The System Lacks Bass or High Frequencies

If the speakers lack bass this could be a result of out of phase wiring. This occurs when the positive and negative wires are connected incorrectly. The positive and negative wire connection at the source must be the same at the speaker connection. Most speakers will have a positive (+) sign and/or a negative (—) sign on the terminal, with some featuring a red mark for positive and / or a black mark for negative. If you have confirmed the wiring is correct and still lack bass you can also verify that the speakers are attached firmly to the mounting surface, and that the tone settings for each zone are accurate.