Double bass arrays keep high efficiency despite half the units cancelling

Evidence

Even though half of the subwoofers are simply cancelling the other half, this method does not seem to have lowered efficiency much, since it minimizes both peaks and dips. Another advantage is that the specific location of seating area is not critical, since you theoretically only have a plane wave—at least at the lowest frequencies. A disadvantage is the inconvenient subwoofer locations required. — Toole, Floyd E, Sound reproduction- the acoustics and…, 1608

Categorization

• QUESTION: Counterintuitive that deliberately cancelling half the array’s output doesn’t seriously hurt efficiency — worth understanding the mechanism behind the peaks-and-dips minimization.