Lets take a look at the performance capacity of the baby grand verses grand pianos.
Voice of the small baby grand piano (4’10” to 5’6”) is distinguishable from the larger grand piano (5’8” or longer).
Longer strings of grand piano, allow frequencies to resonate from a larger surface area, resulting in a more balanced, full-bodied tone.
The grand piano’s signature timbre is partially reliant on the length of its strings and soundboard (along with the quality and workmanship of these parts).
Most of the concert halls have 7 feet or longer grand pianos present on the stage.