The Alarm spells reads as (emphasis mine)
You set an alarm against unwanted intrusion. Choose a door, a window, or an area within range that is no larger than a 20-foot cube. $ [\dots]$ . You also choose whether the alarm is mental or audible.
An audible alarm produces the sound of a hand bell for 10 seconds within 60 feet.
If I choose to cast an audible Alarm targeting a door or a window, the description is pretty clear: the sound can be heard within 60 feet from that object, i.e. within a sphere$ ^\dagger$ centered in the object and with radius 60 feet.
What will the sound’s origin be if I target a cubic area whose side is strictly greater than 5 feet?
$ ^\dagger$ I always consider the 3rd dimension.