What would be a typically recommended size for a passive radiator?
The PR should have a minimum of 2 times the volume displacement (Vd) of the active driver. If your woofer displaces 2L at Xmax, then you will want to have a passive, or passives that displace 4-8L to make sure you do not run out of excursion at the low frequencies. Typically most people use a passive one standard size larger than the active driver (e.g. 12″ passive with a 10″ driver). Some choose to add multiple passives to increase the passive area to the limit. You can use multiple PR in the same enclosure, but then you will need to ensure that the Fs of each are as close as possible. We prefer to use dual opposing PR as this allows the PR to mass cancel their moving mass, very important for keeping the cabinet from shaking.
