Large room = At least 6.5 metres x 8.5 metres x 4.5 metres (height) but unlikely to have a hobby like hifi in it as this room will be used too regularly by family and guests and will have too many large windows, rugs, large furniture, bookshelves and will be of a more formal nature in use. Any music in a room this size is more likely to be live if the family is musical.
Hifi is most likely to be located in a den or study or spare room or converted out-building well away from the main living/sleeping areas/servant quarters.
I've had customers with houses like that, and the acoustics were dreadful, very uncomfortable to talk in as your voice echoed all around the house, as the saying goes, it's not the size that matters but what you do with it!!Hahaha.