SoundXtreme ST-AP6 1/2 DIN Digital Bass Processor

The SoundXtreme ST-AP6 is a 1/2 DIN digital bass restoration processor for adding adjustable low-frequency enhancement to a car audio signal path. It is designed to recreate low-frequency information and provide dedicated bass processing before the signal reaches an amplifier. This makes it a practical addition for systems that need more control over bass character than a head unit alone provides.

The processor is intended for use between an audio source and amplifier through its stereo RCA connections. Its balanced-input design is specified with 60 dB noise rejection to help maintain a stable signal in a mobile-audio installation. With up to 13.5 volts of output level, it is built to provide a strong processed signal to compatible amplifier inputs.

Adjustment is centered on the main-unit Wide and Sweep controls, along with the included dash-mounted remote. Sweep selects the bass-restoration center frequency from 10 Hz to 100 Hz, while Wide adjusts the range of frequencies affected. The remote places Bass Level and PFM subsonic-filter adjustment within reach of the driver.

A PFM subsonic filter is included to reduce ultra-low-frequency content that can place unnecessary demand on a subwoofer system. Its adjustable range is specified from 35 Hz to 80 Hz. This allows the processor to be tuned around the capabilities of the installed subwoofers and enclosure.

The ST-AP6 uses a PWM high-headroom power supply, gold-plated signal contacts, and a lighted bass-restoration display. Published performance figures include a 10 Hz to 100 kHz frequency response, 0.003% total harmonic distortion, and a 130 dB signal-to-noise ratio. It is suited to a system upgrade where bass restoration, signal processing, and accessible level adjustment are desired.

Key Features

• Digital Bass Restoration: Recreates low-frequency information in the audio signal path.
• Parametric Bass Adjustment: Wide and Sweep controls tailor the processed bass range.
• Dash-Mount Remote: Places Bass Level and PFM filter adjustment near the driver.
• PFM Subsonic Filter: Reduces ultra-low-frequency content below the selected filter point.
• 13.5V Output Level: Provides a high-level processed signal for compatible amplifiers.
• Balanced Input Design: Specifies 60 dB of input noise rejection.

Design & Installation

The ST-AP6 has a compact 1/2 DIN processor chassis with mounting ears, a power-status LED, front-panel bass controls, gold-plated RCA signal connections, and a dedicated remote-control connection. Its PWM high-headroom power supply supports the processor's stated output capability. The included dash remote has separate controls for Bass Level and the PFM subsonic filter.

Install the processor in the signal chain between the source unit and amplifier, connecting the source to the left and right RCA inputs and the amplifier to the left and right RCA outputs. The unit requires constant +12V power, a solid chassis ground, and a remote turn-on connection; use an appropriately sized inline fuse near the battery. Mount the remote where its controls can be safely reached, then begin tuning with conservative bass and amplifier-gain settings.