.....that would be 9, "four and 1/2 inch drivers", in the 901....four 901's positioned correctly, using two Bose 901 equalizers and the Bose 1801 amp sounded great, trust me....the problem with that setup this day and time would be no surrounds....Bose began with the 901, added the 301's, 501's, 601's, 701's, and others....then, Bose woke up, and began the Accoustimass cubes....the rest is history....women will see to it that Bose stays solvent with the cube sales.....