My center speaker and cable are working and no loose wires. As I mentioned, Yamaha A/V receivers has a function of "5 channels", were in all speakers are ON (5.1). All are active, acting voice and background, not separated, when that is enabled center is working fine. So its not my loose wire or defective speaker. I just want to find out if someone experienced this, if it is the receiver or the optical cable, that's malfunctioning?