/playsound not working in commandblocks

When I use the command:
/playsound mob.wither.death @a ~ ~ ~ 2 0.1 1
I can hear it fine. But when I put it in a commandblock I can't hear the sound it makes. Now when I power the commandblock I am around 100 blocks away from it so I understand that there must be some sort of range that I can hear the sound from the command. But when I do an execute command:
/execute @a ~ ~ ~ /playsound mob.wither.death @a ~ ~ ~ 2 0.1 1

It still doesn't work. Shouldn't this work?
This is my bug. Sorry if it isn't a bug and I have just made a silly mistake in the command. Thanks