The acoustic characteristics and physical absorption mechanism of the sound absorbing panels with deep subwavelength thickness are studied，and the possibility of further improving its low-frequency performance is also discussed. The absorber unit is a double layer perforated panel absorber that is constructed by inserting a separating plate with a small hole into the coiled coplanar air chamber which is bent in the Archimedean spiral. By adjusting the location of the separating plate in the chamber，it is found that the resonance frequency of the absorber can be easily tuned over a large bandwidth while the structural parameters are fixed， and do not change its near-total absorption properties. A complete mathematical model of the absorbing panel that describes its absorption characteristics is derived，and the physical absorption mechanism of the panel is also revealed by numerical simulation.Meanwhile，the effects of structural parameters on the absorption characteristics are also investigated，which provides a basis for further improving its low-frequency performance. To verify the validity of the research conclusion，samples have been designed and fabricated by 3D printing，and the results are all in good agreement. Compared with the previous techniques，near-total absorption can be received at a lower frequency.