delivered to the load are available using appropriate adjustments of the valves r p and r s indeed it appears that all impedances between the triangles and the circles are accessible by suitable adjustment of r p and r s fig9 b shows that the phase of z can be near 70 u00b0 even for scale powers as low as 2 w equivalent to an operating power of 32 w in a full scale helium ptr further showing the usefulness of inertance for improving the efficiency of ptrs further use of inertial effects to improve ptr efficiency is illustrated in fig4 where an acoustic transmission line 34 recovers power that would otherwise be dissipated in an orifice in previous ptrs back to volume 36 for input to compressor 14 acoustic transmission line 34 is analogous to an electric transmission line its nature is most simply appreciated by a lumped lc impedance approximation an acoustic transmission line can transmit acoustic power while changing the relative.