two dvc 4 ohm subs on a 2 ch amp

with the coils wired series to 8 ohms, then the subs wired parallel to 4 ohms i will have a  4 ohm load......when i hook this 4 ohm load up to a 2 channel  amp using the left positive output and the right negative output the amp will see a 4 ohm load or a 2 ohm load ?  I see it as a 4 ohm load but I have been told by others that since I am using the left positive and right negative the ohm load will be cut in half again ??  is this true ?  i dont see how the impedance can change without wiring the subs differently. can someone help me clear this up ??????