With your back to the funerary monument, walk through the room towards the door in front of you and enter room n. 23, called “Sala delle Cantorie.” Here you will find two “cantorie,” one designed by Luca della Robbia (on your right) and one designed by Donatello (on your left), in the 1430s. Try standing in the middle between the two, so you have the best view for a comparison.