 The frequency response of a passive radiator will be similar to that of a ported cabinet, but the system low frequency roll-off will be slightly steeper due to a notch (dip) in frequency response caused by the Vap (compliance or stiffness) of the passive radiator.This notch occurs at the PR's free-air resonant frequency and causes slightly poorer transient response.Despite this, perhaps due to the lack of vent turbulence and vent pipe resonances, many prefer the sound of PRs to reflex ports.