It’s because most ‘subwoofers’ are glorified fart boxes that have terrible harmonics, coupled with the fact that placing a subwoofer in the wrong spot can creat

It’s because most ‘subwoofers’ are glorified fart boxes that have terrible harmonics, coupled with the fact that placing a subwoofer in the wrong spot can create poor room frequency response. Two subwoofers is preferred. Four subwoofers is the sweet spot. Any more and you get diminishing returns. Full-range speakers can work for a lot of music because most music has hardly any information below 40 Hz, the point where many ‘full-range’ speakers become inaudible. For content with significant sub–80 Hz content (i.e. movies, organ music, and Drum & Bass), subwoofers are more economical and arguably better for several reasons. One, bookshelfs+1 or 2 subwoofers is cheaper than all five full-range. Two, the subwoofers will offload power from the amp. Low frequencies have a tremendous amount of power in typical sounds. Three, the subwoofers can be placed anywhere so long as the cutoff frequency is set to 80 Hz or less. Above 80 Hz, the consensus is that the sound becomes locatable. The arbitrary placement of subwoofers is important because it allows you to place the subwoofer in a place which will excite room modes or attenuate room modes such that a more desirable room response is achieved. These positions are usually not where you would want to place speakers.