As we can see from Figure 16 this helps to control the excursion of the cone in a greater frequency range than the BR, which, in this respect, operates mainly at the tuning frequency. The two systems are both driven with a 6 volt amplitude sinusoidal sweep, but we note that the BR, while better controlling the cone excursion at the resonance, limiting it to only 1.5 mm, reaches the 4 mm limit excursion of the RS100-4 at 56 Hz against the 25 Hz of the TL. Also note that the transition from flat response curve to steepest slope is much smoother in the TL than in the BR. I think these are the aspects that lead to the typical dry and controlled bass of the transmission lines, without any trace of the pumping that can be perceived by some not too well designed bass-reflex systems.