The Mercury Topaz rear deck lid accommodates a 6x8 inch speaker size in that location. Full-range units are the compatible type for the audio system in that position. These specifications cover the 1985 to 1994 model range.
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 deck lid is a horizontal surface positioned at the base of the rear window, behind the rear seating area, situating speakers to fire upward toward the cabin interior.
Mounting at the rear deck lid places speakers in a location acoustically distant from front-seat listeners, which makes the low-to-mid frequency reproduction capacity of a 6x8 inch driver relevant for projecting sound across the cabin length.
The 6x8 inch oval format fits within the spatial constraints of the Mercury Topaz rear deck lid across all listed model years, with the elongated oval shape accommodating the shallow, flat mounting surface typical of rear decks in compact sedans.
A 6x8 inch driver produces a larger cone surface area than a standard 6.5 inch round speaker, which increases low-frequency displacement and allows for greater bass output without requiring a separate subwoofer in the installation.
The oval geometry of a 6x8 inch speaker distributes cone movement across two axes, which affects the directionality and dispersion pattern of mid-range frequencies radiating upward from the deck lid position.
Full-range speakers are single-driver units designed to reproduce low, mid, and high frequencies from one cone assembly, making them suited for installations where only 1 speaker location per channel is available, as is typical of a rear deck lid configuration.
In a rear deck lid position, a full-range driver handles the entire audible spectrum without a crossover network, meaning the single cone must manage both the bass frequencies reinforced by the 6x8 inch cone area and the treble frequencies that benefit from forward dispersion toward seated occupants.
The Mercury Topaz rear deck lid opening is sized to a 6x8 inch footprint across all model years listed in the specifications, indicating a consistent chassis dimension for the rear deck speaker cavity throughout the production range represented.