I just got my 15" icon dual 2 on monday =) So anyway im probably about 75% done building a fiberglass box for it and I may have to invert the sub to get the neccesary air space. When i do that I have to reverse the polarity correct? So for a 1 ohm load at the amp I would run amp + to sub - on voice coil 1 and amp - to sub + on voice coil 2 and then connect the remaining 2 terminals together. Is that correct?

If it's just a single sub, you don't have to reverse polarity.

It may sound better that way, or it may not, but it's the same as if you had it mounted the other way.

Now, if you had one inverted and the other not, things would be different...

Okay, thankyou... I have never inverted a sub or had a sealed setup lol.

also, your example describes series wiring. That will net you a 4 ohm load. This is not the same as reversing polarity. All that you would do to reverse polarity is switch the wires going to the AMP. That is to say, switch the + lead to the -, and vice versa. You would not switch any wires on the dual voice coil sub. To get a 1 ohm load you'll still want to wire the sub in parallel- all positives together to the + on the amp and all negatives together to the - on the amp.

Whether you'll have to reverse polarity depends on how it sounds once installed. If it's out of phase with the interior speakers you'll want to switch the polarity. However, this is not always a given when you invert the sub, as Jim mentioned. It's just like interior speakers- sometimes switching polarity in one will yield better results. It's not necessary to have every speaker in your vehicle in phase.

Is there every a time when it is a complete 'no-no' to reverse polarity? Or is it just a different sound? (Obviously, I have never done this.)

There is never a time when it will hurt anything to wire two separate speakers in different polarities. It is simply about how it sounds. In my old car I found out that the best sound came when the right front and left rear speakers were out of phase with the other two. Similarly, right now I believe I have the right tweeter out of phase with the mid on that side and both speakers on the left side in my front stage.

There are times when you HAVE to wire speakers out of phase, such as in an isobaric subwoofer setup. But that's really the only time I can think of.

ok thankyou for the advice. one more quick question though, my amp also has phase on it as well. So if I do reverse the wiring do I also turn the phase to 180 as well? Its a sundown sae 1000.

Reversing the wiring is 180 out of phase... so do one or the other. If you do both, you are just back where you started.