The Ford F-Series Super Duty behind seat location accommodates a 6x8 inch speaker size. Full-range units represent the compatible audio type for the system. These specifications cover the 1999 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 behind-seat location in the Ford F-Series Super Duty places speakers in a confined enclosure behind the cab's rear seating area, a position that typically limits depth clearance and affects baffle surface area available for mounting.
A 6x8 inch speaker fits an elongated oval mounting cutout, and the asymmetric cone shape distributes excursion across a larger surface area than a round speaker of equivalent minor-axis diameter would allow.
The 6x8 inch format's extended horizontal dimension allows for greater low-frequency cone displacement relative to a smaller round driver, which is relevant in a behind-seat enclosure where the speaker must project sound forward through or around the seat structure.
The behind-seat position in a cab typically places the speaker at or near floor level relative to the occupants, meaning the driver operates in a somewhat acoustically obstructed path toward the listening area.
Full-range drivers are designed to reproduce the entire audible frequency spectrum from a single driver unit, covering low, midrange, and high frequencies without a crossover network splitting the signal to separate drivers.
In a behind-seat installation, a full-range driver handles transient midrange content such as vocals and instruments alongside low-frequency output, which requires balanced cone stiffness and surround compliance to avoid distortion across the frequency span.
The 1999 Ford F-Series Super Duty behind-seat position accommodates a 6x8 inch full-range speaker, a pairing in which the driver's larger radiating surface supports lower-frequency extension that a smaller full-range unit in the same location would not reproduce as effectively.
Full-range drivers used in a behind-seat position without supplemental tweeters must rely on cone breakup or a whizzer cone to extend high-frequency response, since the primary cone's mass limits treble dispersion at higher frequencies.
The 6x8 inch mounting footprint requires an oval cutout with a minor axis of approximately 6 inches and a major axis of approximately 8 inches, dimensions that determine frame compatibility with the factory mounting plate in the behind-seat panel.