The transmission line system is a waveguide system in which the guide reverses the phase of the driver's rear output, thereby reinforcing the frequencies near the driver's Fs. Transmission lines tend to be larger than the other systems, due to the size and length of the line required by the design. The payoff is an extended low end response.
Usually, only drivers which have low Qts (0.25 - 0.4) , Qes (0.3 - 0.4) and Fs values are suitable for transmission line systems.