What is the sound’s origin of an audible Alarm targeting a cubic area?

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.

$ [\dots]$

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.