Five high frequency annular thermoacoustic traveling wave devices have been developed and characterized. A 1.27 cm bore diam 2 kHz engine was optimized, increasing its maximum acoustic output from 140 to 167 dB. A new 1.60 cm bore diam 2 kHz engine has been assembled with the expectation of even higher acoustical power output because power is proportional to cross-sectional area. In the 3 kHz regime, two geometries were investigated, an oval shape and more square version, which is easier to assemble. These devices were found to have comparable outputs suggesting that the square geometry is a viable alternative, and, thus, all additional devices were constructed this way. A 4 kHz engine was also studied. In order to measure the effects of the heat exchangers and regenerator assembly on the acoustic flow, a resonator tube was constructed. This tube was fitted with the device innards and driven by a speaker. An absorption coefficient of 0.4 was measured. This information along with the 916 T across the regenerator allows for an estimate of the limit on the acoustic gain of the system to be calculated. [Research supported by the U.S. Army Space and Missile Defense Command/U.S. Army Forces Strategic Command.]