Bug //ETERNAL EDIT - bug has been fixed.
If a player is at 140 blocks from a playing Jukebox Car , 1 second of the audio plays then stops. Progressing closer to the Jukebox Car the audio will play normally at the set distance .

Enhancement
Variable Distance would be good , if the jukebox car is at the front of the train and the train is long , no music is heard in caboose . Have the radius distance variable adjustable in the GUI or config file.

We already have a radius for our jukebox cart

EntityJukeBoxCart: line 93.
if we do have a variable distance, then we aren't using it, all it does is change volume within a set distance.

The volume issue should be fixed as of 1ea693a

Also due to a github glitch, I should mention that I was the one to change the issue name.

There is still a bug .If you leave the map with the Jukebox playing , then log in any where on the map 1 sec of audio plays at max vol. Entering into the edge of loaded chunks with a jukebox car playing music will play 1 sec of audio at max vol then stop .

@Tsoccerguy3 we are in knowledge of this bug and this will be pushed to the rewrite since we have some more bugs with that Jukebox Car. That's why we decided to remove it until someone added it back in.