ABSTRACT
A dipole subwoofer does neither of these things; instead the rear radiation is allowed out into the room without modification. Typically one or more large-diameter drive units are mounted on a relatively small baffle, as in Figure 15.1g; this means that the bass will begin a 6 dB/ octave roll-off relatively early, because of cancellation around the edges of the baffle. To counteract this, drivers with a high Qts are sometimes used to give a peaky underdamped response that lifts the overall response before roll-off; adding dipole equalisation to an active crossover is a far better approach as it gives complete controllability and eliminates the need for special drivers that may be hard to get. This usually consists of a low-frequency shelving characteristic, where the amount of boost plateaus at low frequencies to avoid excessive cone excursions; more details are given in Chapter 11 on equalisation.
