In JJS, there usually isn’t a built-in “slow down” button for boombox audio, so the practical answer is to use a slower version of the sound file or a playback-speed trick outside the game. Community posts suggest players are looking for the same thing, but there isn’t a clear universal in-game method.

What people usually do

  • Upload or prepare the audio at a lower speed before using it in-game.
  • Use an external audio editor or speed changer to make the track 0.5x, 0.8x, etc.
  • If the game/server has a specific boombox or sound block mechanic, check whether it supports pitch or speed changes, since some effects can alter how boombox music sounds.

Fastest workaround

  1. Take the song you want.
  2. Slow it down in an audio editor or online speed changer.
  3. Export the new file.
  4. Use that slowed file with your boombox setup.

Important note

If you mean a specific JJS feature, the exact method depends on whether that version allows sound editing, pitch shifting, or only preset audio IDs. Recent forum chatter suggests many players are still treating it as limited or impossible in the base game.

TL;DR

There doesn’t appear to be a standard in-game way to slow boombox audio in JJS; the usual solution is to slow the audio file itself before using it.