How low does the Thump18Sv4 go?

Mackie rates it down to 25 Hz, so it reproduces deep sub-bass for electronic music, kick drum and bass guitar. Real output at the very bottom depends on the room and placement.

Will it work with non-Mackie speakers?

Yes. Besides the Thump 12, Thump 15 and Thump GO presets, it has a variable crossover you can set to match other tops. Use the high-pass outputs to send mids and highs to your satellites.

Can I pole-mount a speaker on it?

It has an M20 threaded socket for a mounting pole, so you can put a satellite top above the sub. Check the weight of the top against the pole's rating.

Does it have a built-in mixer or DSP?

No. It offers level, phase invert, mono/stereo modes and crossover settings, but no channel EQ or presets beyond the crossover modes. Pair it with a mixer for tone control.

Is one enough for a band or DJ set?

For medium rooms, one unit adds solid low end. For larger venues or heavy bass music, two units give more even coverage and headroom.

How do I connect it to my system?

Run balanced XLR from your mixer into the sub, then use its high-pass outputs to the tops and full-range outputs if needed. Set the crossover to match your tops.