Abstract: An acoustic pyrometer measures the average gas temperature across a space of known distance, especially turbulent, high temperature gas loaded with caustic particulates. It includes an acoustic signal generator that generates a high amplitude acoustic signal with a short rise time The acoustic signal generator includes an outer tank closed at top and bottom ends by top and bottom end walls and enclosing an outer chamber. A cylinder is supported within the tank and has top and bottom opposed ends. A mid-plate extends across the cylinder and defines the bottom end, and an axial opening in the mid-plate receives a shaft of a piston assembly having an upper piston and a lower piston at ends of the shaft. A throat is attached to the bottom end, and receives the lower piston. The lower piston seals the throat when received in the throat. The upper piston is slidable in the cylinder under influence of air pressure.