What subwoofer should I pair with the GZRA MICRO ONE?

A single subwoofer rated around 250 to 350 W RMS at 2 ohms fits its output. A 4-ohm sub gets 220 W RMS. Match the sub's RMS rating to the amp's 2-ohm figure so you have headroom.

Does it fit in a small space?

Yes. At 75 x 44 x 190 mm it is one of the smaller monoblock amps, so it fits under seats, in side panels and in motorcycle or ATV builds where a full-size amp will not go.

What do the subsonic and lowpass filters do?

The subsonic filter cuts frequencies below 15 to 25 Hz to protect the sub from ultra-low excursion. The lowpass sets where the sub rolls off, adjustable from 40 to 400 Hz.

How do I set the input sensitivity?

The gain range runs from 200 mV to 5 V, so it accepts both low-level RCA signals and higher-voltage sources. Set gain with the head unit at about three-quarters volume to avoid clipping.