The better it works ...

If you think about it, the greater the impact something has in your system, the more important its role in your system. That might seem obvious, and it is, but it's important to review again. An example would be subwoofers. If you add a sub to your system and that system's transformed, I would suggest that the level of transformation indicates the degree of bass deficiency of your main speakers: the more it helped, the more you needed it. Why's this important? I think it helps debunk the myth of 'full range loudspeakers' some manufacturers have been trying to convince us of for years. I can't tell you the number of times I've visited people who proudly show off their 'full range' home audio system to me that I have to disappoint with the news they're missing the bottom octave. Sure, it sounds like it goes low, but until you hear it actually go low, there's no point of reference to make a judgment; unless you know intimately the sound of, say, a pipe organ. But now onto the question of one vs. two subs. In yesterday's post I suggested a formula I use is small room, small speakers = one sub. Large room, large speakers = two subs. In a decent sized room with 'full range' loudspeakers, a subwoofer on each side, fed separate left and right signals from the preamp or DAC, works well because of the room's larger size. Most of the directional cues for bass tend to be higher frequencies that come from the main speakers so having it on one side or the other has minimal impact on the soundstage directionality. But keeping the low frequency pressure even in a large room can be aided with the addition of the second subwoofer. Perhaps the biggest trick with any configuration of a subwoofer is keeping the crossover low pass filter as low as you can manage. It should be high enough to fill in the midbass areas of double bass, cello and big brass (if they need it), yet not so high that it draws attention to itself in the room. Make sure you never hear the sub - that all bass seems to come from the main speakers - and when an organist places her foot on the 16Hz pedal, that ought to rattle you and everything in the room. Just like you were there.