If the speaker wire connections on one side are swapped, this can result in a sound that is "scooped" where the lower frequency sounds that are mostly equal between the left and right speakers are reaching you out of phase with one another. This can result in the speakers sounding like they are lacking in bass. To check for this, make sure that the speaker wires are connected to the same color 5-way binding post on each side.
Why don't my speakers have more bass?
