Double check volume and position control on the adjustments first.
With only 2 wires you either wired them correctly (in phase) or incorrectly (out of phase) which will effect the response in the lower frequency sound as well the total volume. You can look at the factory speaker and test for the correct polarity with a battery and then see which terminal is positive and relate that to your new installation of the replacement speakers. Look on the internet for the procedure on how to test for speaker polarity.