The GMC S15 behind seat location accommodates a 4x10 inch speaker size. Full-range units represent the compatible type for the audio system. These specifications cover the 1990 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 GMC S15 is a rear cabin position typically situated along the back wall of the cab, behind the occupants, where speaker depth and mounting clearance are constrained by the cab structure.
A 4x10 inch speaker is an oval or rectangular format with an elongated cone surface area, a shape that allows for a wider low-frequency radiating surface within a shallow or narrow mounting cavity compared to a round equivalent.
The 4x10 inch format's extended horizontal dimension suits the behind-seat panel geometry found in compact truck cabs, where vertical space is limited but horizontal span along the rear cab wall accommodates the longer axis of the speaker.
The behind-seat position places the speaker firing toward the front of the cab, meaning the driver and passenger receive sound from behind, which affects stereo imaging and perceived directionality relative to front-mounted sources.
The 4x10 inch cone area, being larger than a standard 4-inch round but smaller than a 6x9 inch oval, produces a mid-bass response that is moderate in extension, typically covering frequencies from roughly 80 Hz up through the midrange.
Full-range speakers are drivers designed to reproduce the entire audible spectrum from a single cone, covering low, mid, and high frequencies without requiring a separate crossover network or supplementary tweeters.
In the behind-seat location of the 1990 GMC S15, the full-range type is the only compatible specification, meaning a single driver handles all frequency reproduction at that position without supplemental high-frequency components.
The 4x10 inch full-range driver's cone mass and size make high-frequency dispersion less precise than a dedicated tweeter, as larger cones exhibit increasing directionality at higher frequencies due to their physical dimensions relative to short wavelengths.
The behind-seat mounting depth available in the GMC S15 cab determines the maximum magnet and basket depth a 4x10 inch full-range driver can accommodate, making mounting depth a critical compatibility factor for the GMC S15 behind-seat position.
Full-range drivers in a 4x10 inch format typically use a whizzer cone or treated surround to extend upper-frequency response, compensating for the inherent high-frequency rolloff of a larger cone operating without a separate tweeter.