incorporate equalization networks (e.g., Zobel networks) that compensate for the changes in impedance with frequency inherent in virtually all loudspeakers. The issue is complex, as part of the change in impedance is due to acoustic loading changes across a driver's passband.

Two disadvantages of passive networks are that they may be bulky and cause power loss. They are not only frequency specific, but also impedance specific (i.e. their response varies