I’ve run a single sub + 2 desktop main speakers for ~15 years. Until ~5 years ago the mains were powered; then I switched over to a series of passives.
For me, the hard part of subs wasn’t placement--I only had one placement option, and luckily all the subs I’ve tried sounded good in that spot. Specifically, in my nearfield setup (home office), the sub’s effect sound flattest/best in the listening seat equidistant from the speakers. So I lucked out there.
But for me, the hard part was getting a high-pass filtered signal to the mains. Some subs have built-in crossovers that can do this. Sometimes those crossovers are high quality and sound good; other times they’re trash and sound bad (I’ve had both). I solved that issue for once and for all by picking up a transparent, high-quality external electronic crossover ((Marchand XM-66 in which the high- and low-pass filter slopes 24 dB/octave).
The other hard part is matching the sub’s output level to that of speakers. I found two things that help:
- I get better results by far when using sealed/acoustic suspension speakers. They sound better here, and have the benefit of having a real drop-off out output at the resonant frequency. I count on that when setting the crossover
- And it helps to cross over to the sub at the lowest frequency (that is comfortably above the -3 dB drop-off point of the mains).
Would all this apply to a far larger, high-end system in a living room? Yes, but also no, because there the physical placement of the sub (or subs) would consume much time & effort.