The impedance makes very little difference and it only affects volume not quality of sound. The problem is likely the fact that they are the wrong types of speakers for the system (assuming a Monsoon system) and could also be wired incorrectly. For example, any coaxial speaker will sound bad in the sail panels because the amp is designed for subs there and only provides low frequency signal.
White 2000 Trans Am (sold)
White 2011 Mustang Convertible
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