You can check phase REALLY easily with a 9v battery.
Find a smoke detector and rob it of it's battery for a minute.

Seriously, I keep fresh ones around just for this purpose.
With all four subs wired up, go to your amplifier, your final wiring there, and disconnect the wires from the amp.
Touch the end of the wires to the battery... positive wire to the positive terminal on the battery.
You SHOULD see all the cones move OUT simultaniously, and stay out until you remove the battery.
If one of them moves IN instead, you have found your culprit.
And if they all move out together - you've confirmed that they are all wired relatively "in phase".
This is the easiest, fastest way to check phase, and it's correct every time - even in cases where the speaker terminals may have been installed backwards or marked incorrectly.

You can check phase REALLY easily with a 9v battery.
Find a smoke detector and rob it of it's battery for a minute. :p
Seriously, I keep fresh ones around just for this purpose.
With all four subs wired up, go to your amplifier, your final wiring there, and disconnect the wires from the amp.
Touch the end of the wires to the battery... positive wire to the positive terminal on the battery.
You SHOULD see all the cones move OUT simultaniously, and stay out until you remove the battery.
If one of them moves IN instead, you have found your culprit.
And if they all move out together - you've confirmed that they are all wired relatively "in phase".
This is the easiest, fastest way to check phase, and it's correct every time - even in cases where the speaker terminals may have been installed backwards or marked incorrectly. ;)