Since we don't know much about your HT system its hard to say why the difference in volume. ravi is correct in that some source materials are different in the "loudness" of the center channel. But other things can cause the differences as well. Be sure you center channel speaker "setting" on your receiver is correct (large or small). Since the speakes have different sensitivities and dispersion patterns, this can add to the imbalance problem. Another is room acoustics. If you receiver allows a "rotating" pink noise signal to be sent to each speaker (i.e. LF C RF RR LR) and again and again, then sit in your best listening spot and adjust the center and rear channels to match the front speakers for proper balance (loudness) Its OK if the settings for the center are higher than the fronts, ( and for the surrounds, etc) All things considered, it would be incredible if all speakers were actually set to the same setting for proper balance!