Rockbox connect to speaker, only background music, no singer

[yybluffside]

Hi, all,

I have just installed Rockbox on my Sansa e250, and noticed something odd.  The songs seem fine when I listen to them on my earphone. However, when I connect the MP3 to a speaker, only background music comes through. The singer's voice disappears. I have checked the sound setting, and it is NOT on Karaoke mode. Could someone help to understand what is going on？ Thank you!

[dreamlayers]

Often, in stereo music the singer's voice is equally on both channels, but the stereo position of other sounds varies. If you connect a speaker between the left and right channels, you won't hear the singer. Normally, you would use two speakers, one connected between left channel and ground and the other between right channel and ground. If you use two speakers meant to work like that, but the ground connection is broken, you in effect have two speakers in series between the left and right channel and you also won't hear the singer.