Comparison between measured TL_an of the gas resonator with p₀ = 3.4 bar and p_f = 5.5 bar for the 20 m PU tube termination (a) and the closed-end termination (b) using the source-side multi-microphone method with robust formulation, the standing-wave method and the classic multi-microphone method with robust formulation. The measured TL_an are compared to undamped analytical model, damped model with quality factor Q = 1.5 and an frequency adjusted TL_an plot with Q = 1.5 and f_max = 9.0 Hz.