The ES8 is a powered subwoofer that adds low-frequency output to compact speaker systems. It uses a forward-firing 8-inch mineral-filled polypropylene cone woofer with an internal Power Port, which is intended to reduce port turbulence, noise and distortion. A Class D amplifier drives the woofer, and an auto-sensing power supply lowers consumption when the unit is idle.

Signal handling is done by 32-bit floating-point DSP with group-delay-minimizing filters and precision limiters. Integration with the main speakers is handled by an adjustable 4th-order lowpass filter (50–160 Hz) and Time-Smart Phase Control, which adjusts phase in 45-degree steps with the setting shown on LED indicators.

The subwoofer connects through an LFE input or a stereo line-level pair of RCA inputs. The cabinet measures 15.1 x 12.8 x 15.2 inches and is available in black. It is designed to match other Signature Elite speakers, such as the ES10, ES50 and ES35.