0 a small electronic device that plays music and has headphones so that you can listen to music while you are doing other things --
Personal stereo sets are not capable of generating very high volumes, although the use of earphones means that lower volumes are more concentrated.
However, quarter-inch phone connectors are still common in professional audio, and miniature phone connectors (3.5 mm) are predominant in personal stereo systems.
I should also like to recommend that the habit of cycling while wearing and listening to personal stereo systems should become an offence.
I thought that he might have nodded off and that perhaps the headphones were his personal stereo.