Sounds like something a bartender might ask you. Instead, it's a question relating to subwoofers and our home music systems.
When subwoofers first appeared as separately purchasable products, the convention was to implement only a single sub. As they became more popular and as subwoofer manufacturers wanted to sell twice the number of products, two subs came more in vogue.
My first subwoofer, an M&K, was a single device, hopelessly attempting to integrate with a pair of Acoustat electrostatic loudspeakers. It lasted perhaps a week before going onto the used market. Adding a second subwoofer in this case would only have heaped insult onto injury.
But as subwoofers got better, the idea of using them to augment our systems' foundation became accepted and today, whenever I implement a subwoofer, it's always a stereo pair. Well, actually, that's not entirely true. This subject deserves a little deeper explanation. We've discussed much about subwoofers as of late, and I've been asked to continue the discussion a bit further, following my recent revelations of a misbegotten youth. Seems you'd prefer to read of subs than lie detectors. I don't blame you.
We've previously touched on servos, crossovers, drivers and enclosures. Tomorrow we'll look at one vs. two in the music system.