@quanghuy147
Numerous other design parametres are also invlovled, but let's not complicate the issue!
For difficulties in reproducing low frequencies through smaller drivers, see Shadorne above.
To make the situation more complicated, some speakers have small drivers but there are many of them. Can many small drivers compensate for the size limitationYes, they can, but it's a whole different design ball-game! Generally, smaller diaphragmes are lightweitgh & therefore move faster but, being smaller, they reproduce lower frewuencies at an imperceptibly low amplitude (volume).
I don't know which specs determine a wide sound stageThe wide s-s is usually the result of efficient driving (i.e. small speakers) and a small baffle (small-sized speakers).
Numerous other design parametres are also invlovled, but let's not complicate the issue!
For difficulties in reproducing low frequencies through smaller drivers, see Shadorne above.