The performance of an ultrasound reactor chamber relies on the sound pressure level achieved throughout the system. The active volume of a high frequency ultrasound chamber can be determined by the sound pressure penetration and distribution provided by the transducers. This work evaluated the sound pressure levels and uniformity achieved in water by selected commercial scale high frequency plate transducers without and with reflector plates. Sound pressure produced by ultrasonic plate transducers vertically operating at frequencies of 400kHz (120W) and 2MHz (128W) was characterized with hydrophones in a 2m long chamber and their effective operating distance across the chamber’s vertical cross section was determined. The 2MHz transducer produced the highest pressure amplitude near the transducer surface, with a sharp decline of approximately 40% of the sound pressure occurring in the range between 55 and 155mm from the transducer. The placement of a reflector plate 500mm from the surface of the transducer was shown to improve the sound pressure uniformity of 2MHz ultrasound. Ultrasound at 400kHz was found to penetrate the fluid up to 2m without significant losses. Furthermore, 400kHz ultrasound generated a more uniform sound pressure distribution regardless of the presence or absence of a reflector plate. The choice of the transducer distance to the opposite reactor wall therefore depends on the transducer plate frequency selected. Based on pressure measurements in water, large scale 400kHz reactor designs can consider larger transducer distance to opposite wall and larger active cross-section, and therefore can reach higher volumes than when using 2MHz transducer plates.