The Focal Utopia has a single full range beryllium driver, but there many headphones that use more than one driver. For example, 1More has an over-ear headphone with 3 drivers and an in-ear headphone with 4 drivers. Some in-ear monitors such as from 64 Audio have as many as 18 balanced armature drivers.
MMM. i guess i meant to say "most" headphones. Iems are not headphones. Either way a single full range driver is easier to do on headphones than it is do on a speakers is my main point.