The bug
Explosions are played at a fixed full volume a in 32 block radius. After leaving the radius, the sounds do have a falloff, although only for a few blocks outside the 32 block radius.
Other sounds work as intended.
How to reproduce
Have a dispenser fire tnt
Start walking away
Related issues
relates to
Comments

Bells are now tracked in MC-270336
Updated: Elaborated on explosion sounds. They do have a small falloff distance outside of the 32 block radius, but are also full volume inside of it.