The Buick Century rear door panel accommodates a 4x6 inch speaker size. Full-range units represent the compatible type for the rear door panel location. These specifications cover the 1991 model year.
A single driver that reproduces bass through treble without a separate crossover network. It is the simplest replacement option and is common in factory audio systems.
Additional Notes
The rear door panel location in the 1991 Buick Century accommodates a 4x6 inch speaker cutout, an oval-format mounting space that differs dimensionally from both standard round and larger rectangular configurations.
The 4x6 inch oval format produces an elliptical cone area that distributes sound across a wider horizontal axis than a circular 4-inch driver, making the rear door panel a broader radiating surface relative to its smaller round counterparts.
A rear door panel mounting position places the speaker low and to the side of the cabin, directing sound toward the lower portion of the passenger compartment rather than at ear level.
The door panel cavity introduces baffle characteristics determined by the door's internal structure, where the depth and material of the door shell influence the low-frequency loading of any driver mounted in the 4x6 inch opening.
Full-range drivers are single-unit speakers designed to reproduce the entire audible frequency spectrum - typically spanning from around 80 Hz to 20 kHz - within one cone assembly, without the need for a separate crossover network.
In the rear door panel position of the 1991 Buick Century, a full-range driver handles both midrange vocal frequencies and upper treble detail from a single cone, which is relevant given the location's distance from front-seat occupants.
The 4x6 inch driver size, relative to smaller 3.5 inch units, supports greater cone surface area and therefore more displacement, which corresponds to improved low-midrange output from the rear door position.
Full-range compatibility at the rear door location indicates the factory wiring and mounting provisions for the 1991 Buick Century are configured for a single-driver solution rather than a component system requiring separate tweeter placement.