How do I make people able to hear a sound played using commands regardless of where in the world they are?

I'm making a map. i am trying to use the /playsound command. There is going to be a boss battle at the end, and I need my music disc to play. I know how to play a sound, but I want it so people can hear it no matter where they are in the final boss area. Because if they walk far enough away, they won't be able to hear it.

Arguments Used

For the target selector use @a this will play the sound to all players. Then, for the volume argument, put in something like 999, this will create a large sphere of audio.

Example

I use a /execute to get the proper location of a player.

/execute @p ~ ~ ~ /playsound mob.enderdragon.growl @a ~ ~ ~ 999