Just couple of points about the article.
1- the main focus of the study is to silence the sound while maintaining ventillation, i think comparison with the barrier is not relevant.
2- the structure is deep subwavelength compare to the mufflers size
3- low frequency can still be silenced with this design but need an stiffer material maybe metal
4- experiment is design considering both fabrication limitation ( 3D print size) and the tube material to be effectively work as a waveguide