SoundXtreme ST-503 5.25" 3-Way Coaxial Speakers

The SoundXtreme ST-503 is a pair of 5.25-inch, 3-way coaxial car speakers intended as a replacement for factory-installed speakers. It provides a compact option for vehicles that use 5.25-inch speaker locations. The full-range coaxial layout keeps the woofer and high-frequency drivers together in each speaker assembly.

This set is suited to listeners looking to refresh an aging factory speaker system or build a basic replacement system around a compatible head unit or amplifier. Its 4-ohm impedance is the common nominal load used by many car-audio systems. Confirm the vehicle's opening size, mounting depth, and connector arrangement before ordering.

The ST-503 uses a 3-way design, combining a woofer section with integrated midrange and high-frequency reproduction. This arrangement is designed to cover a broad portion of the audible range from each mounting location. The published frequency response is 100 Hz to 20 kHz, so low bass below that range is better handled by a dedicated subwoofer when deeper bass is desired.

A polypropylene mid-woofer cone and PEI dome tweeter are specified for the speaker system. The listed 20 mm voice coil and 5.3-ounce magnet are part of its compact coaxial construction. With an 88 dB sensitivity rating, output will depend on the source unit or amplifier power, installation quality, and vehicle acoustics.

Rated for 320 watts peak power, the ST-503 is intended for everyday replacement-speaker use rather than as a standalone bass solution. It can be used with a factory radio or an aftermarket system that is compatible with 4-ohm speakers. For a balanced upgrade, pair it with clean amplification and properly fitted mounting hardware.

Key Features

• 5.25-Inch Size: Fits applications designed for compact round speakers.
• 3-Way Coaxial Layout: Integrates multiple driver elements in each speaker.
• 4-Ohm Impedance: Supports common factory and aftermarket car-audio systems.
• 320W Peak Rating: Provides the published peak power-handling specification.
• PEI Dome Tweeter: Handles high-frequency reproduction within the coaxial design.
• 2.5-Inch Mounting Depth: Helps with fitment planning behind the mounting surface.

Design & Installation

The ST-503 uses a polypropylene mid-woofer cone, PEI dome tweeter, 20 mm voice coil, and 5.3-ounce magnet. Its full-range 3-way coaxial construction combines the driver elements in a single round speaker assembly. The listed outside diameter is 5.25 inches.

Check that the vehicle accepts a 5.25-inch round speaker and has at least 2.5 inches of mounting clearance before installation. Verify factory mounting-hole alignment, terminal connection type, and any required adapters separately, as fitment hardware is vehicle-specific. Use two matching speakers as a left/right pair and observe correct positive and negative polarity when wiring.