A large speaker system generally has large drivers with some space between them. The sound from the different drivers (at different frequencies) must blend, and the greater the distance between drivers the greater the distance must be between the speaker system and the listener.
Why should some speakers need a big room?
It's often said that some speakers need a big room to perform well. Couldn't you just turn down the volume? And if the speakers don't sound nice at low levels, isn't this a fault with the speakers?
(And I never heard any say a pair of headphones needed a big head...)
(And I never heard any say a pair of headphones needed a big head...)