Experimental Investigate of Dispersion of Sound Speed in Low-pressure Air

Experimental data on the sound speed in rarefied air are limited. We employed an environmental simulator to realise a low-pressure (200-10
⁵
Pa) air environment. The pressure control precision of the environmental simulator reached ± 10 Pa, and the temperature uniformity is ±5 °C. Transducers of three different frequencies (21 kHz, 34 kHz, 40 kHz) are used to measure the sound speed. The results demonstrated an increasing trend in the experimental sound speed as the pressure decreased in the air. Furthermore, a decrease in dispersion is observed with lower temperatures. The qualitative consistency between theoretical analysis and experimental results was evident. However, the theoretical understanding of sound speed in air is intricate, influenced by various gas components such as trace amounts of water vapor and carbon dioxide. Quantifying experimental results through theory remains challenging.