In both transmission line and bass-reflex loudspeakers, the designer generally intends for midrange energies entering the cabinet to be attenuated so that they are not present. Low-pass filters formed by acoustic insulation and by woofer crossover components both serve to reduce energies that energize unwanted higher-frequncy resonances. But for what energies are within the cabinet, the major issues are caused by standing waves, which is the property transmission lines are based upon.

You may be interested in the paper called Acoustic Filters, Waveguides and Transmission Lines, by Daniel Russell.